Abstract:
A suspension fork of a bicycle includes at least one stanchion tube and a slider tube interacting therewith and a wheel receiving space adjacent thereto, and a damper system. The damper system includes a shut-off valve to adjust a lockout in the rebound stage and a shut-off valve to adjust a lockout in the compression stage, and one joint adjusting element. Using the joint adjusting element, the locking of the rebound stage and locking of the compression stage can be adjusted.

Description:
BACKGROUND 
       [0001]    The present invention relates to a suspension fork for a bicycle and to a damper system for a stanchion tube of a suspension fork of a bicycle. 
         [0002]    Employing suspension forks in bicycles has basically been known for a long time. Suspension forks configured in particular as telescopic suspension forks are installed in downhill and mountain bikes and in cross-country bikes, and increasingly in everyday bicycles as well. 
         [0003]    Most suspension forks comprise two tubes stationary relative to the bicycle frame, the so-called stanchion or inner tubes, and two lower, movable tubes to which the wheel hub is fastened. The stanchion tubes are held together by means of a fork bridge or fork crown at the center of which the fork column is attached. The lower, movable tubes are the so-called slider tubes or outer tubes. 
         [0004]    The riders of suspension fork-equipped bicycles desire suspension forks whose springing and damping characteristics can be easily and quickly adjusted to speedily adapt the current suspension fork characteristics to actual ambient conditions. 
         [0005]    In some situations mountain-bike riders may for example wish to disable the springing and damping characteristics or a compression of the suspension fork to reduce the inclination angle of the bicycle when climbing steep inclines to thus achieve safer riding properties and a more comfortable position on the bicycle. 
         [0006]    An increasing compression of the suspension fork is achieved by way of activating a shut-off valve with which to lock the fluid path in the rebound stage so as to allow the damping fluid to flow only in the compression stage whereby the suspension fork continues to compress in the subsequent damping movements but rebound is prohibited until the suspension fork is compressed entirely. 
         [0007]    The drawback of these kinds of system is that in some situations it is not desirable for the suspension fork to compress completely since the change of the total geometry of the bicycle will be too disagreeable. Thus the trail angle and the steering angle will change unfavorably. 
         [0008]    On the basis of the described prior art it is thus the object of the present invention to provide a suspension fork and a damper system for a stanchion tube of a suspension fork so as to allow a flexible and simple operation. 
       SUMMARY 
       [0009]    The suspension fork according to the invention for a bicycle comprises at least one stanchion tube and at least one slider tube interacting therewith and a wheel receiving space adjacent thereto provided to accommodate a wheel and in particular a front wheel of a bicycle. Furthermore, the suspension fork comprises at least one damper system. The damper system comprises at least one shut-off valve to lock the rebound stage and at least one shut-off valve to lock the compression stage. Furthermore, a joint adjusting element is provided wherein said joint adjusting element allows to adjust or activate the locking of the rebound stage and locking of the compression stage. 
         [0010]    The suspension fork according to the invention has many advantages. One considerable advantage of the suspension fork according to the invention is that both a shut-off valve for the rebound stage and a shut-off valve for the compression stage are provided. By way of activating the shut-off valve for the rebound stage and concurrently activating the shut-off valve for the compression stage, a virtually rigid suspension fork is provided in which neither compression nor rebound are possible. A particular advantage is the joint adjusting element with which to adjust both the shut-off valve for the rebound stage and the shut-off valve for the compression stage. Thus, one joint adjusting element allows to activate and deactivate both shut-off valves by way of one movement. 
         [0011]    One shared adjusting element at the suspension fork offers considerable advantages also in view of reliability and a simple structure. For example, if several, separate adjusting elements were provided at the suspension fork and they were remotely controlled via Bowden cables, these several elements might possibly be actuated by one shared operating element at the handlebar. There is the drawback in such an implementation, however, that mounting Bowden cables is complicated and furthermore that the risk of sources of errors increases. Furthermore, these kinds of cables require regular maintenance and possibly lubrication. In contrast thereto, a shared adjusting element according to the invention at the suspension fork, which immediately acts on the shut-off valves to lock the compression stage and the rebound stage, is more reliable, simpler in operation and less complicated in mounting. 
         [0012]    The suspension fork according to the invention achieves particular ease of operation and flexibility of use. Operating the joint adjusting element allows to adjust all of the lock-out or locking functions. This allows fixing and locking the suspension fork in any desired compression and rebound position so as to prohibit any further compression or rebound action. Thus, the user may actuate both the shut-off valves during a ride and thus prohibit the passage of the damping medium in the direction of the rebound stage and in the direction of the compression stage so as to arrest the suspension fork in the current position. 
         [0013]    Since the rider may actuate the joint operating element or adjusting element during a ride, the rider may thus basically fixate the suspension fork in any desired compressing position. This allows the rider to fixate the suspension fork in the desired compressed position in riding up a steep hill in that when riding uphill the rider first activates the rebound stage lockout or the rebound stage lock and as the desired compressed depth is reached, the compression stage lockout or the compression stage lock. 
         [0014]    A shut-off valve to lock the compression stage or the rebound stage is also referred to as a lockout valve that serves to activate a lockout or to lock the compression stage or the rebound stage in which the flow through the respective valve is prohibited. 
         [0015]    The joint adjusting element is in particular provided in an upper region of the suspension fork and in particular in an upper region of the stanchion tube or the stanchion tubes. Particularly preferably the joint adjusting element is disposed at an upper region of the damper system and preferably fixedly connected therewith. 
         [0016]    The damper system is in particular incorporated in a stanchion tube wherein it may be conceivable for the damper system to be partially disposed in both of the stanchion tubes or to be partially located in the connector connecting the two stanchion tubes, if two stanchion tubes are provided. The connector is in particular configured as a fork crown and receives the stanchion tubes at or in the region of the two lateral ends while a fork column is disposed in a center region. It is also conceivable for the suspension fork to comprise one stanchion tube only at the lower end of which the wheel is disposed. 
         [0017]    In a preferred specific embodiment the damper system comprises at least one movable piston which divides a damper chamber of the damper system into a first chamber and a second chamber. Above the damper chamber a control section is in particular provided at the damper system which control section in particular abuts the first chamber of the damper chamber. 
         [0018]    The damper system is in particular inserted in a stanchion tube wherein the control section is provided at an upper end of the stanchion tube and is accessible from the upper end or projects from the upper end. In the other stanchion tube, the suspension system of the suspension fork may be provided. Or else it is conceivable for both the damper system and the suspension system to be provided in one stanchion tube. 
         [0019]    The control section is in particular provided with the damper valves of the damper system such that the heat generated in damping is generated in the upper control section where it can readily dissipate to the ambience. 
         [0020]    The adjusting element may be disposed at a stanchion tube or at the connector. The joint adjusting element is in particular provided movable and in particular pivotal. 
         [0021]    Preferably, the adjusting element may be moved to a position in which it activates and in particular closes the shut-off valve for the rebound stage and it may be moved to another position in which the joint adjusting element activates the shut-off valve for the rebound stage. Particularly preferably, the joint adjusting element may be moved to a further position in which the shut-off valve for the rebound stage and the shut-off valve for the compression stage are activated. Activating is presently understood to mean, closing or substantially closing the respective valve. 
         [0022]    In all the configurations the adjusting element is in particular provided to be rotatable and it may be moved from a first rotational position or rest position, in which both of the shut-off valves are open, to different rotational positions. 
         [0023]    Advantageously, the shut-off valve for the rebound stage is activated in a second rotational position. Advantageously, both the shut-off valve for the rebound stage and the shut-off valve for the compression stage are activated in a third rotational position. In a conceivable fourth rotational position only the shut-off valve for the compression stage is activated. 
         [0024]    During rotational movement of the joint adjusting element, the shut-off valve for the rebound stage is preferably first activated and subsequently both of the shut-off valves are jointly activated such that as a desired compressed position is achieved the rider moves the joint adjusting element to the rotational position in which both shut-off valves are activated or closed. 
         [0025]    Advantageously, the movable piston is in particular fixedly connected with a slider tube via a piston rod. Since in this configuration the control elements are provided at the top surface of the stanchion tubes or on the fork crown, and since preferably the damping elements are also provided in an upper region of the stanchion tubes, the piston rod may be configured as a simple element that projects from the damper chamber downwardly into the slider tube with which it is fixedly connected. This allows a particularly simple construction and a simple structure of the suspension fork according to the invention. 
         [0026]    Preferably, a pair of spaced-apart stanchion tubes and at least one connector connecting the two stanchion tubes above the wheel receiving space are provided. 
         [0027]    In all of the embodiments it is preferred for the stanchion tube or the stanchion tubes to consist of a metal or a metallic alloy at least in part wherein the slider tube or the slider tubes may likewise consist of a metal or a metallic alloy. It is also preferred for the at least one slider tube to consist of a fibrous composite material at least in part so as to allow high strength with a reduced weight. 
         [0028]    Advantageously, the control section is provided with at least one adjustable damper valve for adjusting the rebound stage damping and at least one adjustable damper valve for adjusting the compression stage damping. By means of the control section being disposed in particular in an upper region, simple operation of the suspension fork is allowed and an uncomplicated structure is allowed since the control elements for controlling the damper valves may be provided in the vicinity of the adjustable damper valves. 
         [0029]    In particular, at least one of the adjustable damper valves is a low-speed damper valve so as to allow adjusting the damping characteristics of the suspension fork in a normal riding operation. 
         [0030]    Preferably, at least one high-speed damper valve for rebound damping and/or compression damping is provided which is in particular fixedly set. Such a high-speed damper valve serves in particular to generate an adequate damping effect in the case of heavy impacts or the like while in normal riding operation the high-speed damper valve is, closed and does not show any effect. 
         [0031]    Preferably, the damper chamber is configured as an internal chamber that is enclosed by an external chamber at least in part. 
         [0032]    The damper chamber is preferably configured as a high pressure chamber while the control section comprises a low pressure chamber or a compensation chamber. The high pressure region is separated from the low pressure region by means of the damper valves. 
         [0033]    Preferably the control section is provided with a riser for the compression stage and a riser for the rebound stage such that both in the compression stage and in the rebound stage the damping fluid provided in particular as an oil rises up to the damper valves from where it is dampened and conveyed further into the low pressure chamber. 
         [0034]    The damper system according to the invention in particular for a stanchion tube of a suspension fork of a bicycle comprises a movable piston which divides a damper chamber into a first and a second chamber. Furthermore, damper valves for adjusting the rebound damping and for adjusting compression damping are provided. The damper system is suitable to be inserted in a stanchion tube of a suspension fork. The damper system comprises at least one shut-off valve for adjusting a lockout in the rebound stage and at least one shut-off valve for adjusting a lockout in the compression stage. Furthermore, a joint adjusting element is provided with which to activate the locking of the rebound stage or the lockout in the rebound stage and locking of the compression stage or lockout in the compression stage. 
         [0035]    The damper system according to the invention also has many advantages. One considerable advantage of the damper system according to the invention is the flexibility in application. The damper system according to the invention allows to lock both the rebound stage and the compression stage through simple operation of one joint adjusting element. This allows adjustment to any desired height of the suspension fork such that the suspension fork can be fixed in the desired compressed position since with locking activated in the compression stage and locking activated in the rebound stage a compressing movement or decompressing movement of the suspension fork is not possible in principle. 
         [0036]    Preferably, the joint adjusting element is provided at a control section above the damper chamber to enable the rider of a thus equipped bicycle operation during a ride. Then, to operate the joint adjusting element the rider only needs to bend down to the adjusting element which is advantageously disposed in an upper region of the stanchion tubes of the suspension fork to operate the joint adjusting element and to set the desired position. The adjusting element may be provided to be remotely controlled and it may be connected with an adjusting element or an adjusting lever at the handlebar through a control cable or a Bowden cable or an electrical connection. 
         [0037]    In all the configurations the suspension fork is preferably configured in right-side-up structure in which the stanchion tubes affixed in the fork bridge of the suspension fork plunge into the larger-diameter slider tubes. Employing with other suspension forks according to a different construction principle is possible as well. 
         [0038]    In all the configurations and more specific embodiments the slider tubes are preferably provided for a sliding contact with the stanchion tubes of the suspension fork. Preferably, the stanchion tubes are supported in the slider tubes by means of slide bearings. 
         [0039]    Preferably, the lower end of at least one slider tube is provided with a dropout which is in particular provided to receive a wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    Further advantages and applications of the present invention ensue from the description of exemplary embodiments which will now be discussed with reference to the enclosed figures. 
           [0041]      FIG. 1  is a front view of a suspension fork according to the invention; 
           [0042]      FIG. 2  is a cut side view along A-A of the suspension fork in  FIG. 1 ; 
           [0043]      FIG. 3  is an enlarged, cut side view of the suspension fork in the compression stage; 
           [0044]      FIG. 4  is a cut side view of the suspension fork in the rebound stage; 
           [0045]      FIG. 5  is an enlarged view of the control section of the damper system of the suspension fork in  FIG. 3  in the compression stage; 
           [0046]      FIG. 6  is an enlarged view of the control section of the damper system of the suspension fork in  FIG. 4  in the rebound stage; 
           [0047]      FIG. 7  is the control section of the damper system of the suspension fork in  FIG. 1  with the adjusting lever in the first shift stage; 
           [0048]      FIG. 8  is the control section of the damper system of the suspension fork in  FIG. 1  with the adjusting lever in the second shift stage; 
           [0049]      FIG. 9  is an enlarged cross-section of a stanchion tube in the upper region; 
           [0050]      FIG. 10  is an enlarged cross-section of a stanchion tube in the region of the overflow aperture; 
           [0051]      FIG. 11  is the suspension fork of  FIG. 1  with the rebound stage locked in compressing; 
           [0052]      FIG. 12  is the suspension fork of  FIG. 1  with the rebound stage locked after intense compression; 
           [0053]      FIG. 13  is the suspension fork of  FIG. 1  with the rebound stage locked and subsequent slow decompression; 
           [0054]      FIG. 14  is an enlarged illustration of a cross-section of the control section of another suspension fork; 
           [0055]      FIG. 15  is another cross-section of the control section of the suspension fork according to  FIG. 14 ; and 
           [0056]      FIG. 16  is an enlarged cross-section of the suspension fork according to  FIG. 14  with the movable piston. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    In  FIGS. 1 to 13 , a first embodiment of the suspension fork  1  according to the invention is illustrated in views some of which are highly schematic. For better clarity and to better explain the function, some parts and components have been omitted. 
         [0058]    The suspension fork  1  illustrated in  FIG. 1  in a front view for a bicycle, presently not shown, comprises in its upper region a fork column  26  that is centrally attached to a connector  7  configured as a fork crown  27  to rotatably attach the fork to the bicycle frame. 
         [0059]    The two ends of the fork crown  27  have stanchion tubes  2  and  3  affixed to the fork crown  27 . A damper system  8  is disposed in the stanchion tube  2  and a suspension system  50  is provided in the stanchion tube  3 . It is also conceivable to incorporate the damper system  8  and also the suspension system  50  in a stanchion tube  2  or  3 . By means of the damper system  8  and the suspension system  50  the suspension fork  1  is provided with the desired springing and damping properties. 
         [0060]    A slider tube unit is displaceably provided at the stanchion tubes  2  and  3 , comprising slider tubes  4  and  5  connected with one another through at least one connecting bracket  56 . The slider tube unit may consist of several component parts but it may as well be manufactured integrally. 
         [0061]    The wheel receiving space  6  is provided between the pair of slider tubes  4  and  5  or between the stanchion tubes  2  and  3 . A wheel, presently not shown, may be attached to the dropouts  18  and  19  of the slider tubes  4  and  5  at the lower end  17  of the suspension fork  1 . 
         [0062]    At the upper end  16  a damper system  8  is incorporated in the stanchion tube  2 , as can be taken in particular from  FIG. 2 . 
         [0063]    The damper system  8  comprises a damper chamber  10  divided into an upper, first chamber  11  and a lower, second chamber  12  by means of a movable piston  9 . Above the damper chamber  10  a control section  15  is provided which concurrently forms the top end of the damper chamber  10 . The movable piston  9  is presently configured as a closed pump plunger. A flow through the movable piston  9  is not possible as a rule. When the piston is moved, external return flow must occur from the upper or first damper chamber  11  to the lower or second damper chamber  12 . 
         [0064]    While the damper chamber  10  with the first chamber  11  and the second chamber  12  is configured as a high pressure chamber  29 , the control section  15  is provided with a low pressure chamber  32 . 
         [0065]    A damping device  57  for rebound damping and a damping device  58  for compression damping are provided in the control section  15 . Presently the damping device  57  is provided as an adjustable damper valve  13  for adjusting the rebound stage damping and the damping device  58 , as an adjustable damper valve  14  for adjusting the compression stage damping. Furthermore, a shut-off valve  24  for the rebound stage, a shut-off valve  25  for the compression stage, and high-speed damper valves  22 ,  23  for the rebound stage and the compression stage and a blow-off valve  48  are provided. 
         [0066]    At the upper end of the first chamber  11  of the damper chamber a check valve  51  is provided which by means of a spring not shown in any detail is preloaded in a closed position in which the check valve  51  closes the direct flow connection with the low pressure chamber  32 . The check valve  51  opens as the first chamber has a relative negative pressure in the rebound stage (see  FIG. 6 ). 
         [0067]    A check valve  52  is provided which is preloaded in the closed position by means of a spring that is again not shown in detail. The check valve  52  opens as the second chamber  12  has a relative negative pressure in the compression stage (see  FIG. 5 ) and the damping fluid is sucked from the low pressure chamber  32  through the return channel  35  and the external chamber  31  into the second chamber  12 . 
         [0068]    In the rebound stage, the damping medium supplied to the riser  34  from the return channel  35  is introduced into the low pressure chamber  32  through the damper valve  13 . In the case of the compression stage, the damping medium introduced into the duct riser  33  from the first chamber  11  is introduced into the low pressure chamber  32  through the damper valve  14 . Then in the compression stage, the damping fluid enters from the first chamber  11 , which forms part of the internal chamber  30 , through the riser  33  into the control section  15 . Depending on the position of the damper valve  14  for adjusting compression damping and after application of a load, the damping fluid is introduced through the damper valve  14  and/or through the high-speed damper valve  23  into the low pressure chamber  32 . 
         [0069]    In the case of the rebound stage, the damping fluid enters from the second chamber  12  in the lower region of the damper system  8  into the external chamber  31  which is configured as a high pressure chamber and which is confined in the lower region  36  of the second chamber  12  by the external wall of the stanchion tube  2  and by a center tube  37  which radially encloses the stanchion tube  2  in the lower region  36  of the second chamber  12 . In this way a thermal insulation is achieved from the slider tube  4  which encloses the stanchion tube  2  in the lower region  36  of the second chamber  12  so as to largely prevent the slider tube  4  from heating in the lower region. 
         [0070]    In relation to the loads occurring, the movable piston  9  slides upwardly and downwardly inside the damper chamber  10  wherein radially outwardly sealing against the internal chamber  30  occurs through a seal  49 . 
         [0071]    The damper valves  13  and  14  in the present embodiment are disposed displaceably via adjusting elements  21 . The adjusting elements  21  may be configured as screw heads  28  wherein rotating the adjusting element  21  inserts the respective damper valve  13  or  14  further into the top end wall of the control section  15 . In this way, slots or radial bores  54  and/or  55  through which the damping oil is directed in the compression stage or the rebound stage, are widened or narrowed. In this way, via rotational movement of the adjusting elements  21  of the damper valves  13  and  14 , an efficient adjustment of the damping effect of the rebound stage and the compression stage is possible separate from one another. This adjustment of the damping effect in particular occurs for normal operation in which the suspension fork is adjusted for damping small to medium or else heavy impacts. 
         [0072]    To ensure damping including in the case of particularly heavy impacts, the high-speed damper valves  22  and  23  are provided for the rebound stage or the compression stage respectively. Although the high-speed damper valves  22  and  23  are as a rule not provided to be adjustable, this is possible as well. 
         [0073]    In the present embodiment preloading devices are provided which are for example configured as coil springs so as to preload the respective high-speed damper valves  22  and  23  in the closed position. Now, as particularly large impacts occur the pressure in the damper chamber rises correspondingly such that the force of the respective preloading devices is overcome and the respective high-speed damper valve  22  or  23  opens. This will cause the valves to open in the case of sufficiently forceful loads. 
         [0074]      FIG. 3  shows compressing in the compression stage while  FIG. 5  shows the positions of each of the valves in enlarged illustration.  FIG. 4  shows decompressing in the rebound stage while  FIG. 6  shows enlarged illustrations of the valve positions. 
         [0075]    It can clearly be seen in  FIGS. 3 to 6  that both the shut-off valves  24  and  25  are open while the damper valves  13  and  14  are illustrated open or closed, depending on the operating condition. 
         [0076]    As can in particular be taken from the illustration in  FIG. 3 , an overflow aperture  45  is located at the distance  46  from the lower end of the damper chamber  10  so as to allow the damping fluid to exit from the second chamber  12  even if the shut-off valve  24  for the rebound stage is closed until the piston  9  closes the overflow aperture  45 , presently from above. 
         [0077]    The shut-off valves  24  and  25  for the rebound stage and the compression stage serve to selectively prohibit damping in the rebound stage or in the compression stage. Damping may be prohibited by activating either of the valves such that the flow passage either for the rebound stage or the compression stage closes. 
         [0078]    It is a considerable advantage of the illustrated embodiment that one single adjusting lever  40  is provided as the adjusting element  21  with which to intentionally and selectively jointly activate both the shut-off valve  24  of the rebound stage and the shut-off valve  25  of the compression stage. 
         [0079]    To this end the adjusting lever  40  is pivotally disposed at the upper end  16  of the control section  15  such that the adjusting lever  40  presently projects from the upper end of the stanchion tube  2  and can be actuated by the rider as the operator while riding. All the rider needs to do is move one hand down to the fork crown  17  of the fork  1  and then by way of rotationally moving the adjusting lever  40  he can shift between presently three or even up to four shift stages provided. In a preferred configuration the adjusting lever  40  may be configured as a remotely controlled adjusting element actuated e.g. by a control mechanism at the handlebar. 
         [0080]    In a first setting  41  of the adjusting lever  40  the situation illustrated in  FIG. 5  is achieved in which both the shut-off valve  24  of the rebound stage and the shut-off valve  25  of the compression stage are not activated so as to allow free flow through the valves  24  and  25 . This is the standard operating condition of the suspension fork  1  in which both a rebound damping and a compression damping and compression and decompression are possible. 
         [0081]    By way of rotational movement of the adjusting lever  40  from the position  41  to the second rotational position  42  as illustrated in  FIG. 7 , the shut-off valve  24  of the rebound stage is activated and thus closed such that in the rebound stage flow-through is substantially disabled. In the compression stage the shut-off valve  25  is still open. This means that compression is still possible while subsequent rebound is prohibited. Such a rotational position  42  of the adjusting lever  40  makes sense for example when the rider climbs a steep incline and wishes to reduce the inclination angle of the bicycle. By means of the front wheel fork compressing, its effective height decreases so that a safe and comfortable riding position is achieved. After activation of the pivot position  42  by the adjusting lever  40  being rotated, every impact and every compression causes the front wheel fork  1  to lower until a provided setting is reached. 
         [0082]    By way of rotating the adjusting lever  40  further into the third shift position  43  illustrated in  FIG. 8  one achieves that not only the shut-off valve  24  for the rebound stage but also the shut-off valve  25  for the compression stage is closed. Adjusting the adjusting lever  40  in this way is possible at any time. In this way both decompression and compression of the fork is prohibited. The suspension fork  1  practically behaves as if no suspension and damper system were present. Only in the case of particularly heavy impacts the blow-off valve  48  can be activated, allowing flow-through so as to limit the maximum pressure occurring in the system and to prevent the damper system  10  of the suspension fork from being damaged or from breaking, for example if the rider jumps with his bicycle while the adjusting lever is in the third shift stage  43 . 
         [0083]    It may further be possible to shift the adjusting lever  40  to a fourth shift stage  44  in which the shut-off valve for the compression stage is closed while the shut-off valve  24  for the rebound stage is open. In this way decompression of the spring is allowed while compression is prohibited. 
         [0084]    The suspension fork  1  furthermore comprises the overflow valve  45  indicated above which is provided at a distance  46  from the lower end of the first chamber  12 . By means of the overflow aperture  45  the suspension fork  1  is prevented from compressing completely if the shut-off valve  24  of the rebound stage is activated. 
         [0085]    A connecting duct  60  is provided in which at least one flow damper  63  is provided. The connecting duct  60  serves to allow the suspension fork to slowly, automatically rebound back to a specific measure when the shut-off valve  24  of the rebound stage is activated after heavy compressions. 
         [0086]    To this end the connecting duct  60  provides a flow connection for the damping fluid between the second chamber  12  and the first chamber  11  as the stanchion tube  2  and the slider tube  4  cooperating therewith have compressed by more than a specified distance  46 . In this way, in the case of forceful compression and with the shut-off valve  24  of the rebound stage activated, slow decompression is allowed up to a damper position  68  as defined by the predetermined distance  46 . 
         [0087]    The configuration of the overflow valve or the overflow aperture  45  is illustrated enlarged in the  FIGS. 9 and 10 . In the range between approximately 20 and 50% of the compression travel at least one overflow aperture  45  is provided at the damper chamber  10 . The overflow aperture  45  is located at the distance  46  from the bottom while the maximum stroke corresponds to the length  47 . Presently, the at least one overflow aperture  45  is connected with the aperture  61  via the duct formed as an annular duct  62  and presently opens into the riser  33 . In this way damping fluid can immediately flow from the chamber  12  into the riser  33  and thus return into the chamber  11 . The damping fluid can pass from the chamber  12  via the overflow aperture  45  into the duct  60  and further through the aperture  61  into the riser  33  and further into the first chamber  11  such that the suspension fork rebounds until the piston closes the overflow aperture  45  again. 
         [0088]    The flow damper  63  is presently formed in particular by the overflow aperture  45  or by the overflow apertures  45 , if several are present. The flow cross-section  64  of the flow damper  63  is formed by the clear passage area of the overflow aperture  45  (or by the sum of the areas of each of the overflow apertures  45 ). At any rate, the flow cross-section  64  is presently substantially smaller than half the maximum flow cross-section of the damping device  58  or the damper valve  14  for the compression stage. 
         [0089]    The ratio of the flow cross-section  64  of the flow damper  63  to the maximum flow cross-section of the damping device  58  for the compression stage is in particular smaller than 1:3 and preferably smaller than 1:5 and particularly preferably smaller than 1:8. Values of 1:10 or 1:20 and in particular 1:30 are conceivable and preferred. The area is in particular dimensioned such that the connecting duct  60  when open only slightly influences the damping reaction of the suspension fork. 
         [0090]    The same preferably applies to the ratio of the flow cross-section  64  of the flow damper  63  to the maximum flow cross-section of the damping device  50  for the rebound stage. 
         [0091]    The annular gap  62  is confined by an internal tube  65  and a center tube  66  both of which are positioned concentrically inside the stanchion tube. 
         [0092]    In other configurations the connecting duct can be shut off e.g. via a controllable valve. 
         [0093]    In other configurations the duct  60  may open immediately into the low pressure chamber  32  through an aperture  61  (variant not illustrated). Thus, a suspension fork can be adjusted to different operational modes. The suspension fork may be adjusted to be entirely rigid. The suspension fork may be compressed a specific amount e.g. for riding up-hill. 
         [0094]    The function and mode of operation of the overflow valve  45  will now be explained with reference to  FIGS. 11 to 13 . 
         [0095]    In the illustration of  FIG. 11  the suspension fork  1  is in the rebound state with the shut-off valve  24  of the rebound stage activated to allow the suspension fork  1  to compress while rebound is substantially prohibited. 
         [0096]    After activating the shut-off valve  24  by displacing the adjusting lever  40  to the second shift stage  42  the riser  34  is closed for the rebound stage. The impacts occurring during the ride cause the suspension fork  1  to lower until the suspension fork has reached for example the position shown in  FIG. 13  in which the piston  9  is compressed down to the overflow aperture  45 . 
         [0097]    Now when another heavy impact acts on the suspension fork  1  in this position, the suspension fork is compressed further beyond the overflow aperture  45  (see  FIG. 12 ). Thus the overflow aperture  45  is opened such that the locking action of the shut-off valve  24  is bypassed. The connecting duct  60  connects the second chamber  12  with the first chamber  11  and the suspension fork is automatically slowly lowered. The exchange of the damping fluid occurs slowly because the flow cross-section  64  of the overflow aperture  45  serving as the flow damper  63  is small. 
         [0098]    Owing to the overflow aperture  45  the suspension fork  1  can rebound back until the condition shown in  FIG. 13  is achieved in which the overflow aperture  45  is closed again. 
         [0099]    On the whole a system is provided by means of the overflow aperture  45 , the activated shut-off valve  24  notwithstanding so as to limit the suspension travel even if the shut-off valve  24  of the rebound stage is activated. By way of disposing the overflow aperture  45  the desired suspension travel can be adjusted. 
         [0100]    In this way a function is provided which in up-hill rides provides the required compression while on the other hand a small damping function continues to be available. 
         [0101]    With several adjustable or shiftable overflow apertures  45  provided at different heights, the suspension travel still available with the shut-off valve  24  activated can be adjusted correspondingly. 
         [0102]    The  FIGS. 14 to 16  show cross-sections of another embodiment of a suspension fork  1  according to the invention. Like or similar parts are provided with the same reference numerals. The damper system  8  in turn is inserted in a stanchion tube  2  or  3  of a suspension fork  1 , as shown in  FIG. 1 . 
         [0103]    Unlike the preceding embodiment, the embodiment according to  FIGS. 14 to 16  provides for the damper valve  13  to be a low-speed damper valve for the rebound stage at the top end of the damper chamber  10 . The damper valve  14  as a low-speed damper valve for the compression stage is likewise disposed at the top end of the damper chamber  10 . The valves separate the high pressure region from the low pressure region. The control section  15  virtually extends from the upper end of the first chamber  11  to the upper end  16  of the stanchion tube  2 . 
         [0104]    The damper valves  13  (low-speed) for the rebound stage and  14  (low-speed) for the compression stage are connected with the upper end  16  through corresponding control elements or control pins and they are adjustable by way of actuating the adjusting element  40 . 
         [0105]    In  FIG. 14 , it can be seen that the control pin  73  acts on the shut-off valve  24  for the rebound stage such that lockout may be activated as needed and rebound damping may be locked. A control pin  75  acts on the shut-off valve  25  for the compression stage and it may selectively lock compression damping. In the case of particularly forceful shocks the blow-off valve  48  opens if the shocks generate a force exceeding the interior force of the spring  74  of the blow-off valve  48 . 
         [0106]    The blow-off valve  48  is sealed by means of seals  77  both relative to the control pin  76  and to the external wall. 
         [0107]    The high-speed damper valve  23  is presently connected in parallel to the low-speed damper valve  14 . 
         [0108]    Above the shut-off valves  24  and  25  the oil compensation chamber  72  is separated from a gas volume  79  by means of a partition wall. The partition wall is presently configured as a rubber hose  70 , ensuring reliable separation of the oil from the gas volume. The gas volume  79  is under excess pressure of typically between 1 and 5 bar. The movable piston  9  is presently configured as an impermeable pump plunger. When the movable piston  9  plunges, the volume available to the oil is reduced. In this way the gas volume  79  compresses by means of the flexible rubber hose  70  and the compensation chamber  72  expands correspondingly. 
         [0109]    The O-ring  71  covers a bore. The O-ring  71  together with the bore serves as a one-way valve and serves for filling up the suspension fork with gas after mounting. The one-way valve opens as the internal pressure expands the O-ring far enough for gas to exit through the gap generated. 
         [0110]      FIG. 15  shows another cross-section of the control section  15  wherein  FIG. 15  shows a cross-section approximately transverse to the cross-section according to  FIG. 14 . 
         [0111]    One can see the damper valve  13  as a low-speed control valve for the rebound stage. By way of longitudinal adjustment the regulating gap  69  is regulated and thus the flow resistance is adjusted. 
         [0112]      FIG. 16  shows a cross-section of the region of the piston in the lower region of the damper chamber, where as in the preceding embodiment the overflow aperture  45  is provided. 
         [0113]    The piston rod  20  is sealed by way of a seal  77  against the damper chamber  10 . At the upper end of the piston rod  20  the movable piston  9  is provided that is configured as a pump plunger and that separates the first chamber  11  from the second chamber  12 . 
         [0114]    At its bottom, the second chamber  12  makes a transition to the interspace  38  connected therewith. The second chamber  12  or the low-pressure region is limited externally by the center tube  37  that is sealed externally by means of a seal  77  towards the stanchion tube. At its upper end, the interspace  38  is radially outwardly connected with the external chamber  31  through at least one aperture  78 . The second chamber  12  together with the interspace  38  and the external chamber form the rebound stage chamber. 
         [0115]    Positioned radially within the external chamber  31  the center tube  66  is provided in which the inner tube  65  is positioned concentrically. Between the inner tube  65  and the center tube  66  a duct  60  is provided. From the duct  60  an aperture  61  opens into the first chamber  11  in an upper region and an aperture  45  into the damper chamber  10 , in a lower region. In this way the duct  60  acts as a bypass between the first chamber  11  and the second chamber  12  when the movable piston  9  is located between the apertures  45  and  61 . In this way, compensation is possible even in the case of a locked damping. Compensation occurs slowly since the flow cross-sections of the apertures are intentionally small. 
         [0116]    To still further reduce the flow-through quantities through the overflow apertures  45  and  61 , O-rings  71  may be provided across the overflow apertures  45  and  61 . In this way, it is achieved that a specific pressure must first be overcome which further slows down the flow and thus inhibits normal function as little as possible. It has been shown that the overflow apertures  45  and  61  ought to be very small. And even in the case of small apertures it makes sense to further reduce flow-through. 
         [0117]    Another considerable advantage of the overflow apertures  45  and  61  and the bypass thus provided is that independently of the weight of the rider the same position will always be adjusted even in the case of a locked rebound stage. This position is independent of the acting forces and it is defined by the position of the bore. This is very advantageous since in this way the same position is set for every rider which is very advantageous in particular in steep uphill rides. 
         [0118]    The function will now be described briefly: In the compression stage, i.e. during compression and with the shut-off valves  24  and  25  opened. 
         [0119]    Following a shock, the movable piston  9  configured as a pump plunger moves upwardly and the pressure in the first chamber  11  above the piston  9  increases. Then the oil will flow upwardly through the damper valve  14  (compression stage valve low-speed). 
         [0120]    The damper valve  23  is preloaded by a spring such that in the case of small loads a shim seals the damper valve  23 . From a specific load or from a corresponding excess pressure onwards the high-speed damper valve  23  of the compression stage opens additionally such that the damper valves  14  and  23  are opened in parallel. The oil flows upwardly into the oil compensation chamber  72  at the upper end of the stanchion tube. The oil compensation chamber  72  configured as an annular chamber is formed between the stanchion tube wall and the flexible rubber hose  70 . The rubber hose  70  compresses by way of the oil flowing into the oil compensation chamber  72 . In the interior of the rubber hose  70  a gas volume  79  is present. The gas volume  79  is presently filled with air and in the present case under a pressure of e.g. 3-4 bar. In this way any cavitation in the flowing oil is avoided. By way of the rubber hose and the gas volume the volume of the piston rod is compensated. And, for thermal expansion of the oil a suitable reservoir is provided. 
         [0121]    During compressing the pressure concurrently decreases in the second chamber  12  below the movable piston  9 . At its bottom the second chamber is in flow connection with the interspace  38  and the external chamber  31 , from where oil is now drawn. The external chamber  31  abuts the control section  15 . A return flow valve opens there and oil flows out of the oil compensation chamber  72  from above. 
         [0122]    In rebounding in the rebound stage the movable piston  9  moves downwardly and excess pressure forms in the lower, second chamber  12  and thus also in the external chamber  31  while negative pressure forms in the first chamber  11  above the piston  9 . 
         [0123]    By way of the negative pressure in the first chamber  11  at least one check valve positioned at the upper end opens, and oil is drawn from above from the oil compensation chamber  72 . 
         [0124]    On the whole the suspension fork  1  according to the invention provides a system which allows high heat dissipation in the upper region of the stanchion tubes  2 ,  3  wherein all the operating elements  21 ,  40  can be flexibly arranged in an upper region  16  of the stanchion tubes  2  and  3 . 
         [0125]    In all the embodiments at least one shut-off valve  24  or  25  and/or at least one damper valve  13  or  14  may be actuated or activated electrically or magnetically. A remotely controlled construction is in particular possible and preferred. Operating is e.g. possible from the handlebar. A mechanical remote control is also preferred. 
         [0126]    Furthermore the damper valves  13 ,  14 ,  22 - 25  are also located in the upper region  16  of the stanchion tubes  2  or  3  and via a shared adjusting lever  40  provided at the fork crown  27  or at the stanchion tube  2 ,  3 , both a rebound stage lockout (locked rebound stage shut-off valve) and a compression stage lockout (locked compression stage shut-off valve) may be set such that the fork  1  is rigid both in the compressing direction and in the decompressing direction. At the same time a damping function can be ensured via an overflow valve  45  even with the rebound stage lockout activated.