Abstract:
A piston/cylinder unit, in particular a gas spring, includes a valve device for the operational motion of a piston rod. The valve device is activatable by an activation device, the activation device being connected near an actuation device and being connected to a load contact device, which influences the function of the valve device. The load contact device connects the actuation device to the valve device for the purpose of changing the adjustability of the valve device when the gas spring is loaded.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an activation device for a piston/cylinder unit, in particular for a gas spring, whose movement can be selectively inhibited and includes a valve device for operational motion of a piston rod and an activation device for operating the valve device. 
     2. Description of the Prior Art 
     Gas springs whose movement can be selectively inhibited are employed, for example, in chairs which have a seat back which is spring-supported and can be rigidly held by the selective inhibiting function of the gas spring. A chair user does not, however, continuously adopt the same posture on the chair. The seat back position can be very easily matched to the instantaneous seating position by the activation device. The user may also, for example, lean forward so that the seat back has no contact with the back of the user. If the activation device for the gas spring on the seat back is actuated while the user is in this position, the seat back is accelerated by the gas spring in the direction of the user&#39;s back and impinges on it. This operational behavior is undesirable. German reference DE 69 35 911 U1 describes a gas spring which has a divided activation push-rod, a spring being arranged between the two activation push-rod sections. Slower opening of the blocking valve within the gas spring is achieved using the spring. 
     A similar activation means is described in German reference DE 36 15 688 A1 in which a valve cross section of the blocking valve changes over the stroke path of the activation push-rod. The throttling associated with this valve only permits the piston rod to extend slowly at the beginning of the stroke path of the activation push-rod and then increasingly more rapidly toward the end of the activation push-rod stroke length. Although the problem of undesireable contact with the seat back is diminished by both of these prior art types of gas springs, it is by no means reliably prevented. 
     GB 2 304 036 A1 (GB &#39;036) relates to an activation device which has two switching inputs. The activation push-rod can, on the one hand, be activated by means of a Bowden cable. In addition, the seat support is in connection with the activation device such that when the seat support is unloaded, the gas spring is always in the unlocked operating function is always adopted on the gas spring independently of the switching condition of the Bowden cable. An activation appliance, which acts directly on the activation push-rod and which is embodied as a rocker arm is used for activating the Bowden cable. An essential feature is that the seat panel is required to pivot for recording the loading condition. However, this imposes a limitation to the chair design. Comfortable chairs often feature a seat inclination adjustment. Such a seat inclination adjustment would have a substantial influence on the function of the activation device of GB &#39;036. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a piston/cylinder unit, in particular a gas spring, having a braked operating motion independent of stroke. 
     According to the present invention, the object is achieved by a loaded gas spring having a load contact device connecting an actuation device to the valve device of the gas spring piston for the purpose of changing the adjustability of the valve device. When using a chair, the load contact device is associated with the advantage—for the user of the chair—that when the seat back is not in contact with his back, the inhibited movement position of the gas spring cannot be canceled by a switching movement on the actuation device. If, however, the seat back is in contact with the user&#39;s back, then the load contact device permits a comfortable seat back adjustment using the actuation device. The seat back does not strike the user because it is already in contact with his back. 
     The load contact device may include a slide which can move relative to the gas spring. The slide is in effective connection with the actuation device at a fixed location. When the seat back is loaded by the user, the slide moves the actuation device into a position from which an effective actuation motion can take place. 
     To continually ensure a defined operating position of the load contact device, the slide is preloaded by a spring in the direction of a disengaged position of the load contact device. 
     It should, as far as possible, be possible to combine the load contact device according to the invention with a standard gas spring. For this purpose, an activation push-rod for the valve device is divided in two parts in the axial direction. A first part of the activation push-rod is contained in the gas spring as a series production item. A second part, which has the approximate axial length of the load contact device, can then be used as an adapter. 
     To obtain increased design freedom in the choice of the spring for the load contact device, the load contact device has a spring support, which is firmly connected axially to the gas spring. As an alternative, the spring may also be arranged to engage on an end surface of the gas spring. 
     The spring support may thus be formed by a threaded sleeve. The threaded sleeve permits adaptation of the position of the load contact device to compensate for possible manufacturing tolerances. 
     To ensure that the gas spring has a reliable fastening to the load contact device, an axial stop may be used to limit the displacement path of the load contact device. In this arrangement, the axial stop contacts the spring support. 
     The slide, an end of the slide for supporting the spring urgency and the axial stop for receiving the other end of the spring form a casing of the load contact device, in which the spring is enclosed. This allows the load contact device to be manufactured as a structural unit independently of the technical application and the gas spring can be manufactured as a separate sub-assembly. 
     In addition, the end of the slide forms a further axial stop acting in a direction opposite to that of the first axial stop, so that the operational movement of the slide is limited in both directions and the spring is not necessarily preloaded to provide the blocking function. 
     In a particularly simple embodiment, the spring is supported on the cylinder. The major advantages of this solution is that it is possible to dispense with a separate casing. Furthermore, the use of the load contact device according to this embodiment requires practically no loss of the stroke of the conventional piston/cylinder unit. 
     The spring support may be fastened to the cylinder, the spring being supported on the unit composed of the slide and the activation device. 
     Furthermore, the slide may be supported on the piston rod. The piston rod features a very high-quality surface so that good guidance is provided. It is, furthermore, possible to dispense with a fastening thread for the load contact device. 
     Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein like reference characters denote similar elements throughout the several views: 
     FIG. 1 is a partial cutaway side view of a chair including a piston/cylinder unit according to an embodiment of the present invention; 
     FIG. 2 is a sectional view of a gas spring with a load contact device as a sub-assembly of the piston/cylinder unit from FIG. 1; 
     FIG. 3 is a sectional view of a load contact device and activation device of a gas spring according to another embodiment of the present invention; 
     FIG. 4 is a sectional view of the load contact device and activation device of a gas spring of FIG. 3 in the loaded position; and 
     FIG. 5 is a detailed sectional view of the activation device of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a chair  1  having a seat carrier  3  and a seat back  5  supported on the sear carrier  3  so that the seat back  5  is pivotable about a bearing  7 . A piston/cylinder unit  9  designed as a gas spring is functionally arranged between the seat back  5  and the seat carrier  3 . By means of an activation device  11  including an actuating lever  12 , the gas spring  9  may be switched into an inhibited movement position or an enabled movement position. 
     FIG. 2 shows, on an enlarged scale, the gas spring  9  with the activation device  11  as a sub-assembly. A piston rod  15  is arranged so that it can be moved axially within a cylinder  13  filled with a pressurized gas. A separating piston  17  which includes a valve device  19 , is arranged at the end of the piston rod  15  located within the cylinder. The valve device  19  influences a flow connection  21  between working spaces  23 ,  25  of the cylinder which are separated by the piston. A valve push-rod  27  of the valve device  19  is actuatable by an activation push-rod  29  within the hollow piston rod  15  by the outer end of the piston rod. 
     When the valve device  19  is in the inhibited position, the flow connection  21  is closed and the piston rod motion is blocked in both axial directions whereas, when the flow connection  21  is open, a pressure force in the extension direction acts on the piston rod  15 . 
     The cylinder  13  and the activation device  11  each have a connection element  31 ,  33  for fastening the gas spring between the seat back  5  and the seat support  3 . 
     The activation device  11  arranged on the piston rod  15  also includes a load contact device  37 . The load contact device has a slide  39  which is axially moveable relative to the piston rod  15 . A spring  43  is supported on a spring support  45  and preloads the slide  39  via an end  41  of the slide. The spring support  45  is part of a threaded sleeve  47  which is fastened to the piston rod  15 . An axial stop  49  engages behind the spring support  45  so that the maximum displacement movement of the slide  39  is determined by the maximum possible distance between the end  41  and an end surface  51  of the piston rod  15 . The slide  39  including the end  41  and the axial stop  49  form a casing in which the spring  43  is enclosed, the casing representing a sub-assembly which can be manufactured independently of the gas spring  9 . 
     FIG. 2 shows the gas spring  9  in the unloaded position in which there is, because of the spring force of the spring  43 , a distance between a pressure surface  53  of the actuation device  35  and an end surface  53  of the activation push-rod  29 . The distance between the two parts is greater than or equal to the maximum distance between the end  41  and the end surface  51  of the piston rod  15 . The load contact device  37  is in a disengaged position. A pivot bearing  57  of the actuation device  35  is arranged to have a fixed axial location relative to the load contact device  37 , namely the end  41  and the slide  39 , so that the actuation device  35  moves with the load contact device during a displacement movement of the load contact device  37 . If the actuation device  35  is moved in the direction of the activation push-rod  29 , a contact with the activation push-rod  29  may be produced in any event. However, a further actuation movement of the actuation device  35  is prevented by a stop  59  (only represented in principle) in the unloaded position of the load contact device. As a result, the valve device  19  within the gas spring  9  cannot be switched over when the gas spring is unloaded. 
     When the gas spring is loaded such as, for example, when a person leans on the seat back, the connection element  33 , together with the load contact device  37  and the actuation device  35 , is displaced in the direction of the activation push-rod  29 . This displacement causes the end  41  of the slide  39  in the load contact device  37  to contact the end surface  51  of the piston rod  15 . The spring  43  does not, in any case, have to support the load on the seat back  5 . Rather is is only required to produce a disengagement force to again disengage the load contact device upon unloading of the gas spring. If the actuation device  35  is activated while the gas spring is loaded, a small idle path, which compensates for manufacturing tolerances, can under certain circumstances be overcome but, otherwise, the valve device  27  is moved into a disengagement setting by means of the actuation device  35  and the activation push-rod  19  in contact with it. The associated extension force on the piston rod  15  does not cause any impact by the seat back on the person because contact is already present. 
     The load contact device  37  does not necessarily have to be arranged on the piston rod  15  but may also act on the cylinder  13  if, for example, the valve device  27  is embodied in the region of the cylinder-end connection element  31 . 
     The activation push-rod  29  may also comprise two parts, as is indicated by the dashed line in FIG. 2. A standard gas spring may be used without modification with a further length section of the activation push-rod used with the load contact device. 
     FIGS. 3-5 depict a further embodiment of the invention in which the slide  39  of the load contact device  37 , see FIG. 5, is almost completely arranged within the activation device  11  and is directly supported on the piston rod  15 . One end of the spring  43  is supported on a spring plate  61  arranged on the activation device and the other end of spring  43  is supported on the spring support  45  arranged on the cylinder  13 . Two axial stops  63 ,  65  are fastened as securing rings on the piston rod  15  to limit the displacement path of the slide  39 . The end  67  of the activation device  11  may be supported on the end surface  51  of the piston rod, which may also provide the axial stop. 
     During assembly, the slide  39  is fed onto the piston rod  15 . The axial stop  65  is then assembled on the piston rod. In the next step, the slide  39  is pushed as far as the axial stop  65  and the other axial stop  63  is fastened to the piston rod. Finally, the activation device  11  is pushed onto the slide  39 . A press connection or threaded connection may be used to effect the connection between the activation device and the slide. 
     In FIG. 3, the piston/cylinder unit is shown unloaded so that the spring  43  preloads the activation device  11 , together with the slide  39 , onto the axial stop  65 . In this position, the actuation device  35  is displaced so far firm the activation push-rod  29  that the actuation device can not be activated in this position. 
     FIG. 4 includes force arrows symbolizing a pressure loading on the piston/cylinder unit when, for example, a person loads the seat back  5 , see FIG.  1 . The external forces displace the activation device  11 , together with the slide  39 , against the force of the spring  43  until the activation device comes into contact, by means of the slide, with the axial stop  63 . In this operating position of the activation device  11 , the activation push-rod  29  can be activated by the actuation device  35  to enable movement of the gas spring. 
     Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.