Patent Publication Number: US-2009236783-A1

Title: Gas Spring

Description:
The invention is directed to a gas spring with a center longitudinal axis and a closed first end, a cylinder which is filled with a fluid under pressure, a piston which is displaceably arranged in the cylinder and which divides the cylinder into a first work chamber near the closed end and a second work chamber remote of the closed end, and a piston rod which is arranged on one side of the piston, penetrates the second work chamber and is guided out of the cylinder through a guiding and sealing device so as to be sealed. 
     A gas spring with a mechanical blocking device whose action depends upon internal pressure is known from German Patent DE 28 55 560 C2. The blocking device has a clamping body acting between a cylinder and piston rod. To form the blocking device, the piston comprises a pressure gas space formed by a ring piston and a piston cylinder which are displaceable relative to one another and are sealed by a seal, while the piston rod is guided through the piston so as to be sealed by seals and its ring piston and piston cylinder are displaceable on the piston rod, and the piston is supported by spring elements at stop bodies which are fixedly connected to the piston rod, a clamping body cooperating with the inner wall of the cylinder being arranged therebetween. 
     DE 36 17 726 C2 shows a gas spring with a deformable chamber whose interior space can be connected to the two work chambers of the gas spring by a flap valve. The flap valve is opened when the pressure in one of the work chambers is greater than a predefined pressure value in the deformable chamber. The flap valve is closed when there is a drop in pressure in the work chambers. Due to the difference in pressure which then exists between the work chambers of the gas spring and the deformable chamber, the wall of the deformable chamber is forced against either the piston rod or the inner wall of the work chambers so that the piston rod and piston are blocked. 
     It is the object of the invention to provide a gas spring of the type mentioned above which provides a mechanical fail safe becoming operative when there is a drop in gas pressure and which has a simple construction. 
     This object is met according to the invention in that the piston has a piston chamber which is connected to, or can be connected to, the outer environment of the cylinder, and a first safety element and a second safety element form the mechanical blocking device, wherein the first safety element connects the first work chamber to the outer environment via the piston chamber when the pressure in the cylinder is too low and brings the second safety element into contact with the inner wall of the cylinder. 
     In another construction, a second aperture located opposite from the first aperture is provided in the piston chamber and connects the piston chamber to the first work chamber. 
     A spring element is arranged in the piston chamber in order to pretension the first safety element axially in direction of the first work chamber by means of a slide. 
     The first safety element advantageously comprises a valve pin. 
     In another construction, a sealing element is arranged at the second aperture, the valve pin closing the second aperture by means of the sealing element such that it can open toward the first work chamber. 
     At least one sealing element is arranged at the first aperture so that the second aperture is closed tight against gas, and the valve pin closes the first aperture by means of this at least one sealing element such that the first aperture can open toward the bore hole of the piston rod. 
     In another construction, the second safety element comprises arms extending from the piston into the first work chamber. 
     Each arm has at its end remote of the piston a projection which narrows in diameter toward the piston so that an inclined surface is formed which is in operative connection with the first safety element. 
     Alternatively, the second safety element comprises a clamping element, preferably a plurality of clamping elements. 
     Every clamping element advantageously has a groove at the side facing the inner wall, an elastic ring element which pretensions the clamping elements radial to the center longitudinal axis being inserted into the groove. 
     In another construction, the clamping elements are fastened to the piston by means of wires so that the clamping elements are connected to the piston. 
     One or more circumferential inclined surfaces are formed one behind the other in axial direction at the side facing the center longitudinal axis. 
     In another construction, a clamping sleeve is arranged opposite the inclined surfaces so as to be concentric to the center longitudinal axis, this clamping sleeve having inclined surfaces which are formed so as to complement the other inclined surfaces. 
     The inclined surfaces are arranged at a defined distance from one another and form a ring-shaped intermediate space in which bearing elements in the form of balls or rollers are arranged. 
     In an advantageous construction, at least one supporting arm extends from the piston in direction of the first end of the cylinder, a holding element being arranged at its free end, which holding element is provided in turn as an axial stop for the clamping elements when the piston or piston rod moves in outward direction, wherein the supporting arm has, at the side facing the inner wall, a groove in which the ring element is arranged. 
     In an alternative construction, the first aperture connecting the piston chamber formed in the piston to the second work chamber has three portions with different inner diameters. 
     In another construction, the first portion remote of the piston chamber has an inner diameter which substantially corresponds to the outer diameter of the piston rod, one end of the hollow piston rod being inserted into the first portion, and material of the piston is folded into a radially circumferential groove arranged in the piston rod in order to connect the piston to the piston rod. 
     Following the first portion is a second portion with a smaller inner diameter in which a supporting ring and an O-ring seal are arranged, and the second portion is adjoined by a third portion with a further reduced inner diameter which directly communicates with the piston chamber, the three portions forming a step-shaped construction by means of the different inner diameters. 
     In an alternative embodiment form, the second aperture has a diameter which corresponds to the diameter of the piston chamber, and a circular space which is formed coaxial to the center longitudinal line in direction of the first work chamber and in which the slide is arranged adjoins the piston chamber. 
     In another construction, the space has a greater diameter than the piston chamber so that a step is formed at the transition from the space to the piston chamber, this step being contacted by the slide in normal operation. 
     Further, one or more supporting arms extend into the second work chamber from an annular wall surrounding the space, projections being provided at the free ends of the supporting arms. 
     In another embodiment form, the valve pin formed at the wedge element extends through the slide, the piston chamber and the three portions of the first aperture in direction of the piston rod, and the end of the valve pin facing the piston rod has an axial groove or flattened portion which is located in the first portion of the first aperture in normal operation. 
    
    
     
       Embodiment examples of the invention are shown in the drawings and are described more fully in the following. 
         FIG. 1  shows a longitudinal section through a gas spring according to the invention in normal operation; 
         FIG. 2  shows a longitudinal section through the gas spring shown in  FIG. 1  during a drop in pressure; 
         FIG. 3  shows a longitudinal section of another embodiment form of a gas spring according to the invention in normal operation; 
         FIG. 4  shows a detailed view of the gas spring shown in  FIG. 3  in normal operation; 
         FIG. 5  shows a detailed view of the gas spring shown in  FIG. 3  during a drop in pressure; 
         FIG. 6  shows a cross section through the gas spring shown in  FIG. 3 ; 
         FIG. 7  shows a longitudinal section through another embodiment form of a gas spring according to the invention in normal operation; 
         FIG. 8  shows a detailed view of the gas spring shown in  FIG. 7  in normal operation; 
         FIG. 9  shows a detailed view of the gas spring shown in  FIG. 7  during a drop in pressure; 
         FIG. 10  shows a cross section through the gas spring shown in  FIG. 7 ; 
         FIG. 11  shows a detailed view of another embodiment form according to the invention in longitudinal section; and 
         FIG. 12  shows a three-dimensional view of a structural component part shown in  FIG. 11 . 
     
    
    
       FIGS. 1 and 2  show a piston-cylinder unit in the form of a gas spring  1  comprising a cylinder  2  with a closed first end  3  and a second end  4  opposite from the closed end  3 . A piston rod  5  is guided out of the cylinder  2  in a sealed manner concentric to a center longitudinal axis A of the gas spring  1  through the second end  4  by means of a guiding and sealing device  6 . 
     Normally, a connection element, not shown, in the form of a ball socket or knuckle eye is arranged at the closed end  3  of the cylinder  2 , and another connection element, not shown, by which the gas spring  1  is fastened between two parts which are movable relative to one another, for example, a hatch and a body of a motor vehicle, is arranged at the end of the piston rod  5  located outside the cylinder  2 . 
     A piston  7  is arranged at the end of the piston rod  5  located in the cylinder  2  and divides the cylinder  2  into a first work chamber  8  and a second work chamber  9  through which the piston rod  5  extends. Overflow devices, not shown, which are assumed as known in gas springs, for example, a groove extending in axial direction in the cylinder  2  or a piston ring under which flow can occur, can be provided so that the gas which is under pressure in the cylinder  2  can flow from one work chamber into the other. The piston ring shown in the drawings is a simple O-ring  7   a.    
     A piston chamber  10  is formed in the piston  7  and has, at the side of the piston  7  facing the second work chamber  9 , a first aperture  10  which is arranged concentric to the center longitudinal axis A and which opens into a bore hole  12  extending through the piston rod  5 . A second aperture  13  formed concentric to the center longitudinal axis is provided on the side opposite from the first aperture  11  and joins the piston chamber  10  with the first work chamber  8 . On the side facing the first work chamber  8 , the second aperture  13  has a widened diameter  14  in which a sealing element  15  is arranged. 
     Arranged in the piston chamber  10  is a spring element  16  which contacts the inner wall of the piston chamber  10  facing the second work chamber  9  and contacts a disk-shaped slide  17  on the opposite side. The slide  17  in turn contacts a valve pin  18  or is connected integral with it. The valve pin  18  extends from the piston chamber  10  through the second aperture  13  into the first work chamber  8  and comprises a first portion  19  having a small diameter, the diameter of the first portion  19  being at least slightly smaller than the inner diameter of the second aperture  13 , and a second conically shaped portion  20 . 
     At the side opposite the first portion  19 , the second portion  20  of the valve pin  18  is connected to a truncated-cone-shaped wedge element  22  which, together with the valve pin  18 , forms a first safety element  23 . The valve pin  18  and the wedge element  22  can be screwed, glued, or welded together, for example. It is also possible for the valve pin  18  and wedge element  22  to be formed integral with one another. 
     A plurality of arms  25  forming a second safety element  24  extend from the piston  7  into the second work chamber  9 . The arms  25  have a projection  26  at their ends remote of the piston  7 . The projection  26  narrows in diameter toward the piston  7  so as to form an inclined surface  27  in operative connection with the first safety element  23 . 
     In normal operation, as is shown in  FIG. 1 , the second portion  20  of the valve pin  18  is tightly pressed against the sealing element  15  by the gas pressure in the gas spring. 
     When there is a decrease in gas pressure, for example, due to lost gas, the force of the spring element  16  arranged in the piston chamber  10  is greater than the effective gas force acting on the valve pin  18 . As is shown in  FIG. 2 , the valve pin  18  is moved axially in direction of the first end  3  of the cylinder  2  and the conical second portion  20  is lifted from the sealing element  15 . In this way, an immediate area compensation is brought about at the valve pin  18  so that the acting gas force is not dependent on direction and the force of the spring element  16  moves the valve pin  18  quickly in direction of the first end  3  of the cylinder  2  without an opposing force being exerted by the gas pressure. 
     The first safety element  23  formed by the valve pin  18  and wedge element  22  is displaced by the force of the spring element  16  against the inclined surfaces  27  of the arms  25  and moves the latter radially against the inner wall  28  of the cylinder  2  so that there is a drastic increase in friction and, accordingly, a blocking of the piston  7  and, therefore, of the piston rod  5  is carried out. 
     In the embodiment form shown in  FIGS. 3 to 6 , the second safety element  24 ′ comprises a plurality of clamping elements  29  arranged circumferentially near the inner wall  28 . Each of the clamping elements  29  has a groove  30  on the side facing the inner wall  28 , an elastic ring element  31 , for example, an O-ring made of an elastomer or an annular spring, being inserted into the groove  30 . The ring element  31  pretensions the clamping elements  29  radially inward and is inserted into the groove  30  to a depth such that the ring element  31  does not touch the inner wall  28  of the cylinder  2  even when the clamping elements  29  are moved in radial direction against the inner wall  28 . The clamping elements  29  are fastened to the piston  7  by wires  32 . Preferably two circumferential inclined surfaces  33  are formed one behind the other at the side facing the center longitudinal axis A. 
     Opposite the inclined surfaces  33 , a clamping sleeve  34  having inclined surfaces  35  complementing the inclined surfaces  33  is arranged concentric to the center longitudinal axis A. The clamping sleeve  34 , together with the wedge element  22  and valve pin  18 , forms the first safety element  23 ′. The inclined surfaces  33  and  35  are arranged at a defined distance from one another and form a ring-shaped intermediate space  36  in which bearing elements  37  in the form of balls or rollers are arranged. The inclined surfaces  33  and  35  are constructed in such a way that the bearing elements  37  cannot fall out of the intermediate space  36 . For this purpose, a collar  38 , for example, which can be contacted by the bearing elements is formed at the ends of the inclined surfaces  33  and  35 . Further, the clamping sleeve  34  has an inner cone  39  fitted to the wedge element  22 . 
     In the event of a drop in pressure due to the escape of gas from the cylinder  2 , the spring element  16  moves the valve pin  18  and, therefore, the wedge element  22  and clamping sleeve  34  along the center longitudinal axis A in direction of the first end  3  of the cylinder  2  as is shown in  FIG. 5 . At the same time, the piston  7  with the piston rod  5  moves into the cylinder  2 . A self-reinforcing clamping at the inner wall  28  is produced in this way by the clamping elements  29  which are fixedly connected to the piston  7  in the pull direction by the wires  32 . In doing so, the bearing elements  37  reduce the friction between the clamping sleeve  34  and the clamping elements  29 . The self-reinforcement of the clamping elements  29  occurs when the friction angle between the outer clamping elements  29  and the inner wall  28  of the cylinder  2  is greater than the sum of the friction angle between the clamping sleeve  34  and clamping elements  29  and the selected angle of inclination or wedge angle α. 
       FIGS. 7 to 10  show another embodiment form of the invention in which the wedge element  22  and the clamping sleeve  34  shown in  FIGS. 3 to 6  are formed integral with one another. Three supporting arms  40  extend from the piston  7  in direction of the first end  3  of the cylinder  2 , a holding element  42  being arranged at their free ends  41 . The holding element  42  is provided in turn as an axial stop for the clamping elements  29  when the piston  7  and piston rod  5  move in the outward direction. The supporting arms  40  have a groove  43  on the side facing the inner wall  28 . In this embodiment example, the ring element  31  is arranged in the grooves  30  of the clamping elements  29  and in the grooves  43  of the supporting arms  40 . 
     As is shown in  FIG. 10 , the bearing elements  37  are constructed as rollers and the first safety element  23 ′ has, in the area where it cooperates with the second safety element  24 ′, a cross section substantially corresponding to the shape of a triangle with rounded corners. In case gas escapes from the cylinder  2 , the spring element  16  moves the first safety element  23 ′ along the center longitudinal axis A in direction of the first end  3  of the cylinder  2  as is shown in  FIG. 9 . At the same time, still more gas is released into the environment from the cylinder  2 , and the piston  7  moves with the piston rod  5  into the cylinder  2  owing to the lost gas, and the clamping elements  29  move radially outward against the inner wall  28  of the cylinder  2  by means of the bearing elements  37 . In so doing, a self-reinforcing clamping is brought about at the inner wall  28  by the clamping elements  29  which are connected to the piston  7  in the pull direction by the holding element  42 . 
       FIG. 11  shows a detailed view of another embodiment form of the invention. The first aperture  11  which connects the piston chamber  10  formed in the piston  7  to the bore hole  12  in the piston rod  5  has three portions with different inner diameters. The first portion  44  which is remote of the piston chamber  10  has an inner diameter which substantially corresponds to the outer diameter of the piston rod  5 . One end of the hollow piston rod  5  is inserted into the first portion  44 . Material of the piston  7  is deformed into a radially circumferential groove  45  arranged in the piston rod to connect the piston  7  to the piston rod  5 . Adjoining the first portion  44  is a second portion  46  with a smaller inner diameter in which a supporting ring  47  and an O-ring seal  48  are arranged. Adjoining the second portion  46  is a third portion  49  with a further reduced inner diameter which communicates directly with the piston chamber  10 . The different inner diameters of the three portions  44 ,  46  and  49  form a step-shaped construction by which the supporting ring  47  and the O-ring seal  48  are fixed in axial direction. 
     The second aperture  13  opposite the first aperture  11  has a diameter corresponding to the diameter of the piston chamber  10 . Adjoining the piston chamber  10  is a circular space  50  which is formed coaxial to the center longitudinal line A and in which the slide  17  is arranged. The space  50  has a greater diameter than the piston chamber  10  so that a step  51  is formed at the transition from the space  50  to the piston chamber  10 , this step  51  being contacted by the slide  17  in normal operation. However, it can be seen that the slide  17  can be formed integral with the wedge element  22 . The supporting arms  40  extend from an annular wall  52  surrounding the space  50  into the first work chamber  8 . In another construction, projections  53  are provided at the free ends of the supporting arms  40 , which projections  53  serve as stops for the clamping elements  29  when the piston rod  5  is moved out of the cylinder  2 . 
     The valve pin  18 ′ formed at the wedge element  22  extends through the slide  17 , piston chamber  10 , and the three portions  44 ,  46  and  49  of the first aperture  11  in direction of the piston rod  5 . The end of the valve pin  18 ′ facing the piston rod  5  has an axial groove or flattened portion  54  which is located in the first portion  44  of the first aperture  11  in normal operation. 
     When there is a loss of pressure, the spring element  16  moves the slide  17  and, therefore, the first safety element  23 ′ along the center longitudinal axis A in direction of the first work chamber  8 . The groove or flattened portion  54  of the valve pin  18 ′ enters the second portion  46  of the aperture  11  and still more gas escapes. At the same time, the piston  7  moves with the piston rod  5  into the cylinder  2  owing to the lost gas, and the clamping elements  29  move radially outward against the inner wall  28  of the cylinder  2  by means of the bearing elements  37 . In this way, a self-reinforcing clamping is brought about at the inner wall  28  by the clamping elements  29  which are connected to the piston  7  in the pull direction by the projections  53 . 
       FIG. 12  shows the piston shown in  FIG. 11  in a three-dimensional view which clearly shows the arrangement of the projections  53  at the supporting arms  40 . 
     REFERENCE NUMBERS 
     
         
           1  gas spring 
           2  cylinder 
           3  first end 
           4  second end 
           5  piston rod 
           6  sealing and guiding device 
           7  piston 
           7   a  piston ring 
           8  first work chamber 
           9  second work chamber 
           10  piston chamber 
           11  first aperture 
           12  bore hole 
           13  second aperture 
           14  expanded diameter 
           15  sealing element 
           16  spring element 
           17  slide 
           18  valve pin 
           18 ′ valve pin 
           19  first portion 
           20  second portion 
           22  wedge element 
           23  first safety element 
           23 ′ first safety element 
           24  second safety element 
           24 ′ second safety element 
           25  arm 
           26  projection 
           27  inclined surface 
           28  inner wall 
           29  clamping element 
           30  groove 
           31  ring element 
           32  wire 
           33  inclined surface 
           34  clamping sleeve 
           35  inclined surface 
           36  intermediate space 
           37  bearing element 
           38  collar 
           39  inner cone 
           40  supporting arm 
           41  free end 
           42  holding element 
           43  groove 
           44  first portion 
           45  groove 
           46  second portion 
           47  supporting ring 
           48  O-ring seal 
           49  third portion 
           50  space 
           51  step 
           52  annular wall 
           53  projection 
           54  flattened portion 
         A center longitudinal axis