PATENT DOCUMENT

Abstract:
A subassembly and a method of producing a subassembly. The subassembly has a dividing body or separating body and at least one flow channel formed on the dividing body and extending along it with at least one flow path to influence a flow of a magneto-rheological fluid along the flow channel of the dividing body. The dividing body includes a magnetic field generation device for generating a magnetic field and a field closing device. At least the magnetic field generation device and the field closing device are filled with at least one solidifying medium using a placeholder which can be removed to form the three-dimensionally predefined flow channels on the dividing body.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of copending application Ser. No. 14/413,836, filed Jan. 9, 2015, which was a §371 national stage of international application PCT/EP2013/002002, filed Jul. 8, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2012 013 480.0, filed Jul. 9, 2012; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a subassembly and to a method for producing a subassembly, wherein the subassembly comprises a divider with a flow passage extending thereon. The flow of a magnetorheological fluid along the flow passage is influenced by a magnetic field generating device in order to produce defined conditions. 
         [0003]    The prior art has disclosed subassemblies in which the flow of a magnetorheological fluid is selectively attenuated or even prevented by adjustment of a corresponding magnetic field on the flow passage. 
         [0004]    For example, dampers have been disclosed which comprise a damper piston with a magnetorheological valve, wherein the degree of damping depends on the magnetic field applied. A damping piston of this kind with a magnetorheological valve comprises a multiplicity of parts, which have to be produced carefully in order to be able to make available reproducible assembly and thus dampers without excessive series variability and hence differences in performance. 
         [0005]    An electrically operated magnetorheological damping valve comprises an electric coil wound onto a core, a damping gap, through which the magnetorheological fluid passes, and a magnetic conductor, which closes the magnetic field. The individual components must be carefully assembled and sealed off from one another in order to ensure the desired operation, sometimes at pressures of up to 600 bar. This requires considerable effort, and therefore manufacture of such subassemblies is complex and thus relatively expensive. 
         [0006]    US 2002/0130001 A1 has disclosed a magnetorheological fluid damper in which a piston has over its circumference an annular gap divided into four channel segments. The piston has an outer flow ring and an inner piston core, around the longitudinal axis of which a magnetic coil is wound. Four cross-shaped fastening grooves, which are provided with inward-leading through holes, are introduced into the outer surface of the flow ring in a manner distributed over the circumference. To connect the flow ring to the piston core, plastic is injected from the outside at the fastening grooves, passing through the through holes and the annular gap and forming sprues with radial projections which extend as far as the magnetic coil on the piston core. Here, the quantity injected is chosen so that a significant portion of the annular gap remains free for the flow of the magnetorheological fluid. However, a fluid damper of this kind has the disadvantage that the radial projections of the sprues have to bear very high shear forces when subjected to loading, and this can lead to problems with durability. Moreover, although using the injected quantity of plastic is supposed to ensure that a significant portion of the annular gap is left free, it is not possible to ensure a constant and reproducible shape of the annular gap that remains free since the liquid plastic flows into the annular gap differently on each occasion, and therefore considerable series variability is to be expected in manufacture. 
         [0007]    U.S. Pat. No. 7,849,983 B2 has disclosed a magnetorheological fluid damper which has a piston with poles at the axial ends and a coil wound around the longitudinal axis of the piston. The piston runs within a cylindrical housing and divides a first magnetorheological damper chamber from a second magnetorheological damper chamber. The damping gap is provided radially between the outer surface of the piston and the radially inner surface of the cylindrical housing. During manufacture, the piston with the metallic poles and the electric coil is introduced into a casting mold, and a polymer is injected under pressure. The piston with the polymer on the outer surface thus provides a defined outer surface. However, the disadvantage of this is that the piston has to be guided with extreme accuracy in the cylindrical housing by means of a bearing arrangement in order to avoid a nonuniform gap around the circumference and to avoid contact between the piston and the inner surface of the cylindrical housing. Moreover, the cylindrical housing must be formed from a magnetically conductive material in order to be able to close the magnetic field. 
         [0008]    It is therefore the object of the present invention to make available a method for producing a subassembly and to make available a subassembly of this kind, thus allowing reproducible production of such subassemblies at low cost. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    This object is achieved by a method having the features as claimed. The subassembly according to the invention is the subject matter of a further claim. Preferred developments are the subject matter of the dependent claims. Further advantages and features of the present invention will emerge from the general description and from the description of the illustrative embodiments. 
         [0010]    The method according to the invention is used to produce a subassembly having a divider and at least one flow passage arranged thereon or provided therein and extending along or in the divider and having at least one flow path in order to influence a flow of a magnetorheological fluid along the flow passage or a subsection of the flow passage of the divider. In this case, the divider furthermore has a plurality of components, including at least one magnetic field generating device for generating a magnetic field and at least one field closing device. The magnetic field generating device and the field closing device are filled with at least one solidifying medium, while using at least one placeholder, to form the or at least part of the flow passage, in order to form on the divider at least one three dimensionally predefined flow passage, which is available after the removal of the placeholder. 
         [0011]    The space maintained by the placeholder during filling is available as a three dimensionally predefined flow passage after the removal of the placeholder. 
         [0012]    Particularly for the hydraulically leaktight connection of the components of the divider, at least the magnetic field generating device with the field closing device of the divider is encapsulated with a solidifying medium in the form of, for example, an encapsulating compound, or is overmolded with at least one injected plastic. The method according to the invention has many advantages since it allows simple production of a subassembly according to the invention. A subassembly produced by a method according to the invention has a high reproducibility and can be subjected to high loads. The method is very cost-effective for the quality achieved. 
         [0013]    In the sense according to the present invention, the phrase stating that a flow passage extends “along” the divider is taken to mean that the flow passage extends from one end to the other end. The flow passage can be of linear design, but it can also have turns or extend in coils or obliquely from one end to the other end. 
         [0014]    The flow of the magnetorheological fluid is influenced at least by means of a subsection of the flow passage. It is not necessary to exert an influence over the entire length. 
         [0015]    The core is preferably surrounded by a coil holder, which is composed of plastic, for example. An electric coil device is preferably wound onto the coil holder. 
         [0016]    The connection formed by the solidifying medium is preferably hydraulically pressuretight, forcing the magnetorheological fluid to flow via the flow passage. 
         [0017]    It is advantageous if the magnetic field generating device is wound onto the core or the coil holder first, before filling. The core can be introduced into the magnetic field generating device before filling. At least one placeholder is positioned in the field closing device. The core with the magnetic field generating device and the field closing device is then filled, ensuring that, after the subsequent removal of the placeholder or placeholders, the at least one flow passage is available, while the divider per se is hydraulically leaktight. 
         [0018]    It is advantageous if at least one dividing wall is arranged on the coil holder in order to divide the flow passage into two or more flow paths. 
         [0019]    For production, an insert or an inserted part or a push-in part is formed, being formed, for example, from a stack comprising a first dividing template as a placeholder, at least one dividing wall and at least one second dividing template as a placeholder. 
         [0020]    It is also possible here for an insert to be formed from one or more placeholders. An individual placeholder or a placeholder made up of one or more parts is used, for example, if a flow passage is not divided into partial passages. If, on the other hand, the flow passage is to be divided into a plurality of flow paths, the insert comprises a stack of different components, which are stacked one on top of the other. 
         [0021]    During assembly, the core is preferably introduced with the coil holder and the electric coil device and at least one insert into the field closing device. The field closing device is preferably introduced into a mold before or afterward. Encapsulation with the solidifying medium in the form, for example, of an encapsulating compound is then carried out, or plastic or other materials advantageous for this purpose is/are injected. Encapsulation can take place at normal pressure, but can also take place using reduced pressure and/or excess pressure. 
         [0022]    In all the embodiments, the solidifying medium is preferably cured after the casting operation. Curing can be assisted by temperature adjustment. The use of UV radiation or some other radiation, for example, is also possible in order to accelerate the solidification process. The use of chemical agents is also possible. 
         [0023]    Analogously, some other suitable method, such as injection molding (of plastics) can be used instead of encapsulation. 
         [0024]    The embodiments illustrated show the use of a structure according to the invention in a damper, e.g. as a shock damper in a vehicle, bicycle or prosthesis. Analogously, the structure can be used without a movable piston and piston rod as a valve. 
         [0025]    In all embodiments, at least one placeholder is removed after the curing process in order to free the flow passage and/or the flow paths of the flow passage. 
         [0026]    In particular, a subassembly according to the invention is produced by one of the methods described above. The subassembly according to the invention has a divider and at least one flow passage provided thereon and extending through the divider or along the divider and having at least one flow path in order to influence a flow of a magnetorheological fluid along the flow passage—or in subsections thereof—of the divider. The divider comprises at least one magnetic field generating device for generating a magnetic field and one field closing device. The field closing device with the magnetic field generating device is filled with a solidifying medium, while using at least one placeholder, such that the divider has at least one three dimensionally predefined flow passage. After the removal of the placeholder, the flow passage is available. 
         [0027]    The subassembly according to the invention has many advantages since it can be produced easily and reproducibly and allows functionally reliable operation. 
         [0028]    The subassembly according to the invention preferably makes available a hydraulically leaktight divider which, in particular, allows flow only through the flow passage arranged thereon or through the flow connections provided thereon. In this case, the flow capacity depends, in particular, on the magnetic field of the magnetic field generating device. Without a magnetic field, a magnetorheological fluid can pass substantially unhindered through the flow passage. With a strong magnetic field, the through flow of a magnetorheological fluid can also preferably be completely prevented. 
         [0029]    The solidifying medium can be at least one encapsulating compound or contain such a compound. The solidifying medium can be cast or injected. For example, it is possible to use at least one medium which is or becomes liquid under certain conditions and is then cast or injected and then cures. The solidifying medium can be a medium which cures or can contain at least one such medium, for example. 
         [0030]    The magnetic field generating device with the field closing device of the divider is preferably filled and/or encapsulated and/or overmolded with a solidifying medium. 
         [0031]    Owing to the fact that the components of the divider are, in particular, encapsulated together and are thus firmly connected to one another by the solidifying medium, durable functioning can be reliably ensured. In the case of subassemblies from the prior art, in contrast, it is generally necessary to connect each individual component to the other components and seal them off from the other components in a complex process. Such an assembly process is complex and, at the same time, prone to error. The subassembly according to the invention, on the other hand, makes available a functionally reliable subassembly in a simple manner. At the same time, the solidifying medium ensures a firm and permanently leaktight connection between the individual components, even if these exhibit inaccuracies owing to relatively large variations in the manufacturing tolerances or indeed surface imperfections or roughness. 
         [0032]    As a solidifying medium, it is possible, for example, to use an encapsulating compound and/or a solidifying and, in particular, curing casting compound. It is possible, for example, for a two component material to be used as a solidifying medium, which is initially capable of being processed in a flexible manner and then automatically cures. Here, curing can take place under defined conditions, e.g. an increased temperature. However, it is also possible for curing to take place without special conditions, e.g. at room temperature. 
         [0033]    In particular, a hydraulically leaktight connection between the components of the divider is made possible. In particular, the solidifying medium restricts the flow of the magnetorheological fluid substantially and preferably virtually completely to the flow passages. However, it is also possible for at least one separate bypass passage to be provided. 
         [0034]    Through the use of one or, indeed, at least one placeholder, a spatially precisely defined shape of the flow passage is made possible. The placeholder can be of one-piece design. The placeholder can also consist of a plurality of individual parts. After filling, the placeholder is removed and is preferably reusable. The placeholder can consist of a dividing template or can comprise at least one such template. The dividing template can be metallic or can consist of some other suitable material. 
         [0035]    The use of a placeholder composed of a material such as wax or the use of a eutectic metal is also possible. After the filling process, the placeholder can then be washed out or melted out of the divider. Dissolving with chemical agents is also possible. 
         [0036]    The placeholder itself or the melted material can be reused. 
         [0037]    At least one flow passage is preferably divided by at least one dividing wall into at least two flow paths. Here, a flow path can also be regarded as a partial passage. The at least two flow paths are preferably divided from one another at least partially and, in particular, completely over the entire length thereof. By means of such a dividing wall, which can be embodied essentially as a thin and, preferably, ferromagnetic dividing plate, for example, without being restricted thereto, the flow passage is divided by simple means into two partial passages or flow paths. Even more effective influencing of the flow through the flow passage is thereby possible. In simple cases, a thin dividing plate is used as a dividing wall. The dividing wall is preferably thin relative to the height of a flow path of the flow passage. As a result, the full flow cross section is reduced only slightly, thereby making it possible to maintain a small overall size. In this case, the faces of the dividing wall can have contours which are advantageous in terms of flow engineering. 
         [0038]    As a particularly preferred option, the dividing wall is designed as a separate dividing plate and is encapsulated with the divider by means of the solidifying medium. Simple manufacture and a durable subassembly are thereby made possible. 
         [0039]    The dividing wall preferably has at least one latching device, which latches with the solidifying medium and/or with other components of the divider, thus making it possible to ensure reliable operation, even at high pressures. In particular, two, three or more latching devices in the form of latching teeth, latching hooks, latching eyes or latching grooves or the like, for example, are provided in order to allow a firm connection between the dividing wall and the divider. 
         [0040]    In all the embodiments, at least one flow path has a shallow cross section in the flow direction, wherein said cross section can be straight or in an arc shape. In particular, a width of the flow path is more than twice and, in particular, at least four times a height of the flow path in the direction of the field lines. In particular, the length of the flow path in the flow direction is greater than a height of the flow path transversely to the flow direction. Effective influencing of the magnetorheological particles in the magnetorheological fluid is made possible by a shallow gap as a flow path, making possible finely graduated or continuous adjustment of the flow resistance through the flow passage, right up to blocking. 
         [0041]    In all the embodiments, there is a particular preference for at least one magnetic field generating device to be designed as an electric coil device, to which at least one core composed of a ferromagnetic material is assigned. In particular, the electric coil device and the core are encapsulated with the divider by means of the solidifying medium. 
         [0042]    An electric coil device allows a flexible, quick and defined change in the effective magnetic field in a short time, thus making possible real-time control of the influencing of the flow resistance through the flow passage of the dividing device, for example. 
         [0043]    In particularly preferred embodiments, the core has at least one lateral constriction transversely to the longitudinal axis thereof. This constriction can be formed on one or more longitudinal sides and/or end faces of the core or can be designed to run completely around the core. As a result, a smaller overall volume is made possible, offering considerable advantages in the case of subassemblies where overall volume is a difficult issue. 
         [0044]    By means of the constriction, the ferromagnetic material of the core, the saturation flux density of which is generally significantly higher than the saturation flux density of the flowing fluid, is better utilized. Moreover, the mean winding length of the coil can be reduced, which can significantly improve the electrical properties thereof. 
         [0045]    It is advantageous if the core is surrounded by a coil holder, on which the electric coil device is mounted. 
         [0046]    The coil holder can be composed of a plastic, for example, and facilitates the winding of the coil. At the same time, damage to the windings at the edges of the iron core is avoided during winding or during subsequent operation. It is also possible to wind the coil directly onto the coil holder and to insert the core later. The coil holder preferably allows coaxial positioning, e.g. if the divider is designed as a piston. 
         [0047]    At least one flow path is preferably arranged between a pole cap of the core and the field closing device. Such an embodiment allows particularly effective use of the magnetic field which emerges from the pole cap, crosses the flow path and is directed back via the field closing device, thus making available an effective subassembly. 
         [0048]    In particular, at least one pole cap is rounded and is preferably designed substantially as a cylinder segment and at least substantially adjoins a flow path. 
         [0049]    In preferred embodiments, the divider is designed as a piston and, as such, is arranged movably in a piston guide. The piston is preferably connected to a piston rod. However, the piston can also be connected to piston rods on both sides—i.e. what is referred to as a continuous piston rod. At least one piston rod is preferably screwed on, in or against. 
         [0050]    In such embodiments, it is preferred if the electric coil device is aligned transversely to a longitudinal axis of the piston guide. This means that the electric coil device is not arranged parallel to the piston movement but, in particular, is arranged perpendicularly thereto. However, it is also possible for the coil device to be embodied parallel to the piston movement (coaxial coil). 
         [0051]    An axis of the electric coil device is preferably aligned transversely to a longitudinal axis of the piston guide. The field closing device preferably forms a piston main body. The piston main body is composed of a ferromagnetic material, such as a ferrous material, for example. 
         [0052]    In such embodiments, the field closing device preferably surrounds the electric coil device in a circumferential direction of the piston. In the case of a horizontal arrangement of the electric coil device, when the electric coil device is arranged transversely to the longitudinal axis of the piston, it is thereby possible for the field closing device to effectively close the field, thus allowing a simple and effective structure. 
         [0053]    In all the embodiments, it is particularly preferred if the piston main body has at least one undercut, grooves, slots, irregularities, a very rough surface or the like, which are filled at least partially with the solidifying medium or the encapsulating or injection compound. By means of such an embodiment, a particularly firm connection is ensured within the divider, thus ensuring that the subassembly is sufficiently stable, even at high and very high differential pressures on both sides of the divider of 100, 200, 400 or even 600 bar. 
         [0054]    Further advantages and properties of the present invention will emerge from the description of the illustrative embodiments, which are explained below with reference to the attached figures. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0055]      FIG. 1  shows a schematic cross section through a subassembly according to the invention, which is embodied as a damper; 
           [0056]      FIG. 2  shows a schematic cross section through a subassembly  1 ; 
           [0057]      FIG. 3  shows a cross section through the subassembly according to  FIG. 2 , at right angles to the illustration according to  FIG. 2 ; 
           [0058]      FIG. 4  shows a piston for a subassembly according to the invention; 
           [0059]      FIG. 5  shows a core for the subassembly according to  FIG. 2 ; 
           [0060]      FIG. 6  shows a dividing wall for the subassembly according to  FIG. 2 ; 
           [0061]      FIG. 7  shows the core with a coil holder and dividing walls for the subassembly according to  FIG. 2 ; 
           [0062]      FIG. 8  shows a perspective illustration of the subassembly  1  without a field closing device; 
           [0063]      FIG. 9  shows a perspective illustration of the subassembly  1  without the field closing device; 
           [0064]      FIG. 10  shows a schematic illustration of a stack; 
           [0065]      FIG. 11  shows a highly schematized cross-sectional illustration of another subassembly; 
           [0066]      FIG. 12  shows a highly schematized front view of another subassembly; and 
           [0067]      FIG. 13  shows a cross-sectional illustration of the subassembly according to  FIG. 12 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0068]    In  FIG. 1 , a damper  50  according to the invention is depicted in a highly schematized cross section. The damper  50  has a housing  43 , in which the subassembly  1  acts as a piston  30 . Connected to the piston  30  is a piston rod  32 , which extends outward out of the housing  43 . 
         [0069]    It is likewise possible for a valve according to the invention to be made available. The invention is not restricted to the structure of a damper but can also be directed to a valve. In this case, such a valve can be inserted in a damper, for example, although this is not the only possibility. As a valve for a damper, it can be inserted in the piston or take the form of an external valve, for example. 
         [0070]    In the damper  50  in  FIG. 1 , a compensating space  42 , which is separated from the remaining volume of the damper  50  by a dividing piston  41 , is provided to compensate for the volume of the piston rod  32 . It is also possible to use a respective piston rod on each face of the piston, thereby allowing the compensating space and the dividing piston to be eliminated. The seal  51  serves as a sealing means (sliding seal) between the moving piston  35  and the housing  43 . The seal  51  can also be a permanent magnet seal. 
         [0071]    The subassembly  1  serving as a piston  30  serves as a divider  2  and has a magnetic field generating device  8 , which is here designed as an electric coil device  19 . 
         [0072]    In the section according to  FIG. 1 , the core  20  can be seen, which is surrounded by a coil holder  23  made of plastic. The electric coil device is wound around the coil holder  23 . 
         [0073]    The piston  30  comprises the piston main body  35 , which simultaneously serves as a field closing device  9  and is here designed as a ring-shaped conductor. In the illustration according to  FIG. 1 , the flow passages  3  and  4  can be seen, which are each divided here into two respective flow paths  5  and  6  by dividing walls  11 . 
         [0074]      FIG. 2  shows, in a somewhat enlarged view, a subassembly  1 , which is here likewise embodied as a piston  30 . The piston  30  is connected to a piston rod  32 . The piston main body  35  and the core  20  and the coil holder  23  each form components  7 , which are here connected to one another within the divider  2  by the solidifying medium  10  in the form, for example, of an encapsulating compound  10  or of a plastic. Flow through the piston  30  can take place in the flow direction  15  through the flow passages  3  and  4 . 
         [0075]      FIG. 3  shows the subassembly  1  according to  FIG. 2  in a section which is arranged at right angles to the section according to  FIG. 2 . Here, the core  20  is depicted along the longitudinal extent  26  thereof. The core  20  is surrounded by the coil device  19 , the individual windings of which here extend substantially parallel to the plane of the paper. Provided in the piston main body  35  is an undercut  45  or a groove, which has filled with the solidifying medium  10  during the encapsulation or injection process. After curing, the undercut  45  forms an effective safeguard (positive engagement), reliably preventing the electric coil devices  19  from being pulled or pushed out of the piston main body  35 , even at high pressures. 
         [0076]    In addition,  FIG. 3  also shows a mold  40 , into which the subassembly  1  is inserted during assembly, before the solidifying medium is added in order to ensure a hydraulically leaktight connection within the divider  2 . The mold  40  has a form matched to the envisaged external shape of the subassembly  1 . By means of the external shape, the piston and, especially, the approach-flow region of the flow passages  3 ,  4  can be optimized in terms of flow engineering, and, in this case, the solidifying medium  10  in the form of the encapsulating compound, for example, can cover virtually the entire end-face area of the piston main body  35 . 
         [0077]    Additional molds can be used analogously to mold  40 , e.g. in order to configure the opposite area. The flow passages formed by the piston main body in  FIG. 3  and the fastening of the piston rod, in particular, can also be accomplished by a correspondingly shaped solidifying medium. 
         [0078]      FIG. 4  shows a piston main body  35  for the subassembly  1  according to  FIG. 2  or  FIG. 1 . Here, the piston main body  35  serves as a field closing device and carries the magnetic field back again after passage through the flow passage. The flow passages  3  and  4  are clearly visible here. The flow passages  3  and  4  each have a shallow cross section  39 . Assembly holes  44  are furthermore provided, being used, for example, for handling with a matching tool. The inflow and outflow contours of the flow passages  3  and  4  can be embodied in an advantageous way in terms of flow engineering by rounding the edges, profiling etc. 
         [0079]    An embodiment which is preferred in the case of cost sensitive applications, in which the ferromagnetic piston main body  35  is dispensed with or can be composed of plastic or a comparable material, is not shown. In this case, the piston main body can be produced in the working step in which the coil is encapsulated or overmolded and the dividing walls are fixed. It is particularly advantageous to encapsulate or overmold the piston rod in the same operation. 
         [0080]    With such a structure, the magnetic circuit can be closed by means of the housing  43 . If the dividing walls or flow passages are situated radially on the very outside of the piston, there is no plastic or no encapsulating compound in the magnetic circuit. 
         [0081]    It is also possible, in addition to the flow passage  3  (and  4 ) situated in the magnetic field, to produce at least one flow passage not situated in the magnetic field, e.g. in the form of a simple hole, by means of the methods described above (bypass passage). One possible position would be between the passages  3  and  4  viewed in relation to the end face, as an extension of the assembly hole  44 , giving rise to a bypass passage. By way of example, this can be accomplished by means of a placeholder  29  in the form of a simple wire, which is removed after the encapsulation process. This wire can be between 0.1 mm and 10 mm thick, for example. The placeholder  29  can also be encased, wherein the outer circumferential surface bonds to the encapsulating compound, and the placeholder (wire) can be pulled out. It is thereby possible to dispense with a release agent for easier removal, and this facilitates the process. The inner circumferential surface can preferably be provided with an antifriction layer, thereby facilitating removal. 
         [0082]      FIG. 5  shows the core of the subassembly  1  from  FIG. 2 , illustrated separately and an enlarged scale. The pole caps  24  and  25  are rounded and are here matched to the radius of the piston  30  or to the internal radius of the flow passages  3  and  4 . Pole cap  24  adjoins the damping passage  3  and, in particular, the flow path  6  of flow passage  3 . Here, pole cap  25  directly adjoins the flow path  6  of flow passage  4 . It is also possible for the pole caps  24  and  25  to be coated with a thin layer, for example, with the result that there is a small spacing between the actual pole caps  24  and  25  and the flow passages  3  and  4  respectively. 
         [0083]    The core  20  can also be produced from a plurality of parts, wherein these core parts can have different magnetic properties. In this case, regions of the core can be hard-magnetic and other regions can be magnetically nonconductive (not ferromagnetic. The multi-part structure of the core also makes it possible to insert the core into the coil holder  23  only after the winding of the coil. 
         [0084]      FIG. 6  shows a dividing wall  11  embodied as a dividing plate  12 , which here has latching devices  13  in the form of latching teeth  14 . By means of the latching devices  13  or latching teeth  14 , the dividing wall  11  interlocks with the solidifying medium during encapsulation, ensuring that the dividing wall  11  is accommodated in the subassembly  1  reliably and in a defined and spatially fixed manner. 
         [0085]    At least one film, adhesive tape, layer or coating which forms the placeholder during the encapsulation process and is then chemically dissolved, etched away or melted out can be applied to the dividing plate  12  in the central area and preferably on both sides. The flow passage is thereby formed. The placeholder can also be composed of a eutectic metal, which is melted and removed again after the encapsulation process. 
         [0086]      FIG. 7  shows the core  20 , which is surrounded by a coil holder  23  and on which two dividing plates  12  are additionally placed. A flow path  6  of the flow passages  3  and  4  can be seen between each of the pole caps  24  and  25  and the dividing plates  12 . Latching means  34 , which are used to receive the dividing walls  11  in a defined manner, are provided on the coil holder  23 . 
         [0087]    Transversely to its longitudinal axis  21 , the core  20  here has constrictions  22 , thus saving overall volume in the axial direction of the piston  30 . Owing to the constrictions  22 , the coil  19  expands less far in the axial direction, thus allowing an axially shorter subassembly  1 . 
         [0088]    Here, the flow passages  3  and  4  have a length  18  in flow direction  15  which is considerably greater than a height  17  in the direction of the longitudinal axis  21  of the core  20 . Here, the width  16  of the flow paths  5  and  6  of the flow passages  3  and  4  extends along a curved line and is likewise considerably greater than the height  17  of the individual flow paths  5  and  6 . 
         [0089]    Typical values for the length  18  of the flow passages  3  and  4  are between about 10 and 60 mm. The width  16  is generally between about 5 mm and 20 mm, and preferred passage heights  17  are between about 0.2 and 2 mm. 
         [0090]    In this case, a plurality of flow paths can be provided. For example, five, six, eight, nine or ten flow paths can be associated with one flow passage. It is also possible for three, four or more flow passages to be provided. Typically, the wall thickness of the dividing walls  11  is between 0.1 mm and 1 mm. 
         [0091]    The free flow cross section as the sum of all the flow passages is dependent on the shape of the passages, the fluid used, the piston area and the desired force range. Typical flow cross sections are in a range between about 10 mm 2  and about 200 mm 2 . Mean flow velocities of up to 30 m/s or even 60 m/s or above are possible. Of course, the volume flow depends on the dimensions and, in some examples, can reach and exceed 100 ml per second. Indeed, values of 200 ml per second or 300 ml per second and even more are also possible. The electric coil device  19  can be composed of different materials. For example, it can be formed from copper or even from anodized aluminum or the like. It is also possible for a plurality of coil devices  19  to be provided. 
         [0092]    The dividing plate  12  can also be embodied as a planar plate, and this, together with a core  20  with planar pole caps  24 , gives a planar flow passage situated therebetween. 
         [0093]    A subassembly  1  without the piston main body  35  is depicted in perspective view in  FIG. 8 . The cables  38 , which lead to the electric coil device  19  in the interior, and the dividing plates  12 , which divide each of the flow passages  3  and  4  into two flow paths  5  and  6 , respectively, are clearly visible. The latching means  34  for the axial fixing of the dividing walls  11  or dividing plates  12  are visible and, in the fully assembled state, rest against the inside of the piston main body  35 .  FIG. 8  and also  FIG. 9  show the state after encapsulation with the solidifying medium, although the piston main body  35  has been omitted in the illustrations for greater clarity in each case. 
         [0094]    The offset  46 , which consists of the solidifying medium  10  and, in this case, of the encapsulating compound or of an injected plastic  10  and fills the undercut  45  in the piston main body  35 , is also clearly visible. 
         [0095]    In  FIG. 9 , the placeholders  29  in the form of dividing templates  36  and  37  are still inserted in the subassembly  1 . After curing, the dividing templates  36  and  37  can be removed, leaving the flow channels  3  and  4  or flow paths  5  and  6  with precisely defined dimensions. For this purpose, the dividing templates  36  and  37  are pulled out in an axial direction. The dividing templates can also be part of the mold  40  shown in  FIG. 3 . The dividing templates are also pulled out in an axial direction along with or after the removal of the mold  40 . 
         [0096]    The dividing templates  36  and  37 , which can thus be reused, can be brought precisely to the desired dimensions by means of a grinding operation or the like, for example, allowing highly accurate subassemblies  1  to be manufactured in a reproducible manner. 
         [0097]    It is also possible to chemically dissolve or melt the placeholders  29  or dividing templates  36  and  37 , for example. In that case, new dividing templates  36  and  37  are required for each subassembly. However, the melted material can be reused directly or after cleaning or filtering. 
         [0098]    It is also possible to surround the placeholder  29  or dividing templates  36  and  37  with a movable shell/sleeve, wherein the outer circumferential surface bonds to the encapsulating compound and the placeholder  29  can be pulled out.  FIG. 10  shows a stack  28  as a placeholder  29 , which serves as an insert in a subassembly  1 . For this purpose, the dividing template  36  or  37  is first of all laid down, and the dividing wall  11  is then applied before the second dividing template  37  or  36  is laid down. Together with the core  20 , which is surrounded by the coil holder  23  and the coil  19 , the insert  27  is introduced into the piston main body  35 . Both are introduced into the mold  40  before the cavities are filled with solidifying medium  10 . In order to avoid air inclusions, it is possible to operate under a vacuum and/or under excess pressure. 
         [0099]    Instead of the stack  28  described above, consisting of a dividing wall  11  and respective dividing templates  36  and  37 , it is also possible to install in the same overall volume a stack consisting of, for example, two thinner dividing walls combined with three thinner dividing plates. The dimensions and shapes of the core  20 , of the piston main housing  35  and of the coil holder  23  together with the coil  19  do not have to be altered for this purpose since the solidifying medium compensates for the differences and fixes all the components as it solidifies. It is thus possible to produce different flow passage designs (variants) without major effort. 
         [0100]    A stack can contain any number of dividing walls  11 , it being possible for typical stacks to contain one to ten or twenty or more dividing walls. For assembly, the number of dividing walls+a placeholder  29  is generally used. 
         [0101]      FIG. 11  shows a highly schematized cross-sectional illustration of another subassembly  1  according to the invention, which comprises a divider  2 . The divider  2  has a field closing device  9 , a flow passage  3  in the divider  2 , a core  20  and an electric coil as a field generating device  8 . The divider  2  is filled by means of a solidifying medium  10 . Before filling, an insert  27  has been introduced as a placeholder  29 . The placeholder  29  ensures the formation of a spatially defined and reproducible flow passage  3  in the divider  2 . The placeholder can be designed as a dividing template or can be composed of a material which can be washed out, melted or dissolved, which is removed again after solidification or curing. Consequently, the placeholder can be composed of metal or, alternatively, can be manufactured from wax, for example. 
         [0102]    To ensure a pressuretight connection (leaktightness . . . ) between the component  7  and the field closing device  9  in the regions which are not fully encapsulated (e.g. relative to the flow passage), the core  20  has in these regions at least one recess which is filled with encapsulating compound or the medium  10  during the encapsulation process. 
         [0103]      FIG. 12  shows a highly schematized front view of another subassembly  1 , which, as in the example shown in  FIG. 11 , comprises a flow passage  3  with just a single flow path. Here, the flow passage  3  is not subdivided.  FIG. 13  shows a cross-sectional illustration of the subassembly  1  shown in  FIG. 12 . Once again, the divider  2  has a field closing device  9 , a flow passage  3  in the divider  2 , a core  20  and an electric coil as a field generating device  8 . 
         [0104]    A space must remain free between the magnetic field generating device  8  and the inner end face of the field closing device  9 . This is achieved by inserting a placeholder  29  made of wax, for example. After encapsulation, this is removed by melting. It is also possible to use other materials customary for encapsulation processes instead of wax. The placeholder  29  can also be shaped in such a way that it shapes the flow passage in a corresponding way. The space to be kept free or in a multiplicity thereof can be at any desired position of the subassembly. 
         [0105]    It is also possible to use other meltable media, thermoplastics etc. as placeholders  29  in order to enable the placeholder  29  to be removed again by melting after filling. 
         [0106]    Here, a collecting space  48  is provided at one end of the divider  2 , said space being connected to the adjacent chamber by a plurality, in this case three, openings  49 . It is also possible for two different placeholders  29  to be inserted, namely, for example, a dividing template  36  for the formation of the flow passage  3  and another placeholder to form the collecting space  48 . 
         [0107]    The field closing device  9  can be provided at one or both ends with threads, on which a piston rod, for example, is secured. 
         [0108]    Through the defined method of working and the defined dimensions of the dividing walls and of the dividing templates it is possible to produce highly accurate subassemblies at low cost and in a simple manner in relatively large numbers. By virtue of the accurate tolerances, it is also possible to divide a flow passage into many flow paths, which are divided from one another by the dividing walls as partitions. Since all the individual parts are manufactured with high accuracy, the cumulative tolerance is low. That is very advantageous since considerable loads can act on the individual flow paths or flow passages if the dimensions of the individual flow passages or flow paths are different, and these can lead to bending of dividing walls  11  or dividing plates  12 . 
         [0109]    In all cases, the dividing walls can be embodied as bent partitions in a round piston. The piston rod can be screwed or adhesively bonded. 
         [0110]    If a large number of dividing walls  11  are stacked as partitions, the individual tolerances accumulate to give a larger cumulative tolerance, which can be disadvantageous in the case of the series-produced part. In that case, the performance of individual actuators can differ widely. To manufacture the individual parts with high accuracy, so that the cumulative tolerance is low, is complex and expensive in series production. The invention makes available an advantageous subassembly  1  and an advantageous method for production. It is thus possible to make available a subassembly with lower overall tolerances with mass-produced individual parts having, in some circumstances, even greater tolerances (=cheaper). 
         [0111]    In particular, it is also possible for all components to be hydraulically leaktight, even in the case of high pressures/forces. 
         [0112]    The subassembly can respond adaptively through magnetic field changes, resulting as it were in a change in viscosity of the liquid. The control of high pressures is a significant advantage of the partitioned structure (in the case of a small overall volume, especially of short length). 
         [0113]    The dividing walls  11 —also referred to as partitions—are often embodied so as to be thin and, in preferred embodiments, have thicknesses  47  between about 0.3 mm and 0.7 mm. It is thereby possible to save overall volume and overall height. The height  17  of the flow paths  5 ,  6  is, in particular, between 0.2 mm and 2 mm. In the case of certain structures, e.g. energy absorbers for steering systems, a multiplicity and, specifically, fourteen dividing walls  11  as partitions, for example, can be stacked one on top of the other. With two such packs, it is possible to make available a total of 30 passages or more, which are subjected to pressures of up to 600 bar or high surface loads of 60 N/mm 2  or above resulting therefrom. 
         [0114]    However, if the flow paths  5 ,  6  each have very different spacings, this results in a different magnetic field strength when a magnetic field is applied: the magnetic field in the higher flow path is lower than in the gap which is not so high or in the lower flow path. The different magnetic field influences the magnetorheological fluid differently, and a lower pressure is established in the higher flow path, and a higher pressure is established in the lower flow path. This can lead to considerable transverse loads on the dividing walls  11 , which may bend and even be destroyed. 
         [0115]    However, irrespective of this, even if the magnetic field is absolutely the same, the height of the gap or of the flow path in the direction of the field lines is decisive since a lower height leads to a higher possible counterpressure. Different heights of different flow paths lead to different counterpressures and, as a result, to pressure differences. 
         [0116]    The pressure differences between individual dividing walls  11  lead to force differences on the dividing walls  11 , which can lead to deformations of the thin partitions  12 . Particularly at high pressures, such a deformation can cause material overloading and deficient functioning of the actuator. This can even be to the extent that two dividing plates  12  touch owing to the deformation, leading to a magnetic short circuit and hence to an almost complete pressure drop in one flow passage or in one flow path. Unforeseen leaks in individual passages (leakage) may cause similar loads or disadvantages. 
         [0117]    Through uniform approach flow, the invention enables bending of the dividing plates  12  to be avoided. 
         [0118]    One advantage of encapsulation-induced or adhesive bonding of the electric coil device  19  to the dividing walls  11  is that the dividing walls  12  are also fixed during the encapsulation process. 
         [0119]    The toothing in the lateral outer region of the dividing walls  11  allows positive engagement in the divider  2 . The constriction of the iron core  20  allows a saving the of overall volume, this being important for the stroke length and overall length. 
         [0120]    The undercut  45  in the piston  30  serves for positive engagement of the assembly comprising the electric coil device  19 , the core  20  and the coil holder with the piston  30 . The undercut  45  can also be embodied as a round or angular notch or as toothing. The undercut also ensures leaktightness. 
         [0121]    Here, bent dividing walls  11  offer better energy efficiency. Straight dividing walls have advantages in terms of production costs. 
         [0122]    The coil holder  23  holds the dividing walls  11  in the axial direction before encapsulation. The dividing walls  11  are held in the radial direction by means of the dividing templates  36  and  37  before encapsulation. 
         [0123]    During the production process, the parts which cannot be removed from the mold are first of all cleaned. The parts which can be removed from the mold are greased or oiled. A special release agent can also be used. 
         [0124]    The cable  38  is then soldered on or connected to the coil  19 . The piston  30  is screwed and/or adhesively bonded to the piston rod  32 . 
         [0125]    A sandwich of the coil  19 , dividing templates  36  and  37  and dividing walls  11  is assembled with the inserted part  27  or stack  28 . All tolerances are compensated for by the thickness, especially the defined thickness, of the dividing walls  11  of the partition plate. 
         [0126]    The sandwich is pushed into the piston  30 . If an encapsulating compound or a plastic is used as the solidifying medium, this may be heated up. If a vacuum unit is used, the piston is positioned in an appropriate manner, the vacuum bell is closed and the vacuum pump is switched on. Owing to the vacuum, the air is sucked out of the piston  30 , and the solidifying medium  10  flows into the piston, ensuring that as few air inclusions as possible occur. Air inclusions can have a bad effect on leaktightness and on the fixing of the components. 
         [0127]    After curing, release from the mold can take place, with the dividing templates  36  and  37  being pulled out of the piston. The dividing templates  36  and  37  can also be part of the mold  40  or can be connected detachably to the mold and removed jointly during mold release. 
         [0128]    Finally, the remaining solidifying medium or encapsulating compound  10  is cleaned off the flow passages  3 ,  4 , if necessary. 
         [0129]    The latching devices  13  on the dividing walls  11  can be round, triangular or polygonal, for example. Barbs can be provided. The teeth can also be bent and turned downward, for example. 
         [0130]    The dividing walls  11  are preferably composed of a magnetically conductive (ferromagnetic) material. The wall thickness is preferably constant but can also differ. The thickness of the dividing wall can also vary (e.g. conically) over the width  16 , as seen transversely to the flow direction or in the flow direction. The dividing walls can also have any other shapes, e.g. corrugated. It is also possible for two or more dividing walls with different configurations, shape or material to be arranged one behind the other. It is also possible to leave a gap between the dividing walls arranged one behind the other, as seen in the flow direction, before encapsulation, said gap subsequently being filled by the solidifying medium. It is also possible to integrate a sensor, e.g. a magnetic field strength or temperature sensor, into said gap and then to encapsulate or overmold it. 
         [0131]    In the case of high pressure actuators, high forces may arise in the flow direction due to the end face and the dissipation of the shear stresses of the magnetorheological fluid (MRF). Overlapping encapsulation enables this to be dissipated efficiently and acts like an extensive adhesive bond. 
         [0132]    The surface of the dividing walls  11  can be smooth, but is preferably rough or roughened, at least locally. This gives a better bond with the solidifying medium. 
         [0133]    The core composed of a ferromagnetic material can be constricted at the end faces and/or laterally, thus allowing more windings for the same overall volume. It is also possible for the core to be composed of hard magnetic material, e.g. AlNlCo, or a permanent magnet can also be integrated into the core in order to produce a defined magnetic field without a current so as to achieve a defined basic force. 
         [0134]    Since the dividing templates  36  and  37  as placeholders  29  can preferably be used several times, they can be produced with high accuracy, e.g. by grinding. In this way, the higher production costs of the dividing templates are spread over a large number of components. 
         [0135]    In order virtually to eliminate manufacturing tolerances, the precision dividing templates are combined with dividing walls of the correct thickness and then installed. 
         [0136]    The placeholders  29  or  36 ,  37  can also be manufactured with an undersize and shaped in such a way that they distribute the height tolerance as uniformly as possible between all the flow channels through thickness tolerances of the dividing walls  11 . The inclusions of solidifying medium or of the encapsulating compound which may occur in the flow passages here are generally very thin walled and can subsequently be removed. 
         [0137]    The cable  38  is preferably encapsulated in the piston rod  32  at the same time. In addition to cable  38 , it is also possible for further cables, e.g. for temperature sensors etc., to be encapsulated at the same time. It is then no longer necessary to seal the piston rod  32 . It is also possible to integrate an anti-twist safeguard for the piston rod. The piston rod can be shaped in the connection region in such a way that a positive connection to the piston is obtained through overlaps with the solidifying medium. 
         [0138]    As an alternative, the cable  38  can also be additionally sealed ( 0 -rings; special screwed joint etc.). For this purpose, soldering pins or finished plug-in parts can be molded in or cast in directly on the coil and/or the piston. 
         [0139]    In order to ensure leaktightness between the inserted part after overmolding with injected plastic or the encapsulating compound  10 , they can be coated with hot melt adhesive or the like. It is thereby possible to compensate for stresses which arise between the various components, especially in the event of temperature changes. 
         [0140]    The wire used for the electric coils  19  can be provided with a shrink-on sleeve, which is coated internally, externally or internally and externally with hot melt adhesive. 
         [0141]    Use is preferably made of the arrangement visible in  FIG. 2  having a “horizontal” electric coil device  19 , in which the coil holder  23 , the core  20  and the dividing walls  11  are encapsulated. For this purpose, a corresponding mold  40  and, in particular, a negative mold, is preferably used. This unit can then be inserted into the remainder of the magnetic field circuit, e.g. a piston  30  or a valve. After this, a firm and leakedtight connection is produced, which is stable at least up to certain axial forces. The connection can be accomplished by adhesive bonding, ultrasonic welding, hot melt adhesive or a thread. 
         [0142]    It is also possible to produce the connection by means of an injection process. For this purpose, it is also possible for the solidifying medium or the encapsulating compound to be injected. “Encapsulation” is also intended to include injection. Preferably, overmolding is performed with plastic. 
         [0143]    In one variant, the coil device  19  can be ready-overmolded and, in this case, preferably forms “partition holders” projecting slightly outward. Together with the dividing wall  11  (partition), the coil device  19  is pushed into the piston  30 , as a result of which the partition holders are pressed inward and firmly clamp the dividing wall  11 . 
         [0144]    In another variant, it is possible to use partition holders which are similar to those above but are part of the coil holder. The core, the coil holder with the coil device  19  and the dividing walls  11  are pushed into the piston, during which process the projecting tabs of the partition holder bend and are pressed against the dividing wall  11 . By this means, the dividing wall  11  is held in position and the flow passage is sealed off from the coil device  19 , simplifying encapsulation. 
         [0145]    Also possible is ultrasonic welding, during which the unit influencing the flow passage is produced. A dividing wall  11  can be incorporated or welded in subsequently by means of ultrasonic welding. In this case, the dividing wall  11  can be encased in the solidifying medium or in the encapsulating compound at the faces or radially from the outside inward (in the direction of the core center). 
         [0146]    An alternative production method envisages encapsulating or overmolding the core together with the coil holder and coil with plastic in a mold in such a way that the regions of the flow passages and dividing walls remain free. This part is secured in the piston main body in a further work step, together with the dividing walls. 
         [0147]    As a particularly preferred option, the plastic is injected with a slight oversize or through a particular mold in the region of the dividing walls in such a way that the dividing walls are clamped by the plastic when pressed into the piston main body. 
         [0148]    The mold for the plastic can also have latching hooks and the like in order to allow simple fixing in the piston main body. The piston rod or dividing walls can likewise be fastened. 
         [0149]    It is not absolutely necessary that the divider  2  should influence the entire flow of the magnetorheological fluid along the resulting flow passage  3 ,  4 . The structure can also have one or more flow passages which can extend outside and/or inside the subassembly. 
         [0150]    It is not absolutely essential that a plurality of dividing plates  12  within one variant should have the same dimensions. They can also be different. 
         [0151]    It is also possible for a core  20  to be constructed from a multiplicity of flow passages with dividing plates  12 . 
         [0152]    In all the embodiments, at least one dividing wall  11  can also be made a fixed component part of the field closing device  9  or of the magnetic field generating device  8  by means of at least one narrow web, without being restricted thereto, if said web is produced by wire cutting, precision casting or a similar method for producing fine structures, for example. 
         [0153]    The magnetic field does not always have to be closed via the field closing device  9 , as illustrated in  FIG. 2  for example, but can be closed exclusively via component  43  (cylinder . . . ). For example, the piston shown in  FIG. 8  can run directly in a cylinder, without a rear collar  46 . The magnetic field can also be closed via the field closing device  9  and component  43  (cylinder . . . ). In that case, however, the cylinder  43  must have at least partially ferromagnetic properties. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  subassembly 
           2  divider 
           3  flow passage 
           4  flow passage 
           5  flow path 
           6  flow path 
           7  component 
           8  magnetic field generating device 
           9  field closing device 
           10  solidifying medium 
           11  dividing wall 
           12  dividing plate 
           13  latching device 
           14  latching tooth 
           15  flow direction 
           16  width 
           17  height 
           18  length 
           19  electric coil device 
           20  core 
           21  longitudinal axis 
           22  constriction 
           23  coil holder 
           24  pole cap 
           25  pole cap 
           26  axis 
           27  insert 
           28  stack 
           29  placeholder 
           30  piston 
           31  piston guide 
           32  piston rod 
           33  longitudinal axis 
           34  latching means 
           35  piston main body 
           36  dividing template 
           37  dividing template 
           38  cable 
           39  shallow cross section 
           40  mold 
           41  dividing piston 
           42  compensating space 
           43  housing 
           44  assembly hole, bypass passage 
           45  undercut, groove 
           46  offset 
           47  thickness 
           48  collecting space 
           49  opening 
           50  damper 
           51  seal