[0001] The invention relates to a control system with at least two channel-guiding parts and an intermediate plate arranged between the two channel-guiding parts. The intermediate plate comprises at least two flat metallic gasket layers as well as a screen layer arranged between the at least two facial metallic gasket layers. In the intermediate plate, one or several fluid passage openings are formed, which pass through the flat metallic gasket layers so that they form passage openings. These passage openings are spanned by the screen layer. The screen layer mainly serves as a filter to catch particles, which may not be carried over into the channel-guiding parts, as they there would cause blockings and functional failures. The screen layer is not intended to be a replaceable filter system but rather as a permanently installed element, which is used in addition to a further filter system in the total system which can be replaced and emptied. Such control systems are in particular control systems for hydraulic transmissions, in particular in vehicles.

[0002] Control systems comprising intermediate plates with screens are in principle already known from the state of the art. In EP 0 803 654 A2, a control system is disclosed, the intermediate plate of which consists in a carrier and a screen material. The screen material there in a continuous manner is tightly connected to the carrier via an elastomeric lip which was cured in place and this way continuously surrounds the individual openings of the carrier. This is however related to a considerable effort in production. In addition, practice shows that the construction with elastomeric lips and only one carrier plate is not able to permanently seal the control system in a reliable manner with the pressures given nowadays in hydraulic transmission systems.

[0003] Departing from EP 0 803 654 A2, DE 10 2007 019 946 enhances the solution of the former as it arranges metal sheet gasket layers on both surfaces of a continuous screen layer. Instead of the elastomeric lip, which in EP 0 803 654 A2 connects the screen to the carrier layer and which simultaneously serves as the sealing means, here two different kinds of sealing elements are used. On the one hand, the areas that are not used for the passage of fluids are filled with a sealing mass, in order to avoid transverse leakage. On the other hand, additional elastomeric sealing lips are provided on those surfaces of the metal sheet gasket layers which point away from the screen layer. Doing so, the production effort compared to EP 0 803 654 A2 is further increased.

[0004] DE 20 2010 006 768 Ul considerably simplifies the sealing concept. At the same time, practice shows that in relative large passage openings in the metal sheet gasket layers when exposed to either strongly pulsating pressures which pass the screen in only one direction or to fluids that pass the screen in both directions but with significantly different pressures in both directions, the screen areas affected by these flows are stretched in the passage direction, this way the open area of the screen is enlarged in the passage opening and therefore, it is no longer possible to catch all particles as required. With an even more extreme stretching of the screen layer in the area of the passage openings, the danger arises that individual threads of the screen break. In the worst case, the screen is not only no longer able to catch particles, but the sections of the thread chipped from the screen circulate themselves as contamination particles in the fluid circuit.

[0005] It is therefore the object of the invention to provide for a control system, the intermediate plate of which provides good sealing properties and at least one permanently stable and dimensionally stable filter area. In addition, the control system is to be produced with little expense.

[0006] The solution of this object is achieved with the control system according to claim 1. Preferred embodiments are described in the dependent claims.

[0007] The invention thus relates to a control system with at least two channel-guiding parts and an intermediate plate arranged between the two channel-guiding parts. The intermediate plate comprises at least two flat metallic sealing layers as well as a screen layer situated between the two flat metallic sealing layers. Flat sealing layers, for a better distinction from screen layers, are to be understood as layers which apart from the passage openings are continuous, thus in particular metal sheet layers. The control system comprises a plurality of passage openings for fastening means, which pass through the at least two channel-guiding parts and all layers of the intermediate plate, while the intermediate plate comprises at least one fluid passage opening, which passes through the at least two flat metallic sealing layers and which is spanned by the screen layer. A fluid passage opening is to be understood as such an area, which in each of the two channel-guiding parts abutting to the intermediate plate individually opens out to an individual opening or an individual channel. In order to guarantee a permanently durable filtering area even with a huge and one-sided pressure load, at least one support arrangement for the screen layer is formed in at least one of the fluid passage openings in the flat metallic sealing layer adjacent to the screen layer.

[0008] The support arrangement is always formed as a protrusion protruding into the fluid passage opening in a flat metallic sealing layer adjacent to the screen layer. The support arrangement may simply protrude into the fluid passage opening or be formed as a bridge linking two edges of a fluid passage opening and dividing the latter in the respective flat metallic sealing layer. The at least one protrusion does not form a separate or separately-formed part, but continues from the respective flat metallic sealing layer or its edge and is thus one-piece with the respective flat metallic sealing layer. [0009] When a fluid passage opening the area of the sealing layer is cut by a bridge and divided into two parts, it is nevertheless considered as a single fluid passage opening if it continues in a single channel both up- and downwardly. Even a one-sided continuation in only one single channel is sufficient in order to consider a fluid passage opening which is divided in such a way as a single fluid passage opening.

[0010] In a first embodiment, the at least one fluid passage opening is formed as a rounded convex polygon comprising n corners of a polygon. A rounded convex polygon is to be understood in such a way that the corners of a convex polygon are rounded as one generally has to work with laterally rounded stamps when punching openings into metal sheet layers in order to achieve an acceptable service time of the tool. This causes rounded corners in the part, too. The radii usually used in this respect are between 0.3 and 1 mm. The n corners of a polygon are thus no real sharp corners but are to be understood as virtual corners, which result in the intersection points of lines which continue the sides of the polygon without regard to the rounding. This is also valid for the further polygonal fluid passage openings which will be mentioned in the following paragraphs.

[0011] At the convex-polygonal fluid passage opening of this first embodiment, the at least one support arrangement is formed in at least one flat metallic sealing layer adjacent to the screen layer. It is preferably formed as a protruding bridge which protrudes from the edge or from two different edge sections of the fluid passage opening which edge sections are distanced to each other. The protruding bridge divides the polygon and intersects at least one diagonal of the polygon, which diagonal links two corners of the polygon. With higher polygons, thus polygons with a larger number of corners, it is preferred that the two corners of the polygon are not immediately adjacent corners. It is rather preferred that with an even number n of corners of the polygon, they are distanced to each other by n/2 corners of the polygon and with an uneven number n by n/2 + ½ corners of the polygon. This way, it is ascertained that the bridge provides a good support of the adjacent screen layer.

[0012] Although most of the embodiments referring to a bridge as the basic form of the support arrangement use the term "bridge" in the sense of an element linking two edges, the term also includes the term "bridge" in the sense of a "boat bridge" meaning that it has one free end. The other end is a one-piece protrusion from the edge of the fluid passage opening.

[0013] It is particularly preferred if the at least one bridge of the at least one support arrangement does not only cross one such diagonal of a polygon, but a minimum number of such diagonals of polygons, which result from rounding of n/3 if n is uneven and of n/6 if n is even. The difference results from two diagonals coinciding pairwise with n being even. [0014] The term rounded-convex polygon also includes a circle as an extreme shape if n tends towards infinity. As a preferable support arrangement for the screen layer in the area of a round fluid passage opening, one can thus use a bridge, which links two edges of the round fluid passage opening in a flat metallic sealing layer adjacent to the screen layer. With respect to the position of the bridge, one can consider different shapes of bridges. On the one hand, these are bridge shapes which in their course have a variation of their width by a factor which is at the most 2. Here, the adjacent transition points between the bridge and the actual circle are distanced to each other by at least 120° of the circumference of the circle. On the other hand, these are bridge shapes which in their course have a variation of their width by a factor larger than 2, thus which in particular broaden in their outer region, thus adjacent to their transition to the actual circle. Here, it is sufficient if the adjacent transition points between the bridge and the actual circle of both edges of one bridge are distanced to each other by at least 90°.

[0015] If one instead of the aforementioned transition points considers a line where the bridge has half its width and where this center or middle line of the bridge intersects with a virtual continuation of the circumference of the circle, then these two points in the former case - variation of the width of at the most 2 - are distanced to each other by at least 150° of the circumference of the circle, in the latter case - variation of the width of more than 2 - by at least 120°.

[0016] With an oval as an extreme shape of a rounded-convex polygon as the shape of the fluid passage opening, a comparable situation results.

[0017] If the at least one fluid passage opening is however rounded-concave polygonal, thus if at least one corner of the polygon faces inwardly and if this polygon shows at least one constriction, then the support arrangement is preferably formed as a bridge protruding from the edge of the fluid passage opening, which spans the constriction and this way divides the fluid passage opening. Again, this at least one support arrangement is formed in a flat metallic sealing layer adjoining to the screen layer.

[0018] With elongate fluid passage openings, it is of course also possible that more than one bridge is provided as support arrangement for such a fluid passage opening. With convex-polygonal fluid passage openings, a plurality of bridges is advantageously arranged in such a way that what has been laid out before shall now be valid for an area which extends between bridges which are not immediately neighboring bridges, but which are distanced to each other by one bridge or between an edge of the fluid passage opening and one but the next bridge. Here, the individual bridges are arranged one next to another and in their main extension direction differ from each other by at the most 45°. With concave-polygonal fluid passage openings, the bridges in oblong fluid passage openings or multiply angled fluid passage openings as in the concave-polygonal fluid passage openings already described are preferably formed in the area of constrictions.

[0019] A further embodiment of the invention results with essentially circular fluid passage openings if the support arrangement for the screen layer is a protrusion extending from the edge of the fluid passage opening in one of the flat metallic sealing areas. This at least one protrusion in this flat metallic sealing area extends by at the most 1/3 of the circular diameter of the fluid passage opening from the virtually continuing circumferential circle into the area surrounded by the virtually continuing circumferential circle.

[0020] This embodiment of the support arrangement in a control system according to the invention comprises two to eight protrusions. The individual protrusions are distanced to each other. In particular, the individual protrusions are distanced by at least 15°, preferably at least 20° of the circumference of the virtually continuing circumferential circle. However, at least 1/3 of the circumference of the virtually continuing circumferential circle is preferably present not only virtually but as a real circumferential circle, this at least 1/3 of the circumference in most cases is divided into sections by the protrusions and defines the actual virtually continuing circle.

[0021] Independent of the basic shape of the fluid passage opening, one of the embodiments of the support arrangements for the screen layer provides that the support element consists in a protrusion extending from the edge of the fluid passage opening in a flat metallic sealing layer adjoining to the screen layer. This protrusion reduces the passage surface of the fluid passage opening in this flat metallic sealing layer adjoining to the screen layer by between 5 and 20% compared to the passage surface of the fluid passage opening without this protrusion. The reduction can also be measured by comparison with the fluid passage opening in the flat metallic sealing layer opposite to the screen layer, if one compares the passage surface on the one side of the screen layer which is reduced by the protrusion with the passage surface of the continuing passage opening on the other side of the screen layer.

[0022] In general, it is advantageous for the control system if the at least one fluid passage opening in at least one of the flat metallic sealing layers is surrounded by at least one sealing means. Preferably, this sealing means is provided in one of the flat metallic sealing layers adjoining to the screen layer. A further improvement results if such a sealing means is provided in both flat metallic sealing layers adjoining to the screen layer or if both sealing layers facing the channel-guiding parts comprise such sealing means. If the fluid passage opening in one of the channel-guiding parts adjoining to the intermediate plate does not open out into an opening but into a channel or a section of a channel, which extends in the interface between the intermediate plate and the channel-guiding part over a length larger than four times its width, then it is advantageous if a sealing means formed on the side of the flat metallic sealing layer facing the channel-guiding part does not only surround the passage opening in a continuous manner but continuously also surrounds the channel or the channel section in the adjacent channel-guiding part.

[0023] It is advantageous if the sealing means is a bead formed into one of the flat metallic sealing layers. The bead may be realized as a full bead with an approximately U-shaped or tub-shaped cross section or as a half bead with an approximately flat z-shaped cross section. It is however preferred if the bead is formed as a complex bead system which extends in the layer of the flat metallic sealing layer with forks and crossings. In the fork and crossing areas, the full beads may then pass into half beads and vice versa. In particular towards the outer edge of the intermediate plate, the complex bead system is closed meaning that a sealing line extends distanced to and along the outer edge of the intermediate plate. Preferably, the complex bead system also comprises sections in the inner area of the intermediate plate which are self-contained. These are in particular such sections which surround passage openings and in cases in a continuous manner channel sections continuing from passage openings.

[0024] As an alternative or as a supplement to the former, the sealing means may be a polymer- based coating which is applied to at least one of the surfaces of at least one of the flat metallic sealing areas in particular in sections in a pattern. Here as well, the coating pattern is preferably complex with forks and crossings and in addition to a self-contained line which surrounds the outer edge with a distance comprises further sections, which are self-contained, too, and which surround passage openings and in cases channel sections continuing from these. In a first variant, the partial coating is thus the only sealing means. In a second variant, the beads are or the complex bead system is covered at least in sections at least on one of its surfaces with a coating. In this respect, it is advantageous if the coatings protrude over the lateral edge of the actual bead area, e.g. by about or exactly half a bead width or by an entire bead width to both sides. In principle, it is also possible if one of the flat metallic sealing layers adjoining to the screen layer comprises sections, in which coated or non-coated beads are formed as sealing means in these sections and which in addition comprise sections, in which a partial coating on one or both surfaces represents the only sealing means in those sections.

[0025] In addition to the beaded and/or coated sealing layers, which in the following will also be referred to as active layers, the intermediate plate may also comprise one additional sealing layer, which apart from the passage openings does not comprise any structure and which either comprises no coating or on at least one of its surfaces is coated essentially completely with a polymer-based coating comparable to the partial coating of the active layer(s) or with a metal-based coating, such as a zinc plating. "Essentially completely" in this context is to be understood in such a manner that the edges of the passage openings may, but must not, be left out from the coating or that the coating is removed from these edges of the passage openings, so that during operation no particles of the coating are set free, which then would form an additional load for the screen sections of the intermediate plate. This non-structured additional sealing layer is often referred to as distance layer as it is one of its tasks to adapt the total height of the intermediate plate to the installation situation. It further serves, especially with beaded active layers, for the decoupling of the sealing lines of the active layers arranged directly or indirectly on its surfaces, as it usually comprises a sufficient thickness and stiffness against bending. In the following, this non-structured sealing layer may also be referred to as distance layer.

[0026] For the partial coatings, one preferably uses coating materials which comprise FKM (fluoro- elastomers, such as vinylidene fluoride-hexafluoropropylene copolymers), silicone elastomers or NB rubber (nitrile-butadiene rubber), HNBR (hydrated nitrile-butadiene rubber), PUR (polyurethane), NR (natural rubber), FFKM (perfluoro- elastomers), SBR (styrene-butadiene rubber), BR (butyl rubber), FVSQ (fluoro silicone), CSM (chloro-sulfonated polyethylene), silicone resin and/or epoxy resin or mixtures of the aforementioned materials. Preferred coating thicknesses range between 15 and 60 μιη, in particular between 20 and 40 μιη.

[0027] In a further embodiment, the partially applied polymer-based coating is a foamed coating, which is characterized by a particularly high elasticity and ability to adapt to shapes. It is preferred if these foamed coatings are based on NBR or FKM.

[0028] The control systems according to the invention only in scarce situations in all fluid passage openings show a fluid stream only from a first surface of the intermediate plate to the opposite, second surface of the intermediate plate or from the first channel-guiding part to the second channel-guiding part only. Rather, in most situations, they comprise fluid passage openings through which a fluid stream from the first to the second surface is given as well as fluid passage openings through which fluid flows from the second to the first surface of the intermediate plate. In this case, the intermediate plate comprises at least two fluid passage openings, which each comprise a support arrangement, with the two support arrangements being realized in different flat metallic sealing layers, which are both adjacent to the screen layer, but adjoin to the latter from opposite surfaces. Thus, the intermediate plate comprises at least one support arrangement for a screen layer section, where fluid passes from the first to the second surface with the support arrangement being realized in the flat metallic sealing layer which abuts to the screen layer and points towards the second surface of the intermediate plate. This preferred embodiment comprises at least one support arrangement for another section of the screen layer, in which section the fluid flows from the second to the first surface of the screen layer; here, the support arrangement is accordingly realized in the flat metallic sealing layer which adjoins to the screen layer and points towards the first surface of the intermediate layer.

[0029] In addition, fluid passage openings may be present in which the fluid dependent on the operational and switching condition flows in the one or in the other direction. In particular if the fluid stream in at least one of the directions is realized with a high pressure, it can be advantageous in this variant, if on both sides of the screen layer in the respective adjacent flat metallic sealing layer a support arrangement, in particular a bridge-shaped support arrangement, is provided. The two, in particular bridge-shaped support arrangements overlap in a projection into the plane of the screen layer at least in sections, so that they reduce the flow cross section to an acceptable degree only. It is preferred if they overlap with their entire area, so that independent of the flow direction a good support of the screen is given without a further reduction of the flow cross section.

[0030] The screen layer is preferably formed from a mesh material. A mesh material in the sense of this invention includes not only a knitted fabric, a stitch-bonded fabric, a roving or a crocheted fabric but in particular a woven material. In this context, plain or twill weaves are preferred. In addition to a non-treated woven material, a woven material which has been compressed at least in sections can be used as well. Among the compressed woven materials, calandered woven materials are particularly preferred as they are easy to produce. The compression or calendaring of the mesh material causes a reduction of the thickness of the material in the direction orthogonal to the plane of the screen material. With this compression, the thickness of the mesh material of the screen layer can be reduced by 25 to 70%, preferably by 35 to 55 % relative to its original thickness. The thickness of the thread after the compression in its shortest extension direction has to be at least 30 μιη in order to avoid a destruction, e.g. a break, of the mesh material. Higher thread thicknesses, e.g. about 55 to 150 μιη and in particular 70 to 90 μιη are therefore preferred. As an alternative, the screen layer may also be produced from a flat material which has been provided with holes, e.g. by etching, or by stretching the material as for a tanged steel. The diameter of a hole here ranges from 120 to 200 μιη, preferably from 120 to 150 μιη. The distances of the holes are particularly selected in such a way that an open area of > 30%, preferably of > 35% results.

[0031] If the screen layer consists in a woven material, then this woven material preferably shows a mesh width of 100 to 250 μιη. Particularly advantageous screens both with respect to pressure drop and the size of the particles retained in the screens have a mesh width of 120 to 160 μιη.

[0032] A first preferably variant provides that the mesh material is a mesh material from synthetic fiber, where a large variety of fibers are suited. These comprise polyester (PES), in particular poly- butylene terephthalat (PBT) and polyethylene terephthalat (PET), polyamide, in particular aramide (AF) and aliphatic polyamide, phthalic anhydride (PSA), polyphthalamide (PPA), polyphenylene sulfide (PPS), polyimide (PI), polyetherimide (PEI), polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), polysulfone (PSU), polyacrylonitrile (PAN), polyamide-imide (PAI). In addition carbon fibers (CF) and glass fiber can be used, both as independent fibers or as reinforcement for the above-mentioned fiber materials or for polyethylene (PE), polypropylene (PP), polystyrene (PS), polycarbonate (PC), poly(methyl-methacrylate) (PMMA), epoxy resin fiber materials or fiber materials based on unsaturated polyesters (UP). With respect to the individual fiber, compounds, copolymers and blends from the materials mentioned above can be used, too. With woven materials, it is further possible to use different fibers as warp and weft thread.

[0033] Particularly preferred are woven materials from PTE, most preferred are woven materials using PET monofilaments both as warp and weft threads.

[0034] It is preferred if the synthetic fiber mesh shows a tensile strength both in the warp and weft direction of 80 to 150 N/10 mm, advantageously of 100 to 120 N/10 mm according to DIN EN ISO 13934.

[0035] In contrast, in a second advantageous variant, the screen material is a metallic mesh material, in particular a steel mesh material. It is particularly preferred if a metal thread with a tensile strength of 500 to 900 N/mm ² - including or excluding the limits - is used. Here, the tensile strength is derived from the standard for the respective metal material. The screen material does not show a coating over its entire area, which fills the meshes. However, the thread of the mesh material may be coated in sections or completely. It is essential in this respect that the meshes remain open over the entire surface of the screen layer.

[0036] The flat metallic sealing layers may be produced from different materials. Given the higher tensile strength, sealing layers made from steel are preferred, thus sealing layers made from carbon steel or from spring steel. Spring steel is particularly advantageous for beaded active layers, but carbon steel is suited for this application, too. The layer thicknesses for active layers preferably range between 0.15 and 0.3 mm, including these limits. For distance layers, especially for thicknesses of at least 0.5 mm, metal sheets from aluminum or an aluminum alloy are used. As the flat metallic sealing layers are preferably only partially coated with a polymer-based coating, materials which are resistant against corrosion are particularly preferred, e.g. stainless steel or zinc-plated steel.

[0037] As to the general design of the intermediate plate, several possibilities exist, the application of which depends on the application and in particular on the course of the channels and the situation of the fluid passage openings in the channel-guiding parts.

[0038] If the fluid openings and courses of the channels are rather similar in both channel-guiding parts adjoining to the intermediate plate, it is possible to provide for identical or essentially identical courses of the sealing means on both surfaces of the intermediate plate. To this end, it is preferred if the intermediate plate comprises exactly two flat metallic sealing layers, thus two active layers, and a screen layer arranged between them. With such an arrangement, a steel metal sheet is preferably used for the two flat metallic active layers.

[0039] If the courses of the channels and the positions of the fluid passage openings in the two channel-guiding parts adjoining to the intermediate plate are rather different, then different courses of the sealing means can scarcely be avoided. In this situation, it is preferred if the intermediate plate comprises at least one distance layer, which is sufficiently thick and resistant against bending so that the sealing lines on both surfaces of the intermediate plate, thus the lines along which the screw forces are introduced as line pressure into the sealing layer and between the channel-guiding parts and the intermediate plate, are decoupled against each other. Here, it is thus advantageous if the intermediate plate comprises at least three flat metallic sealing layers and a screen layer arranged between them so that an active layer on the first outer side is followed by a distance layer, further by a screen layer and even further by a second active layer on the other outer side. This allows for a flexible adaptation of the total thickness of the intermediate plate. As in the preceding example here again, at least one, but preferably two sealing layers, in particular active layers, consist in steel. The third layer, thus in particular the distance layer, may be produced from steel, aluminum or an aluminum alloy.

[0040] Prior to mounting the multi-layer intermediate plate between the channel-guiding parts, the layers of the intermediate plate are preferably connected to each other using methods of the state of the art as they are known in the context of metallic flat gaskets, e.g. by welding, riveting and/or clinching or by other positively fitting connection methods.

[0041] In addition to the completely open passage openings for fastening means, the intermediate plate of the control plate according to the invention may comprise further completely open passage openings, in particular for fluids, which do not need any filtering. In these completely open passage openings, the screen layer is left out, too.

[0042] The control system according to the invention finds its applications in particular in vehicles, in particular as control system for transmission systems, in particular for hydraulic transmission systems. In these applications, the screen layer retains abrasion particles in the oil circuit.

[0043] In the following, the invention shall be explained by reference to some drawings. These drawings only serve for the illustration of preferred embodiments without the limitation of the invention to these embodiments. In the drawings, identical reference numbers denote identical parts. The illustrations have schematic character, thus they neither have to be to scale nor correspond to standards of technical drawings. In contrast, in order to emphasize details, the illustration of edges situated in the background and the like has been dispensed with.

[0044] The drawings show schematically:

Figure 1: A control system according to the state of the art in three partial views;

Figure 2: A first embodiment of a control system according to the invention in five partial views;

Figure 3: Three possible layering designs of intermediate plates in control systems according to the invention;

Figure 4: A top view to an intermediate plate of a control system according to the state of the art;

Figure 5: A second embodiment of a control system according to the invention in three partial views;

Figure 6: A top view to a third embodiment of an intermediate plate of a control system according to the invention as well as a detailed view;

Figure 7: A fourth embodiment of a control system according to the invention in three partial views; and

Figure 8: Examples of the design of bridges in intermediate plates of control systems according to the invention.

[0045] Figure 1 shows a control system according to the state of the art, partial Figure 1-a provides a top-view of the intermediate plate 101 of the control system. Partial Figure 1-b in a sectional view shows sections of the two channel-guiding parts 102, 103 as well as of the intermediate plate 101 arranged between them. The section shown in Figure 1-b with respect to the intermediate plate 101 corresponds to the section A-A in Figure 1-a. Figure 1-c is focused on the intermediate plate 101 only and shows the area of the intermediate plate 101 highlighted with a dotted line frame in Figure 1-b in detail.

[0046] From Figure 1, it becomes clear that the intermediate plate 101 comprises a plurality of passage openings, where the passage openings 113 for fastening means, via which the intermediate plate 101 is connected to the channel-guiding parts 102, 103 or through the latter at additional parts, and the passage openings 111, 112 for fluids can be distinguished from each other. The fluid is prevailingly hydraulic fluid, thus usually hydraulic oil. Some of the passage openings for fluid, namely the fluid passage openings 111, are additionally spanned by a screen, which has a mesh width which is sufficiently large for the passage of the fluid, but sufficiently small in order to retain particles carried in the fluid. These are in particular particles, which during early operation stages of a new transmission can be released and which in no case may be carried over to valves, sliding pistons or the like, as they are able to block them. In addition, the intermediate plate 101 comprises a plurality of fluid passage openings 112, which work without any screen. Here, the screen layer 104 has been left out accordingly. Dependent on the volume of fluid that has to pass and on the shape of the openings in the adjoining parts, the fluid passage openings 111 may have different shape, as is illustrated on the example of three different fluid passage openings 111 with screen. The fluid passage opening 111a shows a rounded rectangular shape, the longitudinal extension here is more than twice the extension in the widthwise direction. It can thus be considered as a convex polygon with the number of corners being n=4. The fluid passage opening lib also shows rounded corners and can be considered as a concave polygon with n=8 corners. The concave shape of this polygon causes that this polygon shows a constriction. The fluid passage opening 111c is a circular opening, which can also be considered as a polygon with an infinitive number of corners.

[0047] In the top-view of Figure 1-a, two protruding areas are highlighted in which elements 114 are arranged, which serve for the connection of the individual layers of the intermediate plate 101 to each other. In addition, a web of beads 163 branched in many ways is visible on the surface facing the spectator; a second web of beads branched in several ways appears with dotted lines on the surface of the intermediate plate 101 pointing away from the spectator. Both bead systems serve for the sealing of the fluid passage openings. Although the same hydraulic fluid passes through the different fluid passage openings, they have to be sealed against each other as the hydraulic fluid in different fluid passage openings or in channel sections branching off from these have different pressure and/or different flow velocity in order to control sliding pistons, valves and the like. In the same way, the intermediate plate needs to be sealed to the outside.

[0048] Partial Figure 1-b illustrates how the two channel-guiding parts 102, 103 continue the channels 120, 130 through the intermediate plate 101. In the example given, the channels in the upper channel-guiding part 102 predominantly flow transverse to the drawing plane, while in the lower channel-guiding part 103, both in the right and the left section of the drawing, channels 130 extending in the drawing section are shown, which through the intermediate plate 101 connect several of the channels 120 of the upper channel-guiding part 102.

[0049] Both from the sectional view of partial Figure 1-b and from the section of the intermediate plate 101 given in partial Figure 1-c, it becomes clear that the screen layer 104 is arranged between the upper active layer 106 and the distance layer 105 and that a further active layer 107 is installed below the distance layer 105. The upper and lower active layers 106, 107 each comprise beads 163, 173, which run adjacent to the fluid passage openings 111, 112 and this way provide for their sealing. Figure 1-b illustrates that only in those areas where the respective area of the intermediate plate rests on a channel-guiding part, beads are realized.

[0050] As already mentioned, some of the fluid passage openings, namely the fluid passage openings 111, comprise screens 104, other fluid passage openings, namely the fluid passage openings 112, function without such screens. If fluid passes through the fluid passage openings 111, which are spanned by a section of the screen layer, then the section of the screen layer 104 which covers the corresponding fluid passage opening 111 is loaded with pressure; the load is the higher the higher the fluid pressure is and the more it pulsates. As a consequence, the mesh material of the screen layer 104 is stretched, and the mesh material bulges over the plane, which it spans in the other areas between the flat metallic layers 105, 106 of the intermediate layer 101. This effect is increased if the fluid in a particular fluid passage opening 111 does not always flow in the same direction or rests, but if it dependent on the operational state rests in this fluid passage opening 111 or flows in the one or the other direction. With each change of direction, the affected section is flipped from the plane between the flat metallic layers 105, 106 arranged adjacent to the screen layer 104 and during this flipping encounters a line-shaped compression at the circumferential edge of the passage opening 111 in the respective sealing layer 105, 106, in particular in its edge section, where it rests against the adjacent flat metallic sealing layers 105, 106.

[0051] Under permanent operation with frequent load alternations, this alone can lead to wear of the mesh material and to the breaking of individual threads or wires. Once several threads or wires have been separated, then pressing of the cut-off edge region towards both directions is facilitated and continued breaks of the vicinal threads or wires are enhanced. One of the consequences of this is that no particles can adhere in the respective passage opening 111 and the screen layer 104 therefore can no longer pursue its actual task. Even worse, individual treads or wire sections can be cut off, which then are carried along in the fluid circuit and which then can themselves block sliding pistons, valves and the like.

[0052] This effect increases if excessive burrs, such as punching burrs are given at the edge of the fluid passage opening 111 in the adjacent gasket layers. These punching burrs are formed in the respective metal sheet while the passage openings are punched out, especially on the side of the metal sheet, which is opposite to the entrance side of the tool.

[0053] This cannot be accepted in hydraulic control systems. The invention counters this in that at least one support arrangement is provided in one of the flat metallic sealing layers adjoining to the screen layer, which support arrangement prevents the bulging and stretching of the screen layer. Figure 2 illustrates this on the example of a control system according to the invention. The top-view of Figure 2-a shows an intermediate plate 1 which in principle can be compared to the intermediate plate 101 shown in Figure 1-a, but which at particularly charged passage openings 11, e.g. at the constriction position 47 comprises bridges 41, which protrude from the edge of the passage opening 11 and bridge the later. The channel-guiding parts 2, 3 in Figure 2 correspond to the channel-guiding parts 102, 103 in Figure 1, also with respect to the position and size of the passage openings and channels 20, 30.

[0054] The arrangement and design of the support arrangement for the screen-layer sections is illustrated in detail in the following partial drawings of Figure 2. From Figures 2-b and 2-c, which relate to section B-B in Figure 2-a, it becomes clear that the passage opening 11 which is located further to the left is only charged with small pressures and/or no changes in the passage direction of the fluid and therefore requires no additional support. The passage opening 1 located more to the right than the passage opening 11, which in Figure 2-a is referred to as passage opening 11a in order to mark its shape, is also bridged by a screen. Other than the passage opening 11, it is faced with a high pressure load from below to above as well as changes of the passage direction, with the pressure, when the fluid is flowing downward being considerably smaller than the pressure resulting from upward flow direction. In order to prevent from a destruction of the screen layer 4 in the area of this fluid passage opening 1 , it is spanned by a bridge 4 in the flat metallic sealing layer 6 arranged behind the screen layer 4 with respect to the main flow direction, with the bridge linking the two lateral sides of the passage opening 1 at a bout half the longitudinal extension of the passage opening 11'. The bridge 4 shows a width that corresponds to approximately 1/6 of the longitudinal extension of the passage opening and therefore does not excessively reduce the passage area. Although the passage opening 11' in the area of the sealing layer 6 is cut by a bridge and divided into two parts, it is nevertheless considered as a single passage opening, as it, as is illustrated in Figure 2-b, continues in a single channel 20 or 30, respectively, both up- and downwardly. Even a one-sided continuation in only one single channel is sufficient in order to consider a passage opening, which is divided as described above as a single fluid passage opening 11.

[0055] While the bridge 41' in Figure 2-b seems like a complete cover of the fluid passage opening 11', it becomes clear from Figure 2-d which shows a section orthogonal to the section in Figure 2-b, namely section C-C of Figure 2-a, that the bridge 41' covers the fluid passage opening 11' only in sections. Figures 2-d and 2-e further show that the screen layer 4 in the passage opening 11" on its bottom side is also prevented from an excessive deformation by a bridge 41" which adjoins to the former in sections. This bridge 41" in the top view of Figure 2-a is covered by the screen layer and therefore not visible. During operation of the control system a strongly pulsing fluid stream charges the screen downwardly, which means that operational states with immobile fluid alternate with a large downward fluid stream. The bridge 41" here is formed in the distance layer 5, while the bridge 4 of the passage opening 1 is formed in an active layer. While the distance layer 5 shows an higher material thickness, the active layer 6 shows a higher deformation stiffness and higher deflection, so that the bridges 4 and 41" with comparable size of the fluid passage opening and comparable pressure load can be designed with approximately the same width. It is always essential that the support arrangement is formed in the sealing layer 5, 6, 7 immediately adjacent to the screen layer 4.

[0056] The notation with the apostrophes 11, 11', 11" and 41, 41', 41", respectively, in Figure 2 only serves for the marking of the different passage openings and support arrangements, respectively, which are considered but it is not meant to distinguish between their function or delimit them to their function. From the sectional views of Figure 2, it further becomes clear that the channels 20, 30 in both cannel-guiding parts as well as the sealing elements, thus here the beads 63, 73, have very different courses. This requires a suitable choice of the basic construction of the intermediate plate with respect to the pressures of the fluids to be sealed against each other, namely with a decoupling of the sealing beads 63, 73 using a distance layer 5.

[0057] Figure 3 serves for the illustration of possible general constructions of the intermediate plate 1 of control systems according to the invention without explanation of the design of the support arrangement essential for the invention. Figure 3-a shows the construction of an intermediate plate 1 with a total of three flat metallic sealing layers 5, 6, 7, thus metal sheet layers as well as one screen layer 4. The bottom side of the upper channel-guiding part 2 adjoins to a first active layer 6, the distance layer 5 is arranged below the latter. The screen layer 4 adjoins to this distance layer 5, the second active layer 7 is located between the screen layer 4 and the lower channel-guiding part 3. The active layers 6, 7, comprise beads 63, 73, the heads of which point towards the channel-guiding parts 2, 3. The beads 73, 63 surround the passage openings 11 and in cases the channels 20, 30 in the channel-guiding parts 2, 3. On each of the beads, on their surfaces pointing towards the channel- guiding parts 2, 3, coatings 64, 74 have been applied, e.g. by screen printing. The coating does not only cover the respective bead but also the area adjacent to the feet of the beads which means that the total width of the coating corresponds to slightly more than 1.5 times the actual width of the bead. It also becomes clear from this illustration that the coating does not reach until the edge of the passage opening 11. Although in Figure 3-a the beads 63 of the upper active layer and the beads 73 of the lower active layer 7 in the section shown are situated one above the other, they extend differently at other positions. For this reason, a distance layer 5 is provided between the active layers 6, 7 here, which provides for a decoupling of the sealing elements so that they can be compressed independent of each other. [0058] In contrast, the constructions in Figures 3-b and 3-c are better suited for intermediate plates, in which the bead systems 63, 73 of both active layers run essentially parallel so that they rather reinforce their respective sealing effect, but are not able to decouple the sealing lines. In both constructions, the screen layer 4 is enclosed between two active layers 6, 7, which as in Figure 3-a with their heads of the beads point towards the channel-guiding parts 2, 3. While the active layers 6, 7 in Figure 3-b use beads 63, 73 as the sealing means, partial coatings have been applied in the construction of Figure 3-c in each case , which surround the passage opening 11 or a channel 20, 30 on that surface of the active layers 6, 7, respectively, which face the channel-guiding parts. In all drawings, not only in Figure 3, an explicit illustration of optional full-area coatings, e.g. on the distance layer 5 or on the surfaces of the active layers 6, 7, pointing away from the channel-guiding parts 2, 3 has been dispensed with.

[0059] Figure 4 shows a top view to an edge section of a further intermediate plate of the state of the art. In addition to a passage opening 113 for fastening means, a round fluid passage opening 111c can be identified which is surrounded by a bead 163. Here again with strongly pulsing fluid loads, the risk of overstretching and destruction of the section of the screen layer 104 bridging the fluid passage opening is given.

[0060] Figure 5 shows an edge section of an intermediate plate of a control system according to the invention, comparable to the one shown in Figure 4, where two protrusions 42 are provided at the edge of the fluid passage opening 11 as support arrangement for the screen layer 4. The pulsing fluid stream here shows its main flow direction upwardly, so that the protrusions, as can be seen in Figure 5-c, on the upper side of the screen layer 4 protrude into the area continuing the fluid passage opening 11 and this way also protrude into the area of the channel 20 in the upper channel-guiding part 2. In a projection into one common plane with the fluid passage opening 11, these two structures overlap with each other. The beads of the two active layers 6, 7 here show a comparable course over the entire intermediate plate, in the section shown in Figure 5 even a parallel course. Therefore, no decoupling of the beads 63, 73 is necessary, so that neither a distance layer nor a coating of the beads 63, 73 and of the laterally adjoining areas is provided. The construction in Figure 5 therefore corresponds to the one in Figure 3-c.

[0061] In Figure 6, a further inventive variation of the section of the intermediate plate shown in Figure 4 is shown. Here, at the edge of the generally round fluid passage opening 11, three regularly arranged protrusions 42 are provided as support arrangement to avoid an excessive stretching of the screen layer 4. The protrusions each project to a bit less than 1/3 of the diameter 48 of the actual fluid passage opening 11, which is delimited by the dotted line 40, into this opening and this way prevent from an overstretching or destruction of the section of the screen layer in the passage opening 11.

[0062] Figure 7 illustrates a further embodiment of a control system according to the invention. Here, the intermediate plate 1 consists of two active layers 6, 7 and a screen layer 4 located between them. The active layers 6, 7 on their surfaces pointing towards the channel-guiding parts 2, 3 each have partial coatings 65, 75 as sealing means. The entire section shown is charged with strong pulsing of the control fluid, so that all fluid passage openings 11, which here do not show individual reference numbers, are provided with support arrangements for the screen layer 4. The section of the intermediate plate 1, which corresponds to area D in Figure 7-a, is shown in detail in Figure 7-b, the one corresponding to section E in Figure 7-c. The passage opening located most left is charged with extremely strong pressures in both flow directions and frequent changes in the direction of the control fluid, so that here, the support arrangement consists in bridges 41*, which are located on both sides of the screen layer 4. With this, a stretching of the screen section in both directions is avoided, so that it can permanently fix particles. The both-sided bridges 41* here show the same extension.

[0063] Running further along the course of the intermediate plate 1 in Figure 7-a towards the right, then a section follows in which a channel 20 in the upper channel-guiding part 2 is covered by both flat metallic layers 6, 7 of the intermediate plate and safely surrounded by the coating sections 65 of the active layer 6. The screen layer 4 in this area has no filter function as it is covered, but continues between the active layers 6, 7. This both facilitates the production of the screen layer and self- stabilizes the screen layer. Further to the right, a fluid passage opening follows, which compared with the other fluid passage openings shown in Figure 7 is only charged with mild pulsing so that protrusions 42 as support arrangement for the screen layer 4 are only provided in the upper active layer 6. As in Figure 6, three protrusions 42 may be given, but only one of them can be identified in the sectional view.

[0064] Even further to the right in the course of the intermediate plate 1 in Figure 7-a and therefore on the left hand side in the detailed view in Figure 7-c, a passage opening follows which is faced with stronger pulsations than the ones described last, with the high fluid pressures being however only given with upward flow. Therefore, one bridge 41 on the upper surface of the screen layer 4 is sufficient as support arrangement for this screen section. The screen 41 extends essentially orthogonal to the double bridge 41* of the fluid passage opening 11 given to the most left in Figure 7-a.

[0065] The next fluid passage opening, the middle one in Figure 7-c in total shows a larger area than the one described before in the context of Figure 7. The screen section shown here is faced with strong pulsations between a high downward fluid pressure and a somewhat smaller upward fluid pressure. To face this, but in order not to excessively loose passage area, here a double bridge 41*, thus bridges on both sides of the screen layer are provided on the right-hand side, and a small simple bridge 41 is provided on the left hand side. On the bottom side of the screen layer 4, thus on the surface requiring a better support, two bridges are given this way, while a simple bridge being part of the double bridge 41* is sufficient on the top side of the screen layer 4.

[0066] The fluid passage opening situated extremely right is only charged with medium pressures in the upward direction, but shows a very large passage area, so that possible deformations and destructions of the corresponding screen section are prevented from by the arrangement of a bridge 41 as support arrangement on the upper side and immediately behind the screen layer 4.

[0067] In two partial drawings, Figure 8 shows two embodiments for the design of the bridge in a flat metallic sealing layer adjacent to the screen layer, in particular in an active layer 6, 7. The illustration is schematic only, in particular the corners of the passage openings 11, are each illustrated in such a way that the corners of the respective polygon are given without the radii required in practice with regard to acceptable usage times of the tools. Figure 8-a shows a regular convex pentagon as the basic shape of the passage opening 11. The bridge 41 extends approximately from the center of one side of the pentagon to the tip located opposite to this center and in its course from the side to the tip reduces its width by about 15%. The broken lines 40 with long bars indicate a virtual continuation of the edge of the passage opening 11, thus the shape the passage opening would show without the supporting bridge 41. The pentagon comprises a total of five diagonal lines 45, which are all intersected by the supporting bridge.

[0068] Figure 8-b differs from Figure 8-a in that the passage opening 11, which is covered by the screen layer 4 on its bottom side, shows a convex hexagon as its base shape. Again, the edges of the passage opening, which are covered by the bridge, are indicated by broken lines 40. The bridge 41 here again shows no constant width over its entire length. Rather, it enlarges towards its ends, so that a generously rounded transition towards the lateral edges of the passage opening results. Again, the supporting bridge is located in the center, so that it intersects with all diagonal lines.

[0069] In Figures 8-a and 8-b, the connection points 46, 46' of the bridge 41, which are closest to each other, on their opposite edges are distanced to each other by more than 120° relative to a circle around the center point of the pentagon or hexagon, respectively. The two center lines 49, 49', respectively, of the transition of the respective bridge towards the virtual lateral edges of the passage opening are distanced to each other by essentially 180° relative to a circle around the center point of the pentagon or hexagon, respectively.