Patent Publication Number: US-2017350467-A1

Title: Damper

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of German Patent Application Serial No. 10 2016 209 826.8 filed Jun. 3, 2016, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
     FIELD OF THE INVENTION 
     The invention relates to a damper. 
     BACKGROUND OF THE INVENTION 
     A damper is known from DE 10 2010 029 180 A1. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to develop a damper such that the settability of a damping action of the damper is improved. 
     This object is achieved according to the invention by a damper comprising a housing having a working chamber; damping fluid located in the working chamber; a piston unit arranged in the working chamber, having a piston rod having a longitudinal axis, a piston fastened to the piston rod, said piston subdividing the working chamber into a first working chamber part and into a second working chamber part, a through-flow duct connecting the first working chamber part and the second working chamber part; an adjusting unit for adjusting the damping force of the damper, having an adjusting element for adjusting the effective flow cross-sectional area of the through-flow duct, an adjusting actuator for automatically adjusting an arrangement of the adjusting element and of the piston rod, a force transmission device for transmitting an actuating force provided by the adjusting actuator, wherein the adjusting actuator is arranged outside the housing. 
     According to the invention, it has been found that an adjusting unit for adjusting a damping force of a damper has an adjusting actuator which is arranged outside a housing of the damper. The adjusting unit furthermore has an adjusting element for adjusting the effective flow cross-sectional area of a through-flow duct, and a force transmission device for transmitting an actuating force provided by the adjusting actuator to the adjusting element. By way of the adjusting actuator, an arrangement of the adjusting element and of a piston rod can be adjusted in an automated manner. The piston rod is a constituent part of a piston unit. The piston rod has a longitudinal axis. Fastened to the piston rod is a piston which subdivides a working chamber of the housing, in which damping fluid is located, into a first working chamber part and into a second working chamber part. The through-flow duct connects the first working chamber part to the second. The adjusting element is arranged in particular within the damper, in particular within the damper housing, in particular within the piston rod. The adjusting element can be embodied as a cover which covers or opens up at least some or part of the through-flow openings. The adjusting element can also be embodied as a control rod, cone valve or needle valve. What is essential is that the adjusting actuator is arranged in a manner spatially separated from the adjusting element. The damper itself, in particular the housing, can be embodied in a compact and uncomplicated manner. In particular, already existing dampers, which are embodied without an adjusting actuator, can be retrofitted to form a damper according to the invention. As a result of the functional separation of the adjusting actuator and adjusting element, various drive concepts for the adjusting actuator are possible, in order to provide a required actuating force. For example, electric, hydraulic or pneumatic adjusting actuators are possible. Depending on the embodiment of the adjusting element, the force transmission device allows a suitable transmission of the actuating force into an adjusting movement of the adjusting element. It is possible for example for a spindle drive, a linear motor, an electromagnet, a rotary magnet, a pneumatic cylinder or a hydraulic cylinder to serve as force transmission devices. Outside the housing means that not even some of the adjusting actuator is arranged within the housing. The adjusting actuator is arranged on the damper in particular at a distance from the housing. It is conceivable for the adjusting actuator to be fastened directly to an outer side of the housing or by means of additional fastening elements. The adjusting actuator can also be arranged at a distance from the housing. 
     A control unit with a control unit which has a signal link to the adjusting unit, for the controlled adjustment of the effective flow cross-sectional area of the through-flow duct, ensures targeted setting of the damping action. The control unit has in particular a signal link to the adjusting unit. 
     Rotatability of the adjusting element and the piston rod relative to one another about the longitudinal axis allows the damping force to be influenced directly. 
     The rotatability of the adjusting element, which is in particular drivable in rotation, about the longitudinal axis involves reduced retrofitting effort. 
     Rotatability of the piston rod, which is in particular drivable in rotation, about the longitudinal axis allows simplified transmission of rotation to the piston rod. 
     An adjusting lever of the adjusting element, said adjusting lever being oriented transversely, in particular radially, with respect to the longitudinal axis, allows a simplified coupling of the adjusting actuator to the adjusting element via the force transmission device. 
     Articulation of the force transmission device directly to the adjusting lever allows improved force transmission. 
     A pivot lever of the force transmission device, said pivot lever being pivotable about a pivot, in particular a pivot fixed to the damper, said pivot lever being connected at a first end to the adjusting actuator and at a second end to the adjusting lever simplifies retrofitting of the damper. In particular, the pivot lever is articulated to the damper in a pivotable manner about a pivot fixed to the damper. 
     A pulling element, in particular in the form of a Bowden cable, of the force transmission device, said pulling element being in particular a Bowden cable, which connects the pivot lever to the adjusting actuator, allows uncomplicated coupling of the adjusting actuator to the adjusting element. A Bowden cable is a common force transmission means, in particular for transmitting tensile loads. The pulling element, in particular the Bowden cable, is also suitable for transmitting compressive loads. For this purpose, the Bowden cable is embodied with an inner cable which is guided in an outer, comparatively rigid sheath. It is advantageous for the pivot lever to be pivotable in a spring-mounted manner such that, when the pulling element is not transmitting any actuating force, the pivot lever is moved back into an inactivated starting position on account of the spring restoring force. 
     An adjusting actuator embodied as a rotary drive, in particular as an electric motor, allows uncomplicated and direct provision of the actuating force. 
     A damper having a toothing, which corresponds to a counterpart toothing on the adjusting element, is embodied in a particularly compact manner. 
     A damper having a gear wheel, which is arranged in particular directly on the output shaft of the adjusting actuator, is embodied in a particularly robust manner. 
     A rack on which the counterpart toothing is embodied, said rack being coupled, in particular directly coupled, to the adjusting element, in particular to the adjusting lever, simplifies the retrofitting of the damper. In particular the rack is embodied such that it can interact with an adjusting lever of an adjusting element. 
     A counterpart gear wheel on which the counterpart toothing is embodied, said counterpart gear wheel being connected to the piston rod for conjoint rotation, wherein in particular the axis of rotation of the counterpart gear wheel is identical to the longitudinal axis of the piston rod, allows the direct force transmission to the piston rod. The piston rod is driven directly by the adjusting element. 
     Further advantageous configurations, additional features and details of the invention can be gathered from the following description of exemplary embodiments with reference to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a perspective illustration of a damper according to a first exemplary embodiment, in which a force transmission device has a Bowden cable, 
         FIG. 2  shows an enlarged detail illustration of the detail II in  FIG. 1 , 
         FIG. 3  shows a longitudinal section on section line III-III in  FIG. 1  upon activation in the insertion direction, 
         FIG. 4  shows a longitudinal section corresponding to  FIG. 3  upon activation of the damper in the extension direction, 
         FIG. 5  shows an enlarged detail illustration, corresponding to  FIG. 3 , of the lower part of the damper housing according to a further embodiment, 
         FIG. 6  shows a perspective detail illustration of a damper according to a further exemplary embodiment, in which the force transmission device comprises a gear wheel and a rack, 
         FIG. 7  shows an illustration, corresponding to  FIG. 6 , of a damper according to a further exemplary embodiment, in which the force transmission device has a gear wheel and a counterpart gear wheel coupled directly to the adjusting unit, 
         FIG. 8  shows an enlarged illustration, corresponding to  FIG. 2 , of a damper according to a further exemplary embodiment, in which the force transmission device comprises a rod-like connecting element, 
         FIG. 9  shows an illustration, corresponding to  FIG. 8 , of a damper according to a further exemplary embodiment, in which the force transmission device is articulated directly to the adjusting actuator and to the adjusting unit, 
         FIG. 10  shows a perspective illustration of a damper according to a further exemplary embodiment, in which the piston rod is drivable in rotation by means of a counterpart gear wheel fastened thereto, 
         FIG. 11  shows an illustration, corresponding to  FIG. 10 , of a damper according to a further exemplary embodiment, in which the piston rod is drivable in rotation by means of an eccentric element and a connecting element, 
         FIG. 12  shows a perspective illustration in partial section of a damper according to a further exemplary embodiment, in which a motor/gear mechanism combination is held on the first fastening element, 
         FIG. 13  shows an illustration, corresponding to  FIG. 12 , of a damper according to a further exemplary embodiment, in which the adjusting lever is articulated to the motor/gear mechanism unit by means of a multiple joint hinge. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following text, a first exemplary embodiment of the invention is described with reference to  FIGS. 1 to 4 . A damper  1  has a housing  4  with a first housing end  2  and a second housing end  16 . The housing  4  is closed at the first housing end  2  by a guiding and sealing unit  3 . At the second housing end  16 , the housing  4  has a second fastening element  15 . The housing  4  encloses a working chamber  5  and a balance chamber  6 . The housing  4  has a longitudinal axis  7 . It is configured in particular at least partially in a rotationally symmetrical manner with respect to the longitudinal axis  7 . The housing  4  can be configured in a double-walled manner. It comprises in particular an inner housing  8  and an outer housing  9 . The outer housing  9  surrounds the inner housing  8 . The outer housing  9  can be arranged in particular concentrically with the inner housing  8 . The balance chamber  6  is thus configured as an annularly cylindrical cavity. 
     In an alternative variant that is not illustrated in the figures, the outer housing  9  can also be arranged in an offset manner with respect to the inner housing  8 , such that the balance chamber  6  has a variable, i.e. non-constant width along its circumference. In this case, the balance chamber  6  can be configured in particular in a topologically contractible manner. 
     The working chamber  5  is filled with a damping fluid  10 . The damping fluid  10  is in particular a hydraulic oil. The balance chamber  6  is partially filled with the damping fluid  10 . The rest of the balance chamber  6  is filled with gas, in particular with air. 
     The guiding and sealing unit  3  comprises a first sealing element  41 , which fits closely against the piston rod  12  in a sealed manner. In order to be held on the piston rod  12 , the first sealing element  41  has an annular groove  42  in which a clamping ring  43  is arranged. Furthermore, the guiding and sealing unit  3  has a supporting element  44  which is supported towards the outside on the outer housing  9 . The supporting element  44  is mounted in a sealed manner against the outer housing  9  by means of a sealing ring  45 . It has a central blind hole  46 . The guiding and sealing unit  3  has a central bore  47 . The bore  47  is arranged in particular concentrically with the longitudinal axis  7 . The piston rod  12  is guided through the bore  47 . 
     Furthermore, the damper  1  comprises a piston unit  11  having a piston rod  12  and a piston  13 . The piston  13  is fastened to the piston rod  12  and guided in the inner housing  8  so as to be movable along the longitudinal axis  7 . The piston rod  12  is guided out of the housing  4  in a manner sealed by the guiding and sealing unit  3 . At its opposite end from the piston  13 , the piston rod  12  is connected to a first fastening element  14 . The first fastening element  14  is embodied in the form of a transverse bore in a mounting plate  81 . The mounting plate  81  is firmly connected to the piston rod  12 . The mounting plate  81  is arranged in a manner fixed to the damper, in particular to the piston rod. 
     The piston  13  subdivides the working chamber  5  into a first working chamber part  17  facing the first housing end  2  and having a first working chamber end  18 , and a second working chamber part  19  facing the second housing end  16  and having a second working chamber end  20 . 
     Arranged at the first working chamber end  18  is a first terminating element  21 . The first terminating element  21  is arranged in the inner housing  8 . The first terminating element  21  can in particular be plugged into the inner housing  8 , preferably pressed or screwed in. It is sealed off from the inner housing  8  by means of a sealing ring  22 . The first terminating element  21  is configured integrally with the supporting element  44 . It is thus likewise a constituent part of the guiding and sealing unit  3 . In principle, however, it is also conceivable to configure the first terminating element  21  and the supporting element  44  as separate parts. 
     The first terminating element has a first balance duct  23 , which forms a through-flow connection, indicated in the figures by arrows, between the first working chamber part  17  and the balance chamber  6 . For further details with regard to the embodiments of the first terminating element  21 , reference is made to DE 10 2005 023 756 A1. 
     Arranged at the second working chamber end  20  is a second terminating element  24 . The second terminating element  24  is arranged in the inner housing  8 . The second terminating element  24  can in particular be plugged into the inner housing  8 , preferably pressed in. The second terminating element  24  can be held in the inner housing  8 , in the region of the second working chamber end  20 , by an encircling bead  27 . In order to improve the hold of the second terminating element  24 , the bead  27  can be reinforced by a clamping ring  28 . Furthermore, the circumference of the inner housing  8  can regionally rest against the outer housing  9  in the region of the second working chamber end  20 , in particular in the region of the bead  27 . For this purpose, the outer housing  9  has step-like reinforcements  29 , against which a bearing shoulder  30  of the inner housing  8  rests in a form-fitting manner. 
     The second terminating element  24  can be sealed off from the inner housing  8  by means of a sealing ring  25 . It has a second balance duct  26 , which forms a through-flow connection between the second working chamber part  19  and the balance chamber  6 . 
     For proper operation of the damper  1 , the working chamber  5  should always be completely filled with damping fluid  10 . This can be achieved by a suitable configuration and arrangement of the second balance duct  26  and a quantity of damping fluid  10  that is adapted to the volume of the working chamber  5  and the configuration of the balance chamber  6 . The damper  1  has in particular a preferred installation position, such that the extension direction  40  is opposed to the direction of the force of gravity. The proper operation of the damper  1  can then be ensured up to a twist angle of at least 77° out of the preferred installation position. 
     Provided in the second balance duct  26  is a balance valve  31 . The balance valve  31  comprises in particular a valve pin  32  which is pretensioned against the second terminating element  24  by means of a conically tapering valve coil spring  33 . To this end, the valve coil spring  33  bears against a valve pin stop  34 . The valve pin  32  is guided in a bore  35  in the second terminating element  24 . The bore  35  is arranged in particular concentrically with the longitudinal axis  7 . Furthermore, the balance valve  31  comprises a polygonal valve nut  36  arranged on the valve pin  32 . The valve nut  36  forms a further stop, against which a spacer washer  37  arranged on the valve pin  32  bears. Arranged in a manner bearing against the spacer washer  37  are a valve plate spring  38  and a valve disc  39 . 
     The balance valve  31  is configured as an automatic valve. It can be configured as a one-way valve. It is in particular configured such that it allows a flow from the balance chamber  6  through the second balance duct  26  into the second working chamber part  19 . In other words, the balance valve  31  is configured such that it opens when the piston  13  moves in an extension direction  40  parallel to the direction of the longitudinal axis  7 . 
     In the exemplary embodiment illustrated in  FIGS. 1 to 4 , the balance valve  31  is configured such that it allows a bidirectional flow through the second balance duct  26 . It is thus configured as a two-way valve. The balance valve  31  can in particular have impressions which, independently of the position of the valve disc  39 , enable a bidirectional through-flow between the second working chamber part  19  and the balance chamber  6 . 
     In general, provision is made for the balance valve  31  to form an overload protection element which ensures that the second balance duct  26  is open if a predetermined limit force on the piston rod  12  in the direction of the longitudinal axis  7  is exceeded. The activation characteristic of this overload protector can be achieved easily by a suitable choice and dimensioning of the valve coil spring  33  and of the valve plate spring  38 . 
     An alternative structural design of the balance valve  31  is conceivable. For further details of the balance valve  31 , reference is made to DE 10 2005 023 756 A1, in particular paragraph [0022]. 
     The piston rod  12  is configured in a multipart, in particular two-part manner. It comprises an outer piston rod sleeve  48 , formed in a tubular manner, and a piston rod core  49 . 
     The piston rod sleeve  48  can be connected to the first fastening element  14 . The first fastening element  14  has a transition fit  66  which is arranged concentrically with the longitudinal axis  7  and by way of which the first fastening element is plugged onto an outer side of the piston rod  12 , in particular of the piston rod sleeve  48 . The first fastening element  14  is connected to the piston rod  12  by a weld  67 . 
     The first fastening element  14  can alternatively have an internal thread, by means of which the first fastening element  14  is screwed onto a matching external thread on the piston rod sleeve  48 . 
     The piston rod core  49  is sealed off from the piston rod sleeve  48  by means of a sealing ring  61 . The sealing ring  61  is arranged in an annular groove  68  in the piston rod core  49 . In the region of the sealing ring  61 , the piston rod sleeve  48  is formed in a reinforced manner towards the inside, that is to say radially with respect to the longitudinal axis  7 . Here, it has a reinforcement  62 . Apart from the groove  68 , the piston rod core  49  is formed in a fully cylindrical manner in the region of the reinforcement  62 . In the region of the reinforcement  62 , the piston rod core  49  bears against the piston rod sleeve  48  in a form-fitting manner. As a result, it is mounted in the piston rod sleeve  48  without play in the radial direction. 
     The piston rod core  49  has a circular cross section in particular in the region of the reinforcement  62 . It is thus formed in a fully cylindrical manner at least in this region. 
     In an end region  69  adjoining this region counter to the extension direction  40 , the piston rod core  49  has a recess  70 . The recess  70  is formed in the form of a circle segment in the direction perpendicular to the longitudinal axis  7 . It has a centre angle. The centre angle is at least 15°, in particular at least 30°, in particular at least 45°, in particular at least 60°, in particular at least 90°. It can in particular also be 120°. At most 270°, in particular at most 180° are provided as the upper limit for the centre angle. In principle, a configuration of the recess  70  in the form of a sector of a circle is also possible. The recess can also be configured as a bore in the piston rod core  49 . 
     The piston rod core  49  is an adjusting element which is embodied in the form of a cover. The adjusting element  49 , an adjusting actuator  89  and a force transmission device  87  form an adjusting unit. 
     The adjusting unit has a signal link via the adjusting actuator  89  to a control unit  92  illustrated purely schematically in  FIG. 1 . The control unit  92  can also be embodied in a manner integrated in the adjusting actuator  89 . 
     The recess  70  is part of a through-flow duct  71  which forms a through-flow connection between the working chamber parts  17 ,  19 . In addition to the recess  70 , the through-flow duct  71  comprises a plurality of bores  72  in the piston rod sleeve  48 . In other words, the bores  72  together with the recess  70  form the through-flow duct  71 . The through-flow duct  71  is thus arranged in the piston rod  12 . Depending on the rotational position of the piston rod core  49  with respect to the longitudinal axis  7 , how many or which of the bores  72  are opened up by the recess  70  or covered is defined. This results in an effective flow cross-sectional area of the through-flow duct  71 . 
     At least one bore  72  is provided in the piston rod sleeve  48 . In the exemplary embodiment illustrated in  FIGS. 1 to 4 , the piston rod sleeve  48  has two bores  72 . It can also have three, four, five or more bores  72 . The bores  72  are each arranged in a manner offset with respect to one another in the circumferential direction. The bores  72  are all the same size. However, bores  72  with different sizes are likewise conceivable. 
     As an alternative to a plurality of discrete bores  72 , the piston rod sleeve  48  can also have a through-flow opening configured in an elongate manner. The through-flow opening extends preferably in the circumferential direction. It covers an angular range which is at most as large as the centre angle of the recess  70  in the piston rod core  49 . 
     By means of the end region  69  of the piston rod core  49 , the bores  72  are selectively closable. The end region  69  of the piston rod core  49  thus forms an adjusting element, by means of which the effective flow cross section of the through-flow duct  71  is adjustable. The adjusting element for adjusting the effective flow cross section of the through-flow duct  71  is thus arranged in the interior of the piston rod  12 , in particular in the interior of the piston rod sleeve  48 . 
     By means of the adjusting element, the through-flow duct  71  is in particular closable in order to interrupt the through-flow connection between the working chamber parts  17 ,  19 . As a result, the damper  1  is blockable. 
     A plurality of discrete bores  72  allow a plurality of different discrete damping settings of the damper  1 . The damper  1  can thus have a stepped damping characteristic. Through an advantageous arrangement of the bores  72 , it is possible to allow a continuously adjustable damping behaviour of the damper  1 , in that for example the bores  72  are arranged in an at least partially overlapping manner in an activating direction of the adjusting element  102 . The adjusting direction of the adjusting element  102  is oriented axially and/or tangentially to the longitudinal axis  7 . Likewise, an elongate opening in the piston rod sleeve  48  allows a continuously adjustable damping behaviour of the damper  1 . 
     The piston rod core  49  is displaceable, in particular rotatable, with respect to the piston rod sleeve  48 . For this purpose, it is connected to an adjusting lever  63 . The adjusting lever  63  is connected to the piston rod core  49  in the region of the first fastening element  14 . For this purpose, the first fastening element  14  has a cutout  64 . The adjusting lever  63  is arranged in particular in a bore  65  in the piston rod core  49 . The bore  65  extends perpendicularly to the longitudinal axis  7 . The adjusting lever  63  is pressed into the bore  65 . Alternatively, provision can be made to provide the adjusting lever  63  with an external thread and the bore  65  with a matching internal thread. The adjusting lever  63  can in particular be screwed into the piston rod core  49 . This allows particularly easy assembly. Furthermore, this allows easy exchangeability of the adjusting lever  63  and of the piston rod core  49 . It is also conceivable to configure the piston rod core  49  to be displaceable with respect to the piston rod sleeve  48 . 
     The adjusting lever  63  can bear against the piston rod sleeve  48  in the direction of the longitudinal axis  7 . It thus fixes the piston rod core  49  so that it is prevented from being displaced unintentionally counter to the extension direction  40  relative to the piston rod sleeve  48 . Fixing of the piston rod core  49  in the piston rod sleeve  48  so that it is prevented from being displaced with regard to the longitudinal axis  7  can also be achieved with alternative, separate fixing means. 
     A pivot lever  82  is articulated to the mounting plate  81  so as to be pivotable about a pivot  83 . The pivot lever  82  is embodied substantially in an L-shaped manner with a first lever arm  84  and a second lever arm  85 . The lever arms  84 ,  85  intersect at the apex of the pivot lever  82 . The pivot  83  extends through the apex of the pivot lever  82 . 
     A connecting element  86 , which acts on the adjusting lever  63 , is articulated to a free end of the first pivot arm  84 , which is arranged opposite the pivot  83 . 
     The pivotability of the pivot lever  82  about the pivot  83  is embodied in particular in a spring-mounted manner, wherein the illustration according to  FIG. 1  shows the pivot lever  82  in a starting arrangement. Upon activation of a pulling element in the form of a Bowden cable  87 , the internal wire of the Bowden cable is extended out of the outer sheath and thus the pivot lever  82 , in particular the second lever arm  85 , is rotated anticlockwise with respect to the pivot  83 . The first lever arm  84  is correspondingly rotated anticlockwise about the pivot  83 . Via the connecting element  86 , the adjusting lever  63  is rotated and thus adjustment of the damping action in the manner outlined below is allowed. 
     A pulling element in the form of a Bowden cable is articulated to the free end of the second lever arm  85 , which is arranged opposite the apex of the pivot lever  82 . The sheath of the pulling element is fixed in a holder  88 , provided for this purpose, on the mounting plate  81 . At an opposite end, away from the mounting plate  81 , the pulling element is articulated to an adjusting actuator  89 . According to the exemplary embodiment shown, the adjusting actuator  89  is embodied by a motor/gear mechanism unit  90 , to the drive shaft of which an eccentric element  91  is articulated. 
     The pulling element is a force transmission device. 
     An essential advantage of this exemplary embodiment is that the damper and in particular the adjustment of the damping action can be ensured in an uncomplicated manner, in particular by means of known components. The damper can in particular be retrofitted in an uncomplicated manner. The Bowden cable  87  can in particular be arranged substantially freely, taking the bending radii to be complied with into consideration. In particular, it is conceivable to arrange the Bowden cable in a space-saving manner in the available installation space. This results in additional degrees of freedom in the arrangement of the Bowden cable. The Bowden cable is part of a force transmission device which serves to transmit the actuating force provided by the adjusting actuator  89 . The adjusting actuator  89  is arranged outside and at a distance from the housing  4  of the damper  1 . 
     At a first piston rod end  50  arranged in the inner housing  8 , the piston rod sleeve  48  has a reduced outside diameter, thereby forming a piston rod stop  51 . Starting from the piston rod stop  51 , a first spacer washer  52 , a first closure element  53 , in particular in the form of a plate spring, a piston disc  54 , a second closure element  55 , in particular in the form of a plate spring, a second spacer washer  56  and a securing nut  57  are arranged on the piston rod sleeve  48  in the region of the first piston rod end  50 . The securing nut  57  is screwed onto a piston rod thread and secures the piston  13  on the piston rod  12 . The piston  13  is formed by the first closure element  53 , the piston disc  54 , the second closure element  55  and a piston seal  58 . The piston seal  58  is configured in an annular manner and arranged in an annular groove  59  in the piston disc  54 . The piston seal  58  thus seals the piston disc  54  off from the inner housing  8 . 
     Provided in the piston disc  54  are a plurality of through-flow ducts  60 . The through-flow ducts  60  form a through-flow connection between the first working chamber part  17  and the second working chamber part  19 . The closure elements  53 ,  55  each interact with at least one of the through-flow ducts  60 . They can also interact with a plurality of the through-flow ducts  60 . They can act in particular as valve elements and influence the efficient flow cross section of the through-flow ducts  60 , depending on a direction and/or speed of movement of the piston  13  with respect to the extension direction  40 . They can in particular be configured such that only a unidirectional flow through the through-flow ducts  60  is possible. In this case, the closure elements  53 ,  55  form a one-way valve. The closure elements  53 ,  55  can in particular be configured such that they open when a particular limit force is exceeded. In this case, they form an overload protector. 
     An alternative embodiment of the piston  13  is conceivable. In this regard, for further details with regard to the through-flow duct  60  and the closure elements  53 ,  55 , reference is made to the description of DE 10 2005 023 756 A1, in particular paragraphs [0023] et seq. It is in particular also possible to configure the piston  13  in a sealed manner, that is to say without through-flow ducts  60 . In this case, the working chamber parts  17 ,  19  are separated in a fluid-tight manner by the piston  13 . In this case, the through-flow duct  71  in the piston rod  12  forms the only direct through-flow connection between the working chamber parts  17 ,  19 . 
     In the following text, the adjustability of the effective flow cross section of the through-flow duct  71  by means of the end region  69 , forming the adjusting element, of the piston rod core  49  is described. The adjusting element is able to be activated by way of a movement with respect to the longitudinal axis  7 , in particular by rotation. It is likewise conceivable to provide an adjusting element that is able to be activated by displacement with respect to the longitudinal axis  7 . The adjusting element is in particular able to be activated by means of the adjusting lever  63 . In a first adjusting position, the end region  69  of the piston rod core  49  does not cover either of the bores  72 . Both bores  72  thus contribute towards the effective flow cross section of the through-flow duct  71 . In other words, the through-flow duct  71  has its greatest possible effective flow cross section. The damping of a movement of the piston rod  12  is at a minimum, that is to say the resistance to such a movement in or counter to the extension direction  40  is as low as possible. In this adjusting position, the damper  1  exhibits its softest possible damping. 
     In a further adjusting position, the end region  69  of the piston rod core  49  covers one of the bores  72 , while the other remains open. As a result, the effective flow cross section is reduced by half compared to the adjusting position illustrated in  FIGS. 3 and 4 . The damping of the damper  1  is thus harder. 
     In a further adjusting position, the end region  69  of the piston rod core  49  covers both, that is to say all of the bores  72 . The through-flow duct  71  is closed in this position. Its effective flow cross section is zero. The through-flow connection between the working chamber parts  17 ,  19  through this through-flow duct  71  is interrupted. A through-flow connection for the damping fluid  10  between the working chamber parts  17 ,  19  is provided at most via the balance ducts  23 ,  26  and the balance chamber  6 . The damping of a movement of the piston rod  12  is at a maximum in this adjusting position, that is to say that the resistance to a movement of the piston rod  12  in or counter to the extension direction  40  is as high as possible. In this adjusting position, the damper  1  exhibits its hardest possible damping. It can in particular be blocked. 
     With regard to the embodiment of the piston rod  12  with the piston rod core  49  and the piston rod sleeve  48  and to the function thereof for adjusting the adjusting unit, reference is made to DE 10 2010 029 180 A1. What is essential is that the adjusting lever  63 , by means of which the adjusting element  49  is rotated about the longitudinal axis  7  in the piston rod  12 , is able to be activated in an automated and in particular controlled manner via the force transmission device  87  and the adjusting actuator  89 . 
     The function of the damper  1  is described in the following text. In the adjusting position, illustrated in  FIGS. 3 and 4 , of the adjusting element, the through-flow duct  71  in the piston rod  12  is opened to a maximum. In the event of a movement of the piston  13  counter to the extension direction  40 , the damping fluid  10  can thus flow from the second working chamber part  19 , through the through-flow duct  71  in the piston rod  12 , and into the first working chamber part  17 . Furthermore, the damping fluid  10  displaced out of the working chamber  5  by the additional volume of the piston rod  12  can flow into the balance chamber  6  through the first balance duct  23 . 
     Provision is made for the second balance duct  26  to be as closed as much as possible in the event of small forces, directed counter to the extension direction  40 , on the piston rod  12 , in particular at low speeds of the piston  13  counter to the extension direction  40 . In a balance valve  31  which allows bidirectional flow through the second balance duct  26 , the balance valve  31  is not completely closed. On account of the impressions, a bidirectional flow through the second balance duct  26  is always possible. However, in principle, it is also possible for the balance valve  31  to be configured as a one-way valve which is in a blocking position in the event of small forces, directed counter to the extension direction  40 , on the piston rod  12 . The response behaviour of the balance valve  31  is determined by a suitable choice and setting of the valve coil spring  33  and of the valve plate spring  38 . 
     In a corresponding manner, the through-flow duct  60  in the piston  13  can be closed by the first and/or second closure element  53 ,  55  at low speeds of the piston  13 . 
     In the event of a movement of the piston  13  in the extension direction  40 , the damping fluid  10  can flow from the first working chamber part  17 , through the through-flow duct  71  in the piston rod  12 , and into the second working chamber part  19 . Furthermore, the balance valve  31  opens and allows damping fluid  10  to flow out of the balance chamber  6 , through the second balance duct  26 , and into the second working chamber  19 . This ensures that the working chamber  5  is always completely filled with damping fluid  10 , apart from the volume displaced by the piston unit  11 . 
     The balance valve  31  in the second termination element  24  and/or the closure elements  53 ,  55  in the piston  13  can be configured such that, in the event of a movement of the piston rod  12  in the extension direction  40 , damping fluid  10  flows through the second balance duct  26  in the second termination element  24  and/or the through-flow duct  60  in the piston  13  only in the event of a high extension speed of the piston rod  12  or a large force on the latter in the extension direction  40 . 
     The through-flow duct  60  in the piston  13  and/or the balance valve  31  in the second termination element  24  thus act as an overload protector which is triggered at high speeds and/or large forces on the piston rod  12  and thus prevents the damper  1  from being damaged. Of course, the damping behaviour of the damper  1  can be influenced as desired by a suitable choice of the closure elements  53 ,  55  of the through-flow duct  60  and/or of the valve elements  33 ,  38  of the balance valve  31 . 
     As a result of the piston rod core  49  being rotated about the longitudinal axis  7  by means of the adjusting lever  63 , the bores  72  of the through-flow duct  71  in the piston rod  12  can be closed by the end region  69  of the piston rod core  49 . As a result, the effective flow cross section of the through-flow duct  71  in the piston rod  12  is reduced, in particular closed, in particular completely closed. It is then no longer possible for damping fluid  10  to flow out of the first working chamber part  17 , through the through-flow duct  71 , and into the second working chamber part  19  or vice versa. 
     Inasmuch as the balance valve  31  prevents damping fluid  10  from flowing out of the second working chamber part  19  and into the balance chamber  6 , the piston rod  12  is blocked so that it cannot be displaced counter to the extension direction  40  in this position of the adjusting element formed by the piston rod core  49 , in particular the end region  69  thereof, on account of the completely closed volume of the second working chamber part  19 . 
     However, if the force on the piston rod  12  exceeds a predetermined limit force in the direction counter to the extension direction  40 , the overload protector is activated and the through-flow duct  60  in the piston  13  and/or the second balance duct  26  in the second termination element  24  is opened. 
     Since the balance valve  31  in the second termination element  24  opens in the event of a movement of the piston  13  in the extension direction  40 , in order to allow damping fluid  10  to flow out of the balance chamber  6  and into the second working chamber part  19 , and the first balance duct  23  in the first termination element  21  is closed, the damper  1  is not completely blocked so as to prevent the piston rod  12  from moving in the extension direction  40 , even in the case of a closed through-flow duct  71  in the piston rod  12 . However, it exhibits maximum hard damping, since the damping fluid  10  cannot flow from the first working chamber part  17  into the second working chamber part  19  through the through-flow duct  71  in the piston rod  12 , but rather flows from the first working chamber part  17  into the balance chamber  6  and from the balance chamber  6  through the second balance duct  26  into the second working chamber part  19 . Thus, in this case, the damping characteristic is determined by the balance ducts  23 ,  26  and, in particular, by the balance valve  31 . 
     In an alternative embodiment, provision can be made for the closure elements  53 ,  55  to be configured such that the through-flow ducts  60  in the piston  13  open or close depending on the speed of the movement of the piston rod  12  in the extension direction  40 . As a result, a speed-dependent damping characteristic can be achieved. For details in this regard, reference is made to DE 10 2005 023 756 A1, paragraphs [0028] et seq. 
     In an alternative embodiment of the second termination element  24  according to the embodiment shown in  FIGS. 3 and 4 , the second termination element  24  can be axially supported at the end against the inner housing  8  by way of an abutment shoulder  100  and be radially supported against the inner cylindrical lateral surface of the inner housing  8  by way of a plug-in collar  101 . The plug-in collar  101  is pretensioned radially with respect to the longitudinal axis  7  by means of a radial spring element  102 , wherein the pretensioning is applied axially by means of a clamping nut  103  on a clamping bolt  104 . In the region in which the plug-in collar  101  bears against the inner cylindrical lateral surface of the inner housing  8 , the inner housing  8  is pressed radially outwards against an inner side of the outer housing  9  and as a result held. 
     In a further embodiment that is not illustrated, an additional switching element can be provided, which closes at least one of the balance ducts  23 ,  26  or both balance ducts  23 ,  26  depending on the activation direction of the damper  1 . Such a switching element is known from DE 10 2010 029 180 A1, to which reference is hereby made, in particular to FIG. 9 of DE 10 2010 029 180 A1, and corresponding US 2011/0284333 A1, the entire contents of which are hereby incorporated by reference. 
     In the case of an interruption to the power supply, the position detection unit  107  ensures that the position detection is reset by means of a reference move. To this end, in particular a reference mark, which can be embodied for example as a stop element, is used. This ensures that, following an unforeseen interruption to the movement of the adjusting element, the position thereof can be established and fixed clearly and in an uncomplicated manner. 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 6 . Identical parts are provided with the same reference signs as in the first exemplary embodiment, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by an a. 
     According to the exemplary embodiment shown, the adjusting actuator  89   a  is embodied with a motor/gear mechanism unit  90   a  as rotary drive. A gear wheel  94  is arranged coaxially, as part of the force transmission device, on an output shaft  93  of the electric motor  90   a . The gear wheel  94  has a toothing which corresponds to a counterpart toothing of the adjusting element in the form of a rack  95 . The rack  95  has, on an underside located away from the counterpart toothing, a substantially V-shaped recess  96  in which the adjusting lever  63  is arranged. 
     The force transmission device acts directly on the adjusting lever  63 . The force transmission device, in particular the rack  95  with the recess  96 , acts directly on the adjusting lever  63 . 
     In the exemplary embodiment according to  FIG. 6 , the adjusting actuator  89   a  is fastened directly to the mounting plate  81   a.    
     In order to adjust the damping action of the damper  1   a , the adjusting actuator  89   a  is activated. Depending on the direction of rotation of the electric motor  90   a , the gear wheel is rotated clockwise or anticlockwise and this rotary movement is transmitted directly to the rack  95 . With respect to the longitudinal axis  7 , the rack  95  is moved perpendicularly thereto. As a result of the transverse movement of the rack  95 , the adjusting lever  63  arranged in the recess  96  is carried along and thus the adjustment of the damping action is brought about in the above-described manner. 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 7 . Identical parts are provided with the same reference signs as in the first exemplary embodiment, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by a b. 
     The essential difference with respect to the previous exemplary embodiment is that, in the case of the damper  1   b , the counterpart toothing of the force transmission device is embodied on a counterpart gear wheel  97 . The counterpart gear wheel  97  is embodied in particular in the form of a gear wheel segment with an opening angle range of about 90° with respect to the longitudinal axis  7 . Such an opening angle range is sufficient to allow the necessary rotation of the piston rod core  49  in the piston rod sleeve  48 . The embodiment of the counterpart gear wheel  97  as a gear wheel segment is space-saving. The counterpart gear wheel  97  is connected to the piston rod core  49  for conjoint rotation. In particular, the axis of rotation of the counterpart gear wheel  97  is identical to the longitudinal axis  7  of the piston rod  12 . 
     The coupling of the counterpart toothing to the adjusting element is embodied in a particularly robust manner as a result. A separate adjusting lever can be dispensed with. 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 8 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by a c. 
     The embodiment corresponds substantially to the first embodiment according to  FIG. 1 , wherein, instead of the Bowden cable, a second connecting element  98  is articulated in a pivotable manner to the second lever arm  85   c  of the pivot lever  82   c . By way of a free end away from the pivot lever  82   c , the second connecting element  98  is articulated directly to an eccentric element  91   c  on a motor/gear mechanism unit  90   c.    
     According to the exemplary embodiment shown, it is possible to attach the adjusting actuator  89   c  directly to the mounting plate  81   c . The installation space required is reduced. The embodiment shown is able to be retrofitted in an uncomplicated and direct manner in the case of the damper  1   c , in that the Bowden cable is replaced by the second connecting element  98  and the adjusting actuator  89   c.    
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 9 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by a d. 
     The exemplary embodiment shown corresponds substantially to the exemplary embodiment according to  FIG. 8 , wherein the eccentric lever  91   d  acts directly on the adjusting lever  63  via the connecting element  86 . The pivot lever can thus be dispensed with. The number of components and in particular the installation space required for the damper  1   d  are reduced. 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 10 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by an e. 
     This embodiment corresponds substantially to the embodiment with a gear wheel and counterpart gear wheel element according to  FIG. 7 . The essential difference according to the exemplary embodiment shown is that the counterpart gear wheel  97   e  is not directly coupled to the piston rod core  49 , i.e. to the adjusting element, but to the piston rod sleeve  48  of the piston rod  12 . The actuating force of the adjusting actuator  89   e  brings about an immediate adjustment of the piston rod  12  with respect to the longitudinal axis  7  via the gear wheel  94   e  and the counterpart gear wheel  97   e . In the damper  1   e , the piston rod core  49  is embodied in a fixed manner, wherein the piston rod sleeve  48  can rotate about the piston rod core  49  with respect to the longitudinal axis  7 . Additional force transmission elements can be dispensed with, since the actuating movement is transmitted directly by the adjusting actuator  89   e.    
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 11 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by an f. 
     The damper  1   f  according to  FIG. 11  corresponds substantially to the one according to  FIG. 10 , wherein the adjusting actuator  89   f  is embodied as a motor/gear mechanism unit  90   f  and an eccentric lever  91   f  articulated thereto. The eccentric lever  91   f  is connected to an eccentric disc  99  by means of the connecting element  86   f . The connecting element  86   f  is articulated eccentrically to the eccentric disc  99  with respect to the longitudinal axis  7 . A movement of the eccentric element  91   f  brings about eccentric force transmission to the eccentric disc  99  via the connecting element  86   f . The eccentric disc  99  is connected to the piston rod  12  for conjoint rotation. As a result of an actuation of the adjusting actuator  89   f , the piston rod  12  is rotated with respect to the longitudinal axis  7 , as in the previous exemplary embodiment. 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 12 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by a g. 
     In the damper  1   g  according to  FIG. 12 , the adjusting lever  63  is received in an opening in the counterpart gear wheel  97   g . The counterpart gear wheel  97   g  cooperates with the gear wheel  94   g  in order to allow the adjusting lever  63  to rotate with respect to the longitudinal axis  7  of the damper  1   g.    
     The gear wheel  94   g  transmits the rotary movement of a coaxially arranged drive gear wheel  106  to a reduction gear stage  105 . The reduction gear stage  105  comprises a pinion gear  107  which is arranged on an output shaft of a gear mechanism  108 . 
     The gear mechanism  108  is arranged coaxially with a motor, in particular an electric motor  109 , on which an encoder  110  is provided. The encoder  110  is arranged at a first end of the electric motor  109 , which is arranged opposite the second end, at which the gear mechanism  108  is arranged. The gear mechanism  108 , the motor  109  and the encoder  110  can be arranged in a space-saving manner in a cylindrical housing  111  along the longitudinal cylinder axis, which is oriented in particular parallel to the longitudinal axis  7  of the damper  1   g.    
     Signal transmission cables  112  and/or power cables for signal transmission or power supply are connected to the encoder  110 . The motor  109 , the gear mechanism  108  and the encoder  110  form a common motor/gear mechanism unit which is fastened releasably, by means of a plate-like fastening unit  113 , to the first fastening element  14  by means of a screw connection  114 . 
     A further exemplary embodiment of the invention is described in the following text with reference to  FIG. 13 . Identical parts are provided with the same reference signs as in the first exemplary embodiments, to the description of which reference is hereby made. Structurally different, but functionally identical parts are provided with the same reference signs followed by an h. 
     The damper  1   h  has a motor/gear mechanism unit  108 ,  109 ,  110  which is accommodated in a housing  111 . A multiple joint hinge  116  is articulated to the output shaft  115  of the gear mechanism  108 . The multiple joint hinge  116  comprises a first hinge lever  117 , which is articulated pivotably by way of its first end to the output shaft  115 . At an opposite end, the first hinge lever  117  is connected to a second hinge lever  119  of the multiple joint hinge  116  so as to be pivotable about an internal hinge axis  118 . 
     At a second end, located opposite the internal hinge axis  118 , the second hinge lever  119  is connected to the adjusting lever  63  in an articulated manner. As a result of the activation of the motor/gear mechanism unit, the multiple joint hinge  116  is pivoted directly via the output shaft  115 , from which a pivoting movement for the adjusting lever  63  can be derived directly. 
     In the exemplary embodiment according to  FIG. 13 , the fastening unit  113   h  is able to be arranged in a releasable manner on the first fastening element  14  by means of a screw (not illustrated) of a screw fastener.