Hydraulic system, work device and method

Abstract

A hydraulic system, a work device and a method for generating a quick movement and a load movement with hydraulic cylinders. A hydraulic system (1) comprises a quick movement cylinder (2) and an additional cylinder (3), wherein piston rods (4, 5) of the hydraulic cylinders are connected mechanically (6) to each other. By means of a control valve (12), a hydraulic oil flow is directed to act selectively only on either the quick movement cylinder for generating the quick movement or, in addition to the quick movement cylinder, also on the additional cylinder for generating the load movement in a working movement direction. During the quick movement and return movements, hydraulic oil is circulated between working pressure spaces (13, 1144)) of the additional cylinder by means of a circulation system (15) also having a pressure accumulator (18) for storing the hydraulic oil.

Description

[0001] Hydraulic system, work device and method

[0002] Background of the invention

[0003] The invention relates to a hydraulic system having two or more hydraulic cylinders connected to perform quick movements and movements requiring high force .

[0004] Further, the invention relates to a work device and to a method utili zing said hydraulic system .

[0005] The subj ect matter of the invention is described in more detail in the preambles of the independent claims o f the application .

[0006] Hydraulic cylinders are used in a wide variety o f ways in di f ferent types of machines and systems to generate movement by means of pressuri zed hydraulic oil . Hydraulic cylinders are reliable , simple , inexpensive and may generate high forces . When quick movement and, on the other hand, high force are required, the use of special cylinders is known . Further, various multi-cylinder control systems have been developed for generating quick movements and high- force movements . However, some shortcomings have been identi fied in the current solutions .

[0007] Brief description of the invention

[0008] The idea of the invention is to provide a novel and improved hydraulic system, work device and method .

[0009] The characteristic features of the hydraulic system according to the invention are defined in the characteri zing part of the first independent device claim .

[0010] The characteristic features o f the work device according to the invention are defined in the characteri z ing part of the second independent device claim .

[0011] The characteristic features of the method according to the invention are defined in the characteri zing part of the independent method claim .

[0012] The idea of the proposed solution is that the hydraulic system comprises multiple hydraul ic cylinders , the operation of which may be controlled to generate a quick movement and a higher-force load movement . The hydraulic system comprises a quick movement cylinder and one or more additional cylinders . The quick movement cylinder is used to perform a simultaneous quick movement of all hydraulic cylinders in a working movement direction and a return movement in a return direction . The hydraulic system has a control valve which is normally in a quick movement position and prevents a hydraulic oil flow to the additional cyl inder . When the control valve changes its control position from the quick movement position to a load position, hydraulic oil can also flow to the additional cylinder, in which case the additional cylinder and the quick movement cylinder together perform the load movement in the working movement direction . The hydraulic system further comprises a circulation system in which the hydraulic oil can flow between working pressure spaces of the additional cylinder when the control valve is in the quick movement position . As there are unequal working pressure space volumes in the additional cylinder in the working pressure spaces located on di f ferent piston sides , the circulation system is equipped with one or more pressure accumulators that may receive and discharge hydraulic oil . The pressure accumulator may thus compensate for the oil volumes due to unequal working pressure spaces .

[0013] One advantage of the proposed solution is that the hydraulic system for generating a quick movement and a higher- force movement , i . e . a load movement , is simple and assemblable from basic hydraulic components available on the market as such . Thus , the hydraulic system is inexpensive to manufacture and its maintenance and replacement of the components are easy to carry out .

[0014] Further, an advantage of the solution is that the system is energy-ef ficient , as hydraulic oil of the additional cylinder is circulated in the circulation system during the quick movement and the return movement without being conveyed out of the system through outlet channels . Hence , warming-up of the hydraul ic oi l due to constriction losses may be avoided . Further, pressure energy is recovered by means of the pressure accumulator of the circulation system .

[0015] It may further be stated that the proposed solution may be referred to as an acceleration system, the purpose of which is to accelerate the working cycle of the hydraulic cylinders when force requirement is low . In a low- force situation the hydraulic flow being fed drives only the first hydraulic cylinder, whereby the available hydraulic flow provides quick working and return movements when no hydraulic flow is directed in this situation to the second hydraulic cylinder . When the resistance to movement increases and higher force is required to move the hydraulic cylinders in the working movement direction, a connection to the working pressure space of the additional cylinder is opened, whereby the additional cyl inder performs the working movement together with the quick movement cylinder .

[0016] More speci fical ly, a hydraulic system for generating a quick movement and a load movement comprises : a quick movement cylinder and at least one additional cylinder, wherein piston rods of said hydraulic cylinders are connected mechanical ly to each other, whereby the piston rods are arranged to move simultaneously outwards in a working movement direction and inwards in a return direction; a first pressure line and a second pressure line for feeding a hydraulic oil flow into the hydraulic system and out of the hydraulic system; and at least one control valve for directing an oil flow selectively to at least one of said hydraulic cylinders to select a simultaneous quick movement and load movement of all hydraulic cylinders in the working movement direction . Further, said control valve of the hydraulic system comprises a quick movement position in which the control valve is arranged to prevent the hydraulic oil flow fed into the hydraul ic system from flowing to said at least one additional cylinder, whereby the hydraulic oil flow fed into the hydraulic system is arranged to act only on a piston-side working pressure space of the quick movement cylinder for generating the quick movement . Additionally, the control valve has a load position in which the control valve is arranged to direct the hydraulic oil flow fed into the hydraul ic system to also act on a piston-side working pressure space of said at least one additional cylinder for generating the load movement by means of the quick movement cylinder and said at least one additional cylinder . The hydraulic system also comprises a circulation system for conveying hydraulic oil between the piston-side working pressure space and a rod-side working pressure space of said at least one additional cylinder in response to said quick movement in the working movement direction and a return movement in the return direction; and which circulation system comprises at least one pressure accumulator that is arranged to compensate for di f ferences in volumes of the piston-side and the rod-side working pressure spaces of said at least one additional cylinder by receiving and discharging hydraulic oil .

[0017] According to one embodiment , working pres sure spaces of the quick movement cylinder are in continuous communication with the first pressure line and with the second pressure line of the hydraulic system independently of said control valve , whereby the quick movement cylinder is arranged to perform movements according to its work cycle in the working movement direction and in the return direction during the quick movement and the load movement .

[0018] According to one embodiment , the quick movement cylinder and said at least one additional cylinder are hydraulic cylinders that are separate from each other and are arranged side by side with respect to each other . In other words , multiple separate hydraulic cylinders connected physically side by side are arranged to carry out a simultaneous quick movement and high- force load movement . An advantage of this solution is that the separate hydraulic cylinders may be easily selected and si zed for each speci fic case . In addition, the separate hydraulic cylinders may be easily removed for maintenance and a damaged hydraulic cylinder may be replaced with a new one i f necessary . The use of multiple separate hydraulic cylinders thus improves the serviceability of the system and increases the flexibility of the solution .

[0019] According to one embodiment , all hydraulic cylinders connected to the hydraulic system, i . e . the quick movement cylinder and one or more additional cylinders , are double-acting standard cylinders . In other words , ready basic cylinders available on the market are utilized in the embodiment . The solution does therefore not require special cylinders to be designed and manufactured, whereby the practical implementation of the solution is easy, the price is low, and in addition, the availability of components and their replaceability are good .

[0020] According to one embodiment , all hydraulic cylinders connected to the hydraulic system, i . e . the quick movement cylinder and one or more additional cylinders , are hydraulic cylinders that are identical to each other . In this case , the solution is particularly simple . When these identical cylinders are controlled as described in this document , a high-speed quick movement , and on the other hand, a high- force load movement are provided by a simple hydraulic connection .

[0021] According to one embodiment , the hydraulic system comprises two or more hydraulic cylinders that are di fferent from each other . In this case , it is for example possible that the quick movement cylinder is di f ferent from the additional cylinder . Further, in case there are two additional cylinders or even more of them, these additional cylinders may be identical to or di fferent from each other . The quick movement cylinder may be selected to provide a high-speed movement with lower force , while the additional cylinders may be selected to provide high force with a slower movement .

[0022] According to one embodiment , said at least one control valve is a pressure-controlled valve which has a preset pressure limit and is arranged to change its control position from the quick movement pos ition to the load position in response to pressure in the piston-side working pressure space of the quick movement cylinder exceeding said pressure limit . In other words , the control valve is normally in the quick movement position and changes its control position to the load position when force resisting the quick movement increases and pressure of the hydraulic oil rises as a result in the piston-side working pressure space of the quick movement cylinder .

[0023] According to one embodiment , a feed channel leads to the control valve , which feed channel is in communication with a channel leading to the piston-side working pressure space of the quick movement cylinder . The control valve is additionally in communication with the feed channel by means of a detection channel . The control valve changes its position to the load position on the basis of pressure in the detection channel .

[0024] According to one embodiment , said at least one control valve is an electrically controlled valve which i s arranged to change its control position between the quick movement position and the load position under control of a control signal received from a control unit . In other words , the control unit may control the operation of the control valve for example on the basis of a program or an algorithm set in the control unit . Further, the control unit may be arranged to receive commands from a user interface or from control means to select the quick movement and the load movement . Further , it is possible that the control unit i s arranged to receive pressure data from one or more pressure sensors connected to the hydraulic system to detect a force resisting the quick movement . As the pressure exceeds a predetermined limit value , the control unit gives a control signal to the electrically operated control valve .

[0025] Further, it is possible to arrange sensors measuring load and resistive forces , such as strain-gauges , in connection with the mechanical structure , the data received from which sensors may be used to control the control valve between the quick movement position and the load position .

[0026] According to one embodiment , the circulation system comprises at least one pressure relief valve which is arranged to allow hydraulic oil to flow out from the circulation system in response to a preset pressure of the pressure rel ief valve being exceeded . In other words , when the pressure accumulator is full and can no longer receive any more hydraulic oil , the pressure of the hydraulic oil in the circulation system rises , and when the pressure exceeds the preset pressure of the pressure relief valve , hydraulic oil is allowed to flow out from the circulation system .

[0027] When the additional cylinder performs a return movement after the load movement , the piston pushes hydraulic oil that has been fed through the control valve for the load movement to the piston-side working pressure space into the circulation system . Thus , an additional amount of hydraulic oil is introduced into the circulation system under the ef fect of the return movement following the load movement of the additional cylinder . When the pressure accumulator cannot receive this additional amount of hydraulic oil and the pressure in the circulation system rises , the pressure relief valve allows hydraulic oil to flow out from the circulation system .

[0028] According to one embodiment , the pressure accumulator connected to the circulation system is a pre-pressuri zed pressure accumulator in which the separating element between a gas space and a fluid space is a bladder, a membrane or a piston .

[0029] According to one embodiment , the pressure accumulator connected to the circulation system i s a spring-loaded pressure accumulator in which the separating element is a spring-loaded piston .

[0030] According to one embodiment , the pressure accumulator connected to the circulation system is any type o f pressure accumulator or container that is able to receive hydraulic oil and is able to return it back to the hydraulic system .

[0031] According to one embodiment , the hydraulic system comprises , side by side , a first additional cylinder and a second additional cylinder which are connected to the same circulation system . In this case , the piston-side working pressure spaces of the additional cylinders are connected to each other, and correspondingly, the rod-side working pressure spaces of the additional cylinders are connected to each other .

[0032] According to one embodiment , the hydraulic system comprises , side by side , a first additional cylinder and a second additional cylinder . The f irst additional cylinder is connected to a first circulation system which has a first pressure accumulator, and the second additional cylinder is connected to a second circulation system which has a second pressure accumulator . In other words , the hydraulic system comprises multiple additional cylinders , each of which have their own circulation system . The circulation systems are as described in this document .

[0033] According to one embodiment , the hydraulic system comprises multiple additional cylinders side by side , whereby these additional cylinders may be arranged to be connected to generate force in the working movement direction in stages depending on the magnitude of the force resisting the movement . Detection o f the force and connection of the additional cylinders to perform the load movement may be implemented using unequal preset pressures in separate control valves , or alternatively, pressure sensors or force sensors may be used to detect the magnitude of the resistive force , and electric control valves may be controlled by means of a control unit .

[0034] According to one embodiment , the proposed solution also relates to a work device which comprises : a body which is equipped with a connecting device for attaching the work device to a movable working machine ; at least one working element which is arranged movably relative to the body; and a hydraulic system for moving said working element . Further, the hydraulic system for moving said working element is in accordance with any of the embodiments and features described in this document .

[0035] In other words , the work device is arranged to be operated by means of hydraulics of the movable working machine . On the chassis of the working machine there is a hydraulic pump for providing the necessary oil flow . In addition, a tank of the hydraulic system is on the chassis .

[0036] Use of the hydraul ic system described in this document in a movable working machine for operating the work device is advantageous because by means o f the circulation system of the additional cylinder, hydraulic oil needs to be removed from the hydraulic system for the most part only during the return movement of the quick movement cylinder . From the additional cylinder, hydraulic oil is removed in minor amounts only during the return movement following the load movement , in case the pressure accumulator i s already full . When hydraulic oil does not need to be trans ferred during the use of the work device in large amounts between the hydraulic pump and the tank located on the chassis and the additional cylinders o f the work device , constrictions of the hydraulic oil flow in long hydraulic channels and hoses as well as warming up of the hydraulic oil due to the constrictions are avoided . In addition, when hydraulic oil may be circulated in the circulation system and stored in the pressure accumulator, energy may be saved . According to one embodiment , the work device is arranged or is arrangeable to a boom of the movable working machine .

[0037] According to one embodiment , the work device is a device intended for handling timber .

[0038] According to one embodiment , the work device is a device intended for pulveri zing concrete and corresponding materials , or it may alternatively be a gripper intended for collecting and handling heavy obj ects .

[0039] According to one embodiment , the work device is a timber grab which has a first aw part and a second j aw part , both connected to the body so as to rotate by means of rotation pins thereof , whereby the j aw parts are rotatable towards each other and away from each other . In the hydraulic system a quick movement cylinder and an additional cylinder disposed side by side are arranged to rotate the first j aw part relative to the body . Further, a rotation movement of the first j aw part is transmitted by means of a connection element, such as a strut bar, to the second j aw part to provide a simultaneous rotation movement thereof .

[0040] According to one embodiment , both j aw parts comprise two curved j aws , and additionally, the j aws of the j aw parts are located relative to each other in such a way that they move in an interlaced manner .

[0041] According to one embodiment , the timber grab is equipped with at least one blade which is attached to the body and against which the first and the second j aw part are arranged to press wood being handled for cutting it . In other words , the timber grab i s a device intended for cutting and handling timber, applying the guillotine principle for cutting the timber . The timber grab may thus be a device intended for collecting energy wood and smallwood .

[0042] The first j aw part is moved by means of the quick movement cylinder during handling of the timber, whereby the j aw parts of the timber grab move fast . When force resisting the movement of the j aw parts in the working movement direction, i . e . in the pressing direction, increases , for example when cutting the timber against the blade element , the additional cylinder can be used to increase the pressing force i f necessary . The hydraulic system may automatically detect the increased force requirement and connect the additional cylinder to work .

[0043] According to one embodiment , the blade is a blade plate attached immovably to the body .

[0044] According to one embodiment , the blade is a blade plate attached movably to the body . The blade plate may be moved by means of the hydraulic system described in this document , whereby the blade plate has a quick movement and a load movement . In this case , rotation of the aws and movement of the guillotine blade of the timber grab may both utili ze the hydraulic system described in this document , or alternatively it is utili zed to move only the j aws or the blade plate .

[0045] According to one embodiment , the solution also relates to a method for generating a quick movement and a load movement with hydraulic cylinders , and in which method : a hydraulic system is used, the hydraulic system having a quick movement cylinder and at least one additional cylinder, wherein piston rods of said hydraulic cylinders are connected mechanically to each other, whereby the piston rods are arranged to move s imultaneously outwards in a working movement direction and inwards in a return direction; and operation of the quick movement cylinder and of the additional cylinder is controlled by means of a control valve to generate the quick movement and the load movement in the working movement direction . Further, in the method : the quick movement is performed by conveying a hydraulic oil flow into a piston-side working pressure space of the quick movement cylinder and the hydraulic oil flow into a piston-side working pressure space of the additional cylinder is prevented in a quick movement position of the control valve ; the load movement is performed by changing a control position of the control valve to a load position and by directing the hydraulic oil flow through the control valve to also act on the piston-side working pressure space of the additional cylinder, whereby the quick movement cylinder and the additional cylinder together perform the load movement in the working movement direction; hydraulic oi l is circulated between the piston-side working pressure space and the rod-side working pressure space of the additional cylinder in a circulation system during the quick movement and return movement ; and di f ferences in volumes of the piston-side and the rod-side working pressure spaces of the additional cylinder are compensated for by receiving hydraulic oil with a pressure accumulator connected to the circulation system and by discharging hydraulic oil from the pressure accumulator .

[0046] According to one embodiment , the method comprises additionally removing hydraulic oil from the circulation system only when the pressure accumulator is full and the pressure of the hydraulic oil in the circulation system exceeds a set pressure limit .

[0047] The above embodiments and the features defined therein may be combined to achieve desired solutions .

[0048] Brief description of the figures

[0049] Some embodiments of the proposed solution are illustrated in more detail in the following figures , in which Fig . 1 schematical ly represents one hydraulic system having two hydraulic cylinders side by side and a pressure-controlled control valve ,

[0050] Fig . 2 schematically represents another hydraulic system having an electrically controlled control valve ,

[0051] Fig . 3 and 4 schematically represent some hydraulic systems having, in addition to a quick movement cylinder, two additional cylinders connected in alternative ways , and Fig . 5 and 6 represent , schematically and from different angles , one hydraulically operated work device .

[0052] For clarity, some embodiments of the proposed solutions are illustrated in the figures in a simpli f ied form . The same reference numbers have been used in the figures to refer to the same elements and features .

[0053] Detailed description of some embodiments

[0054] Fig . 1 illustrates a hydraulic diagram of one hydraulic system 1 , showing that the hydraulic system 1 comprises two hydraulic cylinders arranged side by side , a quick movement cylinder 2 and an additional cylinder 3 . Piston rods 4 , 5 o f the hydraul ic cylinders 2 , 3 are connected mechanically 6 to each other, whereby they move in a working movement direction ( + ) and in a return movement direction ( - ) simultaneously regardless of which cylinder 2 , 3 receives the hydraulic flow into the working pressure spaces thereof from hydraulic pressure channels P- and P+ . The hydraulic pressure flows in channels P- and P+ may be controlled by a check valve 7 . The check valve 7 may be for example a 4 / 2 check valve and it is arranged to connect the pressure lines P- and P+ to a tank 8 and to a hydraulic pump 9 .

[0055] The mechanical connection between the piston rods 4 , 5 may be provided by a movable construction to which the piston rods 4 , 5 are attached, or alternatively, a separate connecting element may be arranged between the piston rods 4 , 5 . The hydraulic cylinders 2 , 3 may be conventional commercially available hydraulic cylinders . The operation of the hydraulic system 1 does not require the use of special cylinders , and does not set special requirements for the properties of the hydraulic cylinders .

[0056] Fig . 1 illustrates a high-speed quick movement situation in which high force is not required but it is essential to provide high-speed movements in the working movement direction ( + ) and in the return direction ( - ) . The hydraulic oil is conveyed only into a pistonside working pressure space 10 o f the quick movement cylinder 2 . When the full volume flow from line P+ is conveyed only into working pressure space 10 , a high speed of movement is achieved . A rod-side working pressure space 11 i s connected to the tank 8 through channel P- . A control valve 12 prevents the access of hydraulic oil from channel P+ into a piston-side working pressure space 13 of the additional cylinder 3 , in which case the additional cylinder 3 does not participate ( + ) in generating the movement . As the quick movement cylinder 2 at the same time moves the additional cylinder 3 , it causes hydraulic oil flow in working pres sure spaces 13 and 14 of the additional cylinder 3 . The hydraulic system 1 comprises a circulation system 15 , whereby the hydraulic oil of the additional cylinder 3 is pushed by a piston 16 and is able to circulate through the control valve 12 from a rod-side working pressure space 14 of the additional cylinder 3 through a channel 17 into the piston-side working pressure space 13 .

[0057] The control valve 12 is pressure-controlled and spring force may hold it in the quick movement position according to the figure . When the piston 16 of the additional cylinder 3 moves left in the figure , it thereby pushes hydraulic oil from working pressure space 14 into channel 17 and further through the control valve 12 into working pressure space 13 . The volume change caused by the movement is greater in working pressure space 13 than in working pressure space 14 , because in the rod-side working pressure space 14 the piston rod 5 takes up part of the volume . Therefore , a necessary additional amount of hydraulic oi l flows from a pressure accumulator 18 into the piston-side working pressure space 13 to compensate for this di f ference in volume .

[0058] The return movement ( - ) is achieved by conveying hydraulic oil flow P- from the channel into working pres sure space 11 of the quick movement cylinder 2 and by connecting working pressure space 10 to the tank 8 by means of the check valve 7 . When the whole hydraulic oil flow from channel P- is conveyed only to the quick movement cylinder 2 , the return movement may be fast . Further, hydraulic oil is removed into the tank 8 through channel P+ only from working pressure space 10 of the quick movement cylinder 2 , whereby the amount of flow in channel P+ is relatively low and signi ficant constriction losses and generation of heat may be avoided .

[0059] The return movement ( - ) o f the quick movement cylinder 2 also moves the additional cylinder 2 in the return direction, whereby the hydraulic oil flows from working pressure space 13 through the control valve 12 and further through channel 17 into working pressure space 14 . As working pressure space 14 holds less hydraulic oil than what is removed from the piston-s ide working pressure space 13 due to the volume taken up by the piston rod 5 , part of the hydraulic oil flows into the pressure accumulator 18 in which it is stored for reverse ( + ) movement . I f the pressure accumulator 18 is full and the pressure thereinside increases over a preset value of a pres sure relief valve 19 , the pressure relief valve 19 allows hydraulic oil to flow through channel 20 into channel P+ and further into the tank 8 .

[0060] As resistance in the working movement direction ( + ) increases , the pressure rises in channel P+ leading to working pressure space 10 of the quick movement cylinder 2 and in a feed line 21 to the additional cylinder 3 connected to it . In the control position o f the control valve 12 as shown in Fig . 1 , the hydraulic oil is not able to flow through the control valve 12 into working pressure space 13 . When the pressure increases in a detection line 22 of the control valve 12 , the control valve 12 changes its control position upward in Fig . 1 and al lows the hydraulic oil flow to pas s through into working pressure space 13 . As a result , the additional cylinder 3 is connected to perform the load movement in the working movement direction ( + ) together with the quick movement cylinder 2 , whereby higher force is provided . When the strong movement stops , pressure line P+ is connected to the tank 8 , whereby also the pressure in the feed line 21 and in the detection line 22 drops with the result that the control valve 12 again changes its position to the control position shown in Fig . 1 and allows the hydraulic oil flow to circulate in the circulation system 15 from working pressure space 13 through channel 17 into working pressure space 14 .

[0061] The control valve 12 may be a directly pressure- controlled spring-loaded 3 / 2 valve . The pressure accumulator 18 may be a gas accumulator comprising a hydraulic oil space , a separator element and a gas space which is prepressuri zed .

[0062] The hydraulic system 1 shown in Fig . 2 di ffers from the hydraulic system of Fig . 1 in that the control valve 12 is electrically controlled and i s connected by means of a control line 23 to be control led by a control unit CU . The hydraulic system 1 may comprise one or more sensors S , such as pressure sensors , the detection data of which may be transmitted to the control unit CU for controlling the control valve 12 . Further, the control unit CU may be in communication with a user interface UI or other control means by which control commands , parameters and algorithms may be provided to the control unit for controll ing the operation of the control valve 12 . In the simplest form, the user may give control commands to the control unit CU for performing the quick movement and the load movement .

[0063] The hydraulic system 1 shown in Fig . 3 di ffers from the hydraulic system of Fig . 1 in that in addition to the quick movement cylinder 2 , it has two additional cylinders 3a and 3b . A piston-side working pressure space 13a o f additional cylinder 3a is connected to a piston-side working pressure space 13b of additional cylinder 3b, and correspondingly, rod-side working pressure spaces 14a, 14b are connected to each other . Further, the working pres sure spaces 13a - 14b are connected to the circulation system 15 corresponding to that shown in Fig . 1 . When the control valve 12 changes its control position from the quick movement position to the load position, both of the additional cylinders 3a, 3b participate in generating higher force . Instead of a pressure-controlled valve , the control valve 12 may be an electrically controlled valve as shown in Fig . 2 and may be controlled with a control signal obtained from the control unit or from another control means .

[0064] The hydraulic system 1 shown in Fig . 4 comprises two additional cylinders 3a, 3b, both having their own circulation system 15a, 15b as shown in Fig . 1 . The circulation systems 15a, 15b correspond to the circulation system shown in Fig . 1 and comprise similar hydraulic components . A preset pressure Px of a first control valve 15a may be equal or unequal to a preset pressure Py of a second control valve 15b . By the setting of the preset pressures Px, Py it i s possible to control whether the additional cylinders 3a, 3b participate in generating the load movement simultaneously, or whether only one additional cylinder participates first and the other additional cylinder participates only i f the force resisting the load movement still increases .

[0065] Fig . 5 and 6 show one work device 25 which may be operated utili zing some hydraulic system as described in this document . In the case of Fig . 5 and 6 the work device 25 is a timber grab 26 comprising a body 27 equipped with a connecting device for attaching the work device 25 to a movable working machine . The work device 25 also comprises working elements 28 which are arranged movably relative to the body 27 by means of the hydraulic system 1 . The hydraulic system 1 comprises a quick movement cylinder 2 and an additional cylinder 3 which may be control led as described in this document . In the timber grab 26 the working elements 28 comprise a first j w part 29 and a second aw part 30 , both connected to the body 27 so as to rotate by means of rotation pins 31 , 32 thereof , whereby the j aw parts 29 , 30 are rotatable towards each other and away from each other . The quick movement cylinder 2 and the additional cylinder 3 disposed side by side in the hydraulic system 1 are arranged to rotate the first j aw part 29 the body 27 and wherein the rotation movement of the first j aw part 29 is transmitted by means of connection elements 33 to the second j aw part 30 to provide a simultaneous rotation movement thereof . Both of the j aw parts 29 , 30 comprise two curved j aws 34 which are located relative to each other in such a way that they move in an interlaced manner .

[0066] The timber grab 26 may be equipped with a blade 35 which is attached to the body 27 and against which the first and the second j aw part 29 , 30 may press wood being handled for cutting it .

[0067] The figures and their description are intended solely to illustrate the idea of the invention . The scope of protection o f the invention, however, is defined in the claims of the application .

Claims

Claims1. A hydraulic system (1) for generating a quick movement and a load movement, which hydraulic system (1) comprises: a quick movement cylinder (2) and at least one additional cylinder (3, 3a, 3b) , wherein piston rods (4, 5) of said hydraulic cylinders are connected mechanically (6) to each other, whereby the piston rods (4, 5) are arranged to move simultaneously outwards in a working movement direction (+) and inwards in a return direction (-) ; a first pressure line (P+) and a second pressure line (P-) for feeding a hydraulic oil flow into the hydraulic system (1) and out of the hydraulic system (1) ; at least one control valve (12) for directing an oil flow selectively to at least one of said hydraulic cylinders to select a simultaneous quick movement and load movement of all hydraulic cylinders in the working movement direction; char ac t e r i z e d in that said control valve (12) comprises a quick movement position in which the control valve (12) is arranged to prevent the hydraulic oil flow fed into the hydraulic system (1) from flowing to said at least one additional cylinder (3) , whereby the hydraulic oil flow fed into the hydraulic system (1) is arranged to act only on a piston-side working pressure space (10) of the quick movement cylinder (2) for generating the quick movement; and which control valve (12) has a load position in which the control valve (12) is arranged to direct the hydraulic oil flow fed into the hydraulic system (1) to also act on a piston-side working pressure space (13) of said at least one additional cylinder (3) for generating the load movement by means of the quick movement cylinder (2) and said at least one additional cylinder (3) ;and wherein the hydraulic system (1) comprises a circulation system (15) for conveying hydraulic oil between the piston-side working pressure space (13) and a rod-side working pressure space (14) of said at least one additional cylinder (3) in response to said quick movement in the working movement direction (+) and a return movement in the return direction (-) ; and which circulation system (15) comprises at least one pressure accumulator (18) that is arranged to compensate for differences in volumes of the piston-side and the rodside working pressure spaces (13, 14) of said at least one additional cylinder (3) by receiving and discharging hydraulic oil.

2. The hydraulic system according to claim 1, char ac t e r i z e d in that working pressure spaces (10, 11) of the quick movement cylinder (2) are in continuous communication with the first pressure line (P+) and with the second pressure line (P-) of the hydraulic system (1) independently of said control valve (12) , whereby the quick movement cylinder (2) is arranged to perform movements according to its work cycle in the working movement direction ( + ) and in the return direction (-) during the quick movement and the load movement .

3. The hydraulic system according to claim 1, c h a r a c t e r i z e d in that the quick movement cylinder (2) and said at least one additional cylinder (3) are hydraulic cylinders that are separate from each other and are arranged side by side with respect to each other.

4. The hydraulic system according to any one of the preceding claims 1 - 3, c h a r a c t e r i z e d in thatsaid at least one control valve (12) is a pressure- controlled valve which has a preset pressure limit and is arranged to change its control position from the quick movement position to the load position in response to pressure in the piston-side working-pressure space (10) of the quick movement cylinder (2) exceeding said pressure limit.

5. The hydraulic system according to any one of the preceding claims 1 - 3, c h a r a c t e r i z e d in that said at least one control valve (12) is an electrically controlled valve which is arranged to change its control position between the quick movement position and the load position under control of a control signal received from a control unit (CU) .

6. The hydraulic system according to any one of the preceding claims 1 - 5, c h a r a c t e r i z e d in that the circulation system (15) comprises at least one pressure relief valve (19) which is arranged to allow hydraulic oil to flow out from the circulation system (15) in response to a preset pressure of the pressure relief valve (19) being exceeded.

7. The hydraulic system according to any one of the preceding claims 1 - 6, c h a r a c t e r i z e d in that the hydraulic system (1) comprises, side by side, a first additional cylinder (3a) and a second additional cylinder (3b) which are connected to the same circulation system ( 15) .

8. The hydraulic system according to any one of the preceding claims 1 - 6, c h a r a c t e r i z e d in that the hydraulic system (1) comprises, side by side, a first additional cylinder (3a) and a second additional cylinder (3b) ;and wherein the first additional cylinder (3a) is connected to a first circulation system (15a) which has a first pressure accumulator (18a) ; and wherein the second additional cylinder (3b) is connected to a second circulation system (15b) which has a second pressure accumulator (18b) .

9. A work device (25) which comprises: a body (27) which is equipped with a connecting device for attaching the work device (25) to a movable working machine; at least one working element (28) which is arranged movably relative to the body (27) ; and a hydraulic system (1) for moving said working element (28) ; char ac t e r i z e d in that the hydraulic system (1) for moving said working element (28) is in accordance with any one of the preceding claims 1 - 8.

10. The work device according to claim 9, c h a r a c t e r i z e d in that the work device (25) is a timber grab (26) which has a first jaw part (29) and a second aw part (30) , both connected to the body (27) so as to rotate by means of rotation pins (31, 32) thereof, whereby the jaw parts (29, 30) are rotatable towards each other and away from each other, and in which hydraulic system (1) a quick movement cylinder (2) and an additional cylinder (3) disposed side by side are arranged to rotate the first jaw part (29) relative to the body (27) ; and wherein a rotation movement of the first jaw part (29) is arranged to be transmitted by means of at least one connection element (33) to the second jaw part (30) to provide a simultaneous rotation movement thereof.

11. The work device according to claim 10, c h a r a c t e r i z e d in that the timber grab (26) is equipped with at least one blade (35) which is attached to the body (27) and against which the first and the second jaw part (29, 30) are arranged to press wood being handled for cutting it.

12. A method for generating a quick movement and a load movement with hydraulic cylinders (2, 3) ; in which method: a hydraulic system (1) is used, the hydraulic system having a quick movement cylinder (2) and at least one additional cylinder (3) , wherein piston rods (4, 5) of said hydraulic cylinders (2, 3) are connected mechanically (6) to each other, whereby the piston rods (4, 5) are arranged to move simultaneously outwards in a working movement direction (+) and inwards in a return direction (-) ; operation of the quick movement cylinder (2) and of the additional cylinder (3) is controlled by means of a control valve (12) to generate the quick movement and the load movement in the working movement direction (+) , char ac t e r i z e d in that the quick movement is performed by conveying a hydraulic oil flow into a piston-side working-pressure space (10) of the quick movement cylinder (2) and the hydraulic oil flow into a piston-side working pressure space (13) of the additional cylinder (3) is prevented in a quick movement position of the control valve (12) ; the load movement is performed by changing a control position of the control valve (12) to a load position and by directing the hydraulic oil flow through the control valve (12) to also act on the piston-side working pressure space (13) of the additional cylinder (3) , whereby the quickmovement cylinder (2) and the additional cylinder (3) together perform the load movement in the working movement direction (+ ) ; hydraulic oil is circulated between the piston-side working pressure space (13) and a rod-side working pressure space (14) of the additional cylinder (3) in a circulation system (15) during the quick movement and return movement; and differences in volumes of the piston-side and the rod-side working pressure spaces (13, 14) of the additional cylinder (3) are compensated for by receiving hydraulic oil into a pressure accumulator (18) connected to the circulation system (15) and by discharging hydraulic oil from the pressure accumulator (18) .

13. The method according to claim 12, c h a r a c t e r i z e d in that hydraulic oil is removed from the circulation system (15) only when the pressure accumulator (18) is full and the pressure of the hydraulic oil in the circulation system (15) exceeds a set pressure limit.