HYDRAULIC ARRANGEMENT TECHNICAL FIELD The invention relates to a hydraulic device for the synchronization of two interacting hydraulic pistons, preferably two counter-impacting pistons for moulding at a high speed, comprising a first hydraulic piston and a second hydraulic piston, respectively; a first and a second hydraulic cylinder, respectively ; one to each hydraulic piston arranged pressing portion/impact portion ; a return surface and a working surface ; a return chamber and a working chamber provided in each cylinder ; a hydraulic conduit connected to each chamber; and at least a valve device for controlling the flow of oil to at least one of said conduits to synchronize the movements of the hydraulic pistons, characterized in that said valve device is connected between the conduit to the return chamber of the first hydraulic cylinder and to the working chamber of the second hydraulic cylinder, and that the conduit to the working chamber of the first hydraulic cylinder is connected to the conduit to the return chamber of the second cylinder.

PRIOR ART For certain hydraulic devices it is of vital importance that it is possible to synchronize the movements of the two interacting hydraulic pistons. With known technique, this is either too complex and hence also expensive and/or not reliable enough, especially if it is the question of hydraulic pistons that have to accelerate very rapidly and/or to supply heavy forces.

A specific field, where the above mentioned complex of problems is especially obvious, is impact machines for working of principally metal utilizing high kinetic energy.

Below, the complex of problems will be illustrated with reference to such an impact machine, but it should be understood that the invention is not limited to such machines.

Impact machines for working utilizing high kinetic energy are machines for working in the first place metal, such as cutting, punching, plastic forming of powder components, powder compaction, and similar operations, wherein the velocity of a ram, which may be a press piston, may be essentially higher than in conventional presses. Also polymeric and ceramic working materials may be conceivable, as well as different composites of metals, polymers and cerams. The working principle is based on the development of a very high kinetic energy of short duration instead of a high static press force of long duration. The dynamic forces of short duration, which are generated at the ram impact and which in impact machines of prior art are conveyed around in the

system via stands and foundations, may be several thousand times larger than with conventional presses and implies that considerable amounts of energy are lost in stands and foundations in stead of being utilized in an optimal manner for an effective work. In order to be able to absorb the large force pulses, impact machines of prior art are equipped with very strong and heavy stands and foundations according to the principles which are common in connection with conventional presses. Nevertheless, the dynamic, force pulses of shock type that are generated in impact machines are not damped in such heavy, conventional systems. The stress on all joints therefore become very large, as well as on sensitive components, e. g. electronic components for controlling those hydraulic valves which usually form part of impact machines, which causes a great risk of failure. Large, unwiedly stands also give rise to problems in connection with service, change of tool unit or of tool inserts in the tool unit, changing the height of the impact unit above the tool unit, etc. In the Swedish patent application No. 0002038-8, which has previously been filed by us, an invention is described, where an upper ram and a lower ram simultaneously are forced to make a single stroke at such a speed against an upper impact body being integrated into or pressing against an upper punch, and against a lower impact body, respectively, being integrated with or pressing against a lower punch, that those masses moving downwardly including the upper punch get a downwardly directed speed vl and those masses moving upwardly including the lower punch get an upwardly directed speed v2, wherein the movable parts have such masses and the speeds are so great that the pulses of the downwardly moving masses and the upwardly moving masses will be essentially of the same size. According to a specific embodiment of this method, it is desirable to be able to perform the movements for said rams completely synchronously, i. e. at exactly the same speed from a specific impact position. Today there is no suitable device on the market, which is capable to meet the last mentioned requirement, at least not in an economic and/or regularly suitable way.

DISCLOSURE OF THE INVENTION It is a purpose of the invention to minimize said complex of problems, which is achieved by a hydraulic device for the synchronization of two interacting hydraulic pistons, preferably two counter-impacting pistons for moulding at a high speed, comprising a first hydraulic piston and a second hydraulic piston, respectively; a first and a second hydraulic cylinder, respectively ; a to each hydraulic piston arranged pressing portion/impact portion; a return surface and a working surface; a return chamber and a working chamber provided in each cylinder ; a hydraulic conduit connected to each chamber; and at least one valve device for controlling the flow of oil to at least one of said conduits to synchronize the movements of the hydraulic pistons,

characterized in that said valve device is connected between the conduit to the return chamber of the first hydraulic cylinder and the working chamber of the second hydraulic cylinder, and that the conduit to the working chamber of the first hydraulic cylinder is connected to the conduit to the return chamber of the second cylinder.

Due to this solution a reliable and a cost efficient device for the synchronization of two hydraulic pistons can be achieved.

According to further aspects of the invention: -the size Al and A2, respectively, of the respective working surface is such that Al = 0,5 x A2, and the size A3 and A4, respectively, of respective return surface is such thatA3 =A4=Al ; -a refilling conduit connects to the connection between the working chamber of the first hydraulic cylinder and the return chamber of the second cylinder; -the pressure P2 in said refilling conduit is essentially lower than the pressure PI supplied to said valve device, and a non-return valve is provided in said refilling conduit; -a pressure sensing cut-off valve is provided in series with said non-return valve.

According to another aspect of the invention there is an object to provide a valve device, which in an optimal manner may be utilized to control the flow of oil in such a hydraulic device. It is important that said valve device quickly may provide great changes in the hydraulic flow to the device. According to preferred aspects of such an embodiment: -said valve device 1 comprises a valve housing l with a valve body 2 movably arranged within the valve housing, and at least a control mechanism 4 for controlling said movable valve body 2, wherein the valve body 2 is essentially sleeve-shaped and provided within the valve housing 1; -the valve body 2 is provided within the valve housing 1 in such a manner that it is essentially, preferably completely, counter-balanced in respect of hydraulic forces, acting in the radial direction ; -said valve body 2 is provided with a plurality of apertures 252,261,262 to enable the flow of hydraulic liquid in the radial direction through the valve body 2; -said valve body in the vicinity of said opening is provided with edge portions 272A, 272B on both the inner and the outer surfaces of the valve body, which edge portions 272A, 272B interact with the edge portions 103C, 104C and the channels 160,164 provided inside the valve housing 1 in such a manner that hydraulic liquid is allowed

to flow from each of said channels and beyond and between each of said edge portions, when the valve body 2 is positioned within the valve housing 1 to allow flow of oil to and from said hydraulic chamber 115, and that said edge portions at a different position of the valve body 2 interacts in a sealing manner, so that hydraulic liquid cannot flow to and from said hydraulic chamber 115; -the maximal, necessary movement of the valve body 2 within the valve housing 1 to move the valve body 2 from a completely closed position to a completely open position is between 0.1 and 3 % of the outer diameter D of the sleeve, preferably below 2 %, and more preferred below 1 % ; -the adjustment time for the valve body 2 from one end position to the other end position is below 10 msec, preferably below 5 msec ; -said device is part of an impact/pressing means intended to perform rapid impacts and/or to transmit heavy forces, wherein the valve body 2 has at least an inner diameter between 3 and 500 mm, preferably exceeding 50 mm, and more preferred exceeding 80 mm.

BRIEF DESCRIPTION OF DRAWINGS Below the invention will be described more in detail with reference to the accompanying drawings, of which Fig. 1 shows a principal connection diagram for a hydraulic device according to the invention; Fig. 2 shows a preferred embodiment of a valve device according to the invention ; Figs. 3 to 5 show different cross sections of a valve device according to Fig. 2; and Fig. 6 shows the principal construction of an impact machine, which advantageously is provided with a hydraulic device according to the invention.

DETAILED DESCRIPTION In Fig. 1 a principal connection diagram of a hydraulic device according to the invention is shown. A first hydraulic piston 400 and a second hydraulic piston 500, respectively, and a first 410 and a second 510 hydraulic cylinder, respectively, are shown. At respective hydraulic piston, a press portion/impact portion 501 and 401, respectively, a return surface 402 and 502, respectively, and a working surface 403 and 503, respectively, are shown. A return chamber 411 and 511, respectively, and a working chamber 412 and 512, respectively, are provided in each cylinder. A hydraulic conduit 420, 430,520,530 are connected to each chamber411, 412,511,512. A valve

device 1 is connected between the conduit 430 to the return chamber 411 of the first hydraulic cylinder, and to the working chamber 512 of the second hydraulic cylinder.

Further it is shown, that the conduit 420 to the working chamber 412 of the first hydraulic cylinder is connected to the conduit 530 to the return chamber 511 of the second cylinder. Pressurized oil PI is transmitted through the valve device 1 at a high pressure (e. g. about 300 bars) to one or the other of the connected conduits 430 and 520, respectively. Further it is shown that a refilling conduit 600 connects to the connection 420,530 between the working chamber 412 of the first hydraulic cylinder and to the return chamber 511 of the second cylinder. The pressure P2 in said refilling conduit 600 is essentially lower (e. g. 100 bars) than the pressure PI which is supplied to said valve device 1. A non-return valve 601 is provided in said refilling conduit 600 to prevent a return flow. Further, a pressure sensitive cut-off valve 603 is provided in series with said non-return valve 601, so that the refilling conduit only opens when a certain comparatively low pressure exists in the connection conduit 420,530. The size Al and A2, respectively, of respective working surface 403 and 503, respectively, is such that Al = 0,5 x A2. Further, the size A3 and A4, respectively, of said return surface 402 and 502, respectively, is such that A3 = A4 = Al.

The device of Fig. 1 functions such that when the upper conduit 430, as regarded from the valve, is pressurized, oil will be supplied to the return chamber 411 of the upper piston at 300 bars. Simultaneously, the working chamber 512 of the lower piston opens to the tank through a conduit 520. Then, a return stroke will begin, wherein oil is pressed out of the working chamber 412 of the upper piston and further through the connection conduit 430,520 to the return chamber 511 of the lower piston. Thereby a synchronous return movement is thus achieved. When the piston have moved the entire return stroke and have been positioned in an exactly correct starting position (preferably through stop lugs, not shown, provided within the cylinder or through position sensors), the working stroke may begin. This is achieved through the valve device 1 being reversed, so that the pressure PI is directed to the lower conduit 520 while the upper conduit is connected to the tank. The working chamber 512 will then be filled with highly pressurized oil, which will press against the larger working surface A2, so that the piston starts to move inwardly (upwardly in the figure). The oil in the upper chamber 511 is then pressed out and flows through the connection conduit 530 into the working chamber 412 of the second cylinder, whereby a synchronous working stroke may be performed. Principally, a direction valve of standard type be used as the valve device 1, but in order to be able to perform such a working stroke at a heavy force/high kinectic energy it is advantageous that very rapidly be able to create the necessarily

large flow paths, which implies certain requirements on the valve device 1, which are not met without problems by such devices according to prior art. Thus, in Figs. 2 to 5 a preferred valve device is shown, which should be used in a hydraulic device according to Fig. 1 (it is, however, realized that the invention is not limited to the use of such a valve).

In Fig. 2 a valve device 1 is shown, in a longitudinal cross section, according to a preferred embodiment of the invention. The device comprises a valve housing 100, a valve body 2 movably arranged within the valve housing, and a control mechanism 4.

The valve housing 100 consists of a plurality of assembled parts, comprising an upper cover 102, an inner valve seat portion 103, and an outer valve seat portion 104. At the lower end of both said portions 103,104 a lower cover 106 is provided. At the very back of the valve housing 1 a lower and an upper, respectively, cavity/chamber 115 and 116, respectively, is provided, being separated by a wall portion 34, which is parallel to a plane P 1 across the longitudinal direction of the valve housing 100. There is a conduit 430 and 520, respectively, in communication with each cavity/chamber 115 and 116, respectively, (see Fig. 1).

In the outer valve seat portion 104 there is provided at least one inlet 107 for hydraulic liquid. In direct connection to the inlet 107 an annular channel 151 is provided (see also Fig. 3, which is a cross section along the line A-A of Fig. 2). In connection to said annular channel 151 there is a slot shaped cylindrical space 129, between the outer valve seat portion 104 and the inner valve seat portion 103, intended for the valve body 2, which is sleeve-shaped.

In connection to the annular chamber 151 there is in the outer valve seat portion 104 provided an upper annular portion with inwardly directed sharp edges 104A, and a lower annular portion with inwardly directed sharp edges/corners 104B. In a corresponding manner, on the inside of the slot space 128 and opposite to said annular corner/edge portions, also annular edge portions are formed in the inner valve seat portion 103, through an upper annular edge portion 103A and a lower annular edge portion 103B.

Said annular comer/edge portions 103, A, 103B, 104A, 104B interact with corresponding edge portions 271A, 271B, 273A, 273B on the axially movable valve body 2. The valve housing 104,103 and the valve body 2, respectively, are provided with four such annular edge means, arranged in pairs, of which only two interacts at a time in an opening manner while the other two pairs interact in a closing manner.

Further, the valve body 2 is provided with radial apertures 252,261,262,263,264 to enable the desired flows and hence the desired adjustment (see Fig. 3). At each side of the row of central apertures 252 in the valve body 2, a number of radial apertures 261 and 262, respectively, are provided in the valve body 2 in a symmetric manner in relation to the centre plane P 1 (see also Fig. 4). Said apertures provide communication between an outer annular chamber 163 and 164, respectively, which is provided in the outer valve seat portion 104 and an inner annular chamber 161 and 160, respectively, provided in the valve seat portion 103. Said inner chambers 160 and 161, respectively, communicate directly with the apertures 124 and 153, respectively, leading to respective pressure chamber 115 and 116, respectively, to which the respective hydraulic conduit 430 and 520, respectively, is connected. Finally, a valve body is shown, which is provided with an additional set of radial apertures 263 and 264, respectively, which are symmetrically arranged in relation to said plane P 1, and which are provided in the lower annular chamber 162 and the upper annular chamber 165, respectively. Said lower and upper annular chambers, respectively, communicate directly with the lower 119A and the upper 119B, respectively, outlets leading to a tank (see also Fig. 3).

Channels and apertures are arranged in the same way in connection to the outlet to the tank 119 as in connection with the channels communicating with the pressurized opening 107, so that a mirror symmetry in principle exists around a plane P 1. Further, there is shown (see also Fig. 5) that there are arranged a plurality of inlets 107 for hydraulic liquid.

Below as well as above the valve body 2 there are arranged one (or several) electro magnets 42A and 42B, respectively, for the adjustment of the valve body 2. Due to the limited movement requirement of the valve body said adjustment/movement of the valve body 2 can advantageously be performed in a magnetic way. The valve body 201 is magnetic us such, and therefore the electro magnets 42A, 42B on each sides of the valve body 2 may be utilized to control the positioning of the valve body 2.

A valve device according to the preferred embodiment shown in Fig. 2 functions as follows. Pressure exists through the inlets 107 and thus pressurizes the annular chamber 151 being in communication with the central apertures 252 of the valve body 2. When the positioning according to Fig. 2 is reached, no flow of hydraulic oil in any direction takes place, as all flow paths out of the annular chamber 151 and 260, respectively, are sealed, when the edges are overlapping somewhat. When the upper electro magnet 42B is provided with current, the magnetic field will move the valve body 2 in an upward

direction of the figure. Then, openings will be created along the entire edge lines between the annular edge portions 271A, 271B and 272A, 272B, respectively, so that oil may flow between the annular slots provided between the edge portions 104A, 271B and 103A, 271A, respectively, from the central annular chamber 151 and 260, respectively, up into the upper annular chambers 161 and 163, respectively. Herefrom the pressurized oil may then freely flow into the upper chamber 116 through the radial apertures 124 and then through the conduit 430 pressurize the return chamber 411 to the upper piston 400. Simultaneously, the corresponding slots 104C, 272A and 103C, 272B, respectively in the lower part open, whereby oil may flow out from the lower chamber 115 through the radial apertures 153 into and through the annular chamber 160, and either directly through the inner annular slot 160 or through the apertures 261 in the valve body 2 through the second annular slot 164 down into the lower annular chamber 162 and out through the outlet 119A to the tank. Thus, a instantaneous pressurization of the upper chamber 116 takes place, while a drainage of the lower chamber 115 is performed, so that oil may be pressed out through the conduit 520 from the working chamber 512 of the lower piston 500. As a consequence, both pistons 400,500 will be able to perform a return movement.

When the return stroke has been performed towards a certain return position, so that both pistons before the working stroke will get exactly the same impact length, the movement of the valve body 2 may be reversed by means of the lower magnetic device 42A, and an inverted pressurization and drainage, respectively, may take place so that the pistons 400,500 instead perform a working stroke. It should be noted that the unbroken, interacting edge lines, e. g. 104C and 272A, imply that an extremely small movement of the valve body 2 causes a large opening, i. e. that a large annular slot is formed so that large flows may be achieved.

According to the example the outer diameter D of the valve body is 100 mm, which at a movement of the valve body by only 1 mm gives a, in relation to the movement, very large through-flow opening. (The total area will be about 600 mm ( D x 71 x 2), as the edge portion gets all around.) It should be mentioned that the valve body 2 all the time is in the counter-balanced state, in the radial direction, as the radially exposed surfaces of the valve body in each chosen point are subject to a counter-directed radial force, which is equally great on the opposite side of the valve body 2. This is achieved thanks to the annular recesses which

are provided in a symmetrical manner around the valve body and to the openings in the valve body, which makes communication between said annular spaces possible.

With reference to Fig. 6, an impact machine is shown as an example, which machine is generally designated 31, and which is especially suitable to be provided together with a hydraulic device according to Fig. 1. Its main components consist of an upper impact unit 32; a lower impact unit 33; a central unit 34 ; an upper stand 36 consisting of a pair of upper rods 38 constituting a pair of piston rods ; and a lower stand 37 consisting of a pair of lower rods 39 also constituting a pair of piston rods. A foundation has been designated 35.

The upper impact unit 32 comprises a yoke 310 on the piston rods 38 and may be raised and lowered by means of a pair of upper, hydraulic lifting cylinder 312 being connected to the foundation 35, wherein the hydraulic chamber of lifting cylinders are filled with and emptied of hydraulic fluid through the hydraulic conduits extending through the piston rods 38 and the yoke 310 from and to a pressure source and a tank, respectively.

The yoke 310 supports an upper, hydraulic impact cylinder 410 connected to the yoke, which cylinder contains an upper ram in the form of an impact piston 400 (see Fig. 1).

An upper impact body is designated 315. Said body is movable in an upper impact body cylinder 316. An upper punch 317 is replaceably connected to the impact body 315. The upper impact body cylinder 316 is fixedly connected to the upper impact cylinder 313.

The lower impact unit 33 comprises a lower yoke 320 suspending in the rods 39 consisting of a pair of piston rods, which may be raised and lowered by a pair of lower, hydraulic lifting cylinders 322, which are also connected to the foundation 35, and which are filled with and emptied of hydraulic fluid through the hydraulic conduits through the piston rods 39 and the yoke 320 from and to a pressure source and a tank, respectively. The yoke 320 supports a lower hydraulic impact cylinder 510 connected to the yoke, which cylinder contains a lower ram in the form of an impact piston 500 (see Fig. 1). A lower impact body is designated 325. Said body is movable in a lower impact body cylinder 326.

The central unit 34 comprises a table 330, which may be movable in the horizontal plane but which in principle is fixed in the vertical direction, but means may be provided to allow a certain flexibility in the vertical direction. The means for movements in the horizontal plane and for damping/resilience in the vertical direction are only symbolically shown in Fig. 6 and are designated 331. The table 330 contains

and supports a number of identically similar, functional units 332. The main parts of the functional unit 332 shown in Fig. 1 comprise a lower, tubular punch 327 ; a die 334; a lower punch holder 336, which is slidably movable in a punch holder controller 337 ; and a mandrel 335.

The described equipment functions as follows. In a previous operation the die cavity has been filled with working material 90 around the mandrel 335. The working material 90 may constitute of a ring of metal, of polymer or of a composite material, which may include a ceram or any other mouldable material, but in this example it is presumed that the working material is a metal powder, possibly a composition of metal and ceramic powder. Initially, the upper yoke 310 is lowered by means of the upper lifting cylinders 312 and the piston rods 3 8 conveying the upper impact body cylinder 316 and its impact body 315 so far that the upper, tubular punch 317 is brought down to contact with the metal powder 90 in the moulding cavity and begins to compress the powder until the pressure reaches a certain predetermined value. The movement is stopped and the position is maintained.

The yoke 324 now begins to move upwardly by means of the lifting cylinders 322, whereby the lower punch is pressed upwardly against the powder 90. The movement continues until the pressure reaches a certain predetermined value. Said pressure is then also via the powder 90 transmitted to the upper impact unit. The powder 90 is hence pre-compressed and centered in the moulding cavity in the die 334.

The impact machine is now ready to consolidate the powder in a single, simultaneous stroke by the two rams 400 and 500 to form the desired article. Thanks to the device according to Fig. 1, it will be possible to perform two completely synchronized strokes for forming the powder 90. If a valve device according to Fig. 2 to 5 is used, extremely heavy forces/great accelerations are created.

The kinetic energies of the movable masses, which are very great, are transmitted through the upper punch 317 and the lower punch 327 to the powder 90. The rams 400 and 500 perform only one stroke, but the movement energies, which are essentially transmitted to the metal powder 90 in the moulding cavity, are so great that the powder is plasticized, whereby it is spread in the moulding cavity to form a consolidated body with the desired shape during some msecs.

It is realized that the invention is not limited to the above description but that it may be varied within the scope of the following patent claims. Thus, it is for instance realized that the impact machine according to Fig. 6 in many respects may be simplified/modified, for instance through eliminating the hydraulics to the impact bodies 315,325, which are not necessary for certain applications.