Abstract:
A damper has a cylinder and a piston, the piston having two or more parts. A first piston part is made of a rubber-elastic material forced against the cylinder wall during a damping stroke. A second piston part is made of a material that is stiffer in comparison to the rubber-elastic material. The second piston part as seen in the radial direction lies between an area of the first piston part and the cylinder wall. The first piston part may have at least two sections of different hardnesses over its lengths. The piston could also include a piston part that is radially forced outwards to rub against the cylinder wall during damping, the piston part being made as a solid body of a material with rubber-elastic properties which becomes flattened under pressure, deforming in such a way that a friction seal is created between the piston part and the cylinder wall.

Description:
REFERENCE TO RELATED APPLICATION 
     This is a continuation of PCT/AT2003/000367, filed Dec. 11, 2003 and designating the United States. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a damper, especially for movable furniture parts, with a cylinder and a piston movable therein. The piston comprises two or more parts, including a first piston part consisting of rubber-elastic material which is forced against the cylinder wall during the damping stroke, and including a second piston part consisting of a material which is stiffer in comparison to the rubber-elastic material, especially a rigid material. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve the braking behavior of the piston of such a damper and to reduce its wear. 
     The object of the invention is met in that the second piston part—seen in a radial direction—lies between an area of the first piston part and the cylinder wall. 
     One embodiment of the invention provides that the first piston part is taken up in a frontal recess of the second piston part. 
     In a further embodiment of the invention, provision is made that the first piston part has a snap ring groove in the area adjacent to the second piston part. 
     A further embodiment of the invention makes provision that the second piston part encircles the mantle of the first piston part in the manner of a belt, whereby for preference the second piston part is designed as a network which encircles the first piston part. 
     A further preferred embodiment of the invention makes provision that the first piston part has at least two, preferably more, sections of different hardness over its length. 
     A further preferred embodiment of the invention provides that the piston is produced in the form of a solid body made from a material with rubber-elastic properties and becomes flattened under pressure whereby it deforms in such a way that a friction seal is created between the piston part and the cylinder wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the invention will be described with the aid of the figures in the attached drawings, which show: 
         FIG. 1  is a side view of an inventive damper, 
         FIG. 2  is a section view along line A—A of  FIG. 1 , 
         FIG. 3  is section view A from  FIG. 2 , 
         FIG. 4  is a side view of an inventive damper after damping has been effected, 
         FIG. 5  is a section view along line B—B of  FIG. 4 , 
         FIG. 6  is a section view A from  FIG. 5 , 
         FIG. 7  is a section view along line A—A of  FIG. 1 , wherein a further embodiment of a piston is shown, 
         FIG. 8  is a section view A from  FIG. 7 , 
         FIG. 9  is a section view along line A—A of  FIG. 1 , wherein a further embodiment of a piston is shown, 
         FIG. 10  is a section view A from  FIG. 9 , 
         FIG. 11  is a section view along line A—A of  FIG. 1 , wherein a further embodiment of a piston is shown, 
         FIG. 12  is a section view A from  FIG. 11 , 
         FIG. 13  is a section view along line A—A of  FIG. 1 , wherein a further embodiment of a piston is shown, 
         FIG. 14  is a section view A from  FIG. 13 , 
         FIG. 15  is a section view along line A—A of  FIG. 1 , wherein a further embodiment of a piston is shown, 
         FIG. 16  is a section view A from  FIG. 15 , 
         FIG. 17  is a longitudinal section view through a cylinder and a piston, showing the piston in the ready position, 
         FIG. 18  is a longitudinal section view through a cylinder and a piston, showing the piston in the damping position, 
         FIG. 19  is a schematically shown section view through a further embodiment of an inventive damper, showing the piston in the ready position, 
         FIG. 20  is a schematically shown section view through the inventive damper, showing the piston during damping, 
         FIG. 21  is a schematically shown section view through the inventive damper, showing the piston at the end of the damping path once damping has been completed, 
         FIGS. 22–24  are views similar to  FIGS. 19 to 21  of a second embodiment of the piston, 
         FIG. 25  is a view of a piston in the ready position, and 
         FIG. 26  is a view of the piston during the damping process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, the embodiments will be described in accordance with  FIGS. 1 to 18 : 
     The inventive damper, in a conventional manner, includes a cylinder  1  in which a piston  2  is linearly displaceable. The piston  2  in the embodiments according to  FIGS. 1 to 16  includes a first piston part  3  made from a rubber-elastic material and a second piston part  4  made from a harder material than the first piston part  3 . The second piston part  4  can be made from a plastic, or from a die-cast alloy or similar material. In the embodiments shown, the second piston part  4  is designed integral with a piston rod  5 . The piston rod  5  has ribs  6 , which improve the guidance of the piston rod  5  in the cylinder  1  and thereby keep the friction between the piston rod  5  and the cylinder  1  low. The first piston part  3  has a main body and a lip  7  on its distal end furthest away from the second piston part  4 . The front wall  1 ′ of the cylinder  1  is provided with an opening  8  which allows for the escape of a damping fluid, in this case air, during damping. As shown in, for example,  FIG. 3 , the piston  2  and the cylinder  1  are shaped and arranged so that, when no pressure is applied in the “F” direction, there is a gap formed between the piston  2  and the wall of the cylinder  1  at least partially around the piston  2 . 
     The first piston part  3  has a peg-type projection  9  by which it is anchored in the second piston part  4 . The projection  9  is provided with a spread ring  10 , which is taken up in a chamber-shaped recess  11  in the second piston part  4 . The projection  9  is axially displaceable in the recess  11  with its spread part  10 . The first piston part  3  and the sealing lip  7  are preferably made from a rubber-elastic material, for example from liquid silicon rubber (LSR), thermoplastic elastomer (TPE) or silicon rubber. The range of hardness of the first piston part  3  preferably lies between 40 A and 85 A Shore. 
     The second piston part  4  has a three-dimensionally curved (i.e., concave) frontal recess  13 , which is designed at least approximately in the form of a spherical cap. The first piston part  3  is arranged with its base end in this recess  13 . The base end  14  of the first piston part  3  can be designed either cylindrically or as a truncated cone. 
     In the ready position, i.e. when no force is acting upon the piston rod  5  and thus the second piston part  4  is not being forced against the first piston part  3 , the base end  14  of the first piston part  3  does not completely fill the recess  13 . As can be seen, for example, from  FIG. 3 , the end  14  of the piston part  3  protrudes over approximately half the radius of the recess  13  into the recess  13 . 
     If a force is exerted on the end  12  of the piston rod  5 , the piston rod  5  and the piston  2  are moved in the direction of the arrow F. Due to the resistance of the damping medium, for example air, the first piston part  3  is compressed by deformation during the damping process as shown in  FIGS. 5 and 6  and thereby radially expanded. As a result of this expansion a friction seal is created between the main body of the first piston part  3  and the cylinder wall  15 . The resistance of the damping medium is further increased by the sealing lip  7  of the first piston part  3 , and the lip  7  abuts against the cylinder wall  15  from the start of the motion of the piston (i.e., which always abuts against the cylinder wall to provide a constant sealing effect). 
     During this damping motion, the base end  14  of the first piston part  3  is pressed into the recess  13 , until, as shown in  FIGS. 5 and 6 , it is taken up more or less completely in the recess (i.e., substantially fills the recess  13 ). Due to the fact that the base end  14  of the first piston part  3  is taken up in the recess during damping, the first piston part  3  is deformed and the friction forces between the first piston part  3  and the cylinder wall  15  are distributed over the entire length of the first piston part  3 . Thus, peak forces are prevented in the area where the first piston part  3  rests on the second piston part  4 . The first piston part  3  is advantageously tapered conically from the sealing lip  7  towards the base end  14 , which additionally contributes to a distribution of the friction forces. 
     In the embodiment according to  FIGS. 7 and 8 , the first piston part  3  is provided with a snap ring groove  16  near its base end  14 . The snap ring groove  16  contributes to the further unloading of the friction forces in the rear area of the first piston part  3 . It is essential that during the entire damping process, a part of the second piston part  4 , which is the harder piston part, lies between the base end  14  of the softer first piston part  3  and the cylinder wall  15  with respect to the radial direction. The softer piston part  3  thus cannot be forced against the cylinder wall  15  over its entire length. 
     In the embodiment according to  FIGS. 9 and 10 , the first piston part  3  comprises two sections  3 ′,  3 ″ of different hardnesses. The distal section  3 ″ lying nearer to the lip  7  gives way more quickly because it is made from a softer material. The intended result of this is that the entire surface of the piston part  3  abuts against the cylinder wall  15  right from the start of the braking process. This effects a more even distribution of force over the piston part  3 . This results in smaller peak forces during the braking process and less wear. 
     In the embodiment according to  FIGS. 11 and 12 , the first piston part  3  is provided with a cavity  18 , which is located in its rear area, i.e. facing towards the second piston part  4 . In other words, the cavity  18  is located at the base end of the first piston part  3 . The cavity  18  allows a targeted influence on the surface pressure, thus the distribution of friction force over the piston part  3 . The surface pressure is reduced at the site of the cavity  18 . Should, for example, the intention be for wear to be minimized by a harder elastomer as the material of the first piston part  3 , the annular gap between the piston part  3  and the cylinder wall  15  must be selected to be very small, since harder materials become effective later during the damping process. If no cavity  18  is provided, the small annular gap between the piston part  3  and the cylinder wall  15  can lead to an abrupt braking at the end of the braking/damping path. The result would be an unpleasant braking process. 
     Instead of a cavity  18 , a filling area within the first piston part  3  which is formed of a softer material could also be provided. 
     In the embodiment according to  FIGS. 13 and 14 , the first piston part  3  is provided with a mantle area (i.e., main body portion)  19  tapering conically towards the sealing lip  7 . On its base end located towards the second piston part  4 , the first piston part  3  has a cylindrical graduation  20 . By greater or lesser conicity of the area  19 , the surface pressure can be decreased or increased in a controlled fashion over the length of the piston part  3 . The graduated section  20  prevents any excessive surface pressure in the area of attachment to the second piston part  4 . 
     In the embodiment according to  FIGS. 15 and 16 , the first piston part  3  has several snap ring grooves  21  and several piston lands  22 , which alternate over the entire length of the piston part  3 . The diameters of the piston lands  22  here decrease in a direction from the sealing lip  7  to the second piston part  4 . In the embodiment according to  FIGS. 17 and 18 , the first piston part  3  is encircled by a network  23 . The network  23  is made from a harder material than the piston part  3  and forms the second piston part. The first piston part  3  rests directly on a bolster plate  24  which is connected with a piston rod  25 . During the damping process, as can be seen from  FIG. 18 , bulges  26  of the piston part  3  are pressed against the cylinder wall  15 . 
     In all embodiments, a more even surface pressure of the piston part  3  on the cylinder wall  15  is achieved. This causes less wear and a better braking behavior, i.e. the braking behavior is less abrupt. 
     In the embodiment according to  FIGS. 19 to 24 , a cylindrical first piston part  3  abuts against a second piston part  4  which is designed as a bolster plate. In the cylinder  1  there is a compression spring  27 , which rests, firstly, on one front wall  1 ′ of the cylinder  1  and secondly on the front side of the piston  2 . The second piston part  4  is connected to a piston rod  5 . The first piston part  3  is provided at the front with a sealing lip  7 , which abuts against the cylinder wall  15 . The term “at the front” means in the direction of motion of the piston  2  during the damping process. 
     The front wall  1 ′ of the cylinder  1  has, in turn, an opening  8 , which allows the escape of the damping fluid, in this case, air. 
     During the damping process, a force acts on the base end  12  of the piston rod  5 , and the piston  2  is moved in the direction of the arrow F. 
     Due to the resistance of the damping medium, for example air, the first piston part  3  is flattened during the damping process as shown in  FIG. 20  and thereby radially expanded. As a result of this expansion, a friction seal is created between the piston part  3  and the cylinder wall  15 . 
     At the end of the damping path, the first piston part  3  expands in the axial direction due to its own elasticity, whereby the compression spring  27  is further compressed. 
     Since the friction seal between the first piston part  3  and the cylinder wall  15  is cancelled out due to this axial expansion of the piston part  3 , the compression spring  27  of the piston  2  can move back into the ready position. 
     In the embodiment according to  FIGS. 19 to 21 , the main body portion of the first piston part  3  and the sealing lip portion  7  form a monolithic (one-piece) body. The first piston part  3  and the sealing lip  7  are in this instance made from a rubber-elastic material, for example from liquid silicon rubber (LSR), thermoplastic elastomer (TPE) or silicon rubber. The range of hardness of the piston preferably lies between 40 A and 85 A Shore. 
     In the embodiment according to  FIGS. 22 to 24 , the piston part  3  and the sealing lip  7  consist of different materials. However, the sealing lip  7  is joined to the first piston part  3 , for example glued or welded, so that the first piston part  3  and the sealing lip  7  can be regarded in functional terms as one piece. The advantage of this execution can be seen in that the piston part  3  and the sealing lip  7  can have different elastic properties. 
     As can be seen from  FIGS. 25 and 26 , the piston part  3  can be provided with an axial groove  28  on the mantle, which enables the through-flow of the damping fluid within the cylinder  1  from one side of the piston  2  to the other side of the piston  2  during the damping process. 
     The inventive damper can be used, for example, in drawers, furniture doors or hatches. It can advantageously be combined with a retracting or closing device as described in the German utility model DE 202 18 067.