Patent Publication Number: US-7581485-B2

Title: Working cylinder with terminal position damping

Description:
FIELD OF THE INVENTION 
   The invention relates to a working cylinder with end position damping, which has a cylinder body that contains a cylinder chamber, the cylinder body for instance being in the form of a tube or an extruded profile section; two end parts that close the cylinder on its ends; a piston supported longitudinally displaceably in the cylinder chamber between two end positions; and a device for damping the motion of the piston upon the approach to a at least one of its end positions. 
   BACKGROUND OF THE INVENTION 
   Pressure medium-actuated working cylinders often have end position damping to assure impact-free working action of the working cylinder. One example of such a pressure medium-actuated working cylinder with end position damping is described in U.S. Pat. No. 6,758,127. In this working cylinder, an axially protruding, tubular, cylindrical damping pin is provided on each of the two face ends of the piston, and associated with the damping pin is a receiving opening in the respective end piece, toward it, of the cylinder body, into which opening the damping pin plunges upon the approach of the piston to its end position. The receiving opening is in communication with a device for throttled the diversion pressure medium enclosed in the damping chamber. The length of the path that the piston travels upon approach to an end position, from the position in which the damping pin is just beginning to penetrate into the receiving opening and closes the damping chamber, until the position in which the piston has reached its actual terminal position and for instance rests with its face end on the face end of the associated end part, is called the damping stroke. The length of this damping stroke is predetermined by the axial length of the damping pin and hence by the depth of the receiving opening, which in turn is limited by the axial dimensions or in other words the thickness of the end part. Since the installed length of a working cylinder is often predetermined, for instance by standards, for a given piston stroke, the damping stroke cannot be made arbitrarily long. 
   On the other hand, particularly when relatively large masses are in motion, a longer damping distance, or in other words a longer damping stroke, is appropriate, since by that means the kinetic energy of the moving masses can be better dissipated, which leads to lesser reaction forces on the subconstruction and usually also improves adjustability, especially with additional elements. In an end position—damped working cylinder known from German Utility Model DE 297 06 364 U1, the main piston of the working cylinder is preceded by a control piston, which carries a ring magnet and which is connected to the main piston via cone springs and slides displaceably on the piston rod. The control piston simultaneously serves a blocking device and as a valve for outflow conduits, and upon contact of the control piston with the respective end part of the working cylinder, a damping impoundment chamber is embodies, from which fluid can flow away via a throttled outflow bore. Although this working cylinder does have a longer damping path or stroke in comparison to the aforementioned prior art, nevertheless the cone spring requires additional installation space, which is in addition to the fact that the use of spring elements, because of their limited service life, is problematic in many applications. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is therefore the object of the invention to create a working cylinder with end position damping whose damping device is distinguished by a simple, operationally reliable construction and which, with a limited installed length of the entire working cylinder, has a long damping stroke. 
   For attaining this object, in the novel working cylinder, the device for damping the motion of the piston upon the approach to at least one of its end positions has two cooperating damping elements, of which one is provided on an end part of the working cylinder and the other is provided on the piston, on its side toward that end part. The two end parts, upon the approach of the piston to its end position, close a damping chamber, which communicates with a device for throttled diversion of pressure medium enclosed in the damping chamber. To that end, the two damping elements are insertable axially into one another in telescoping fashion in the direction of the piston motion, for instance in that one of the two damping elements has a receiving opening embodied in the end part or the piston, and the other has a telescoping damping pin that is insertable in sealed fashion into the receiving opening. In a preferred embodiment, the damping pin has a sleeve, which is supported in limited axial displacement on a rodlike bearing part that protrudes axially toward the piston or the end part. In a working cylinder that has a piston rod extended through an end part, the bearing part can directly be part of the piston rod. 
   Of the two damping elements that are insertable into one another upon the approach of the piston to its end position, as least one is supported for limited longitudinal displacement on the end part or the piston between two axially spaced-apart terminal positions with respect to the piston or the end part as applicable. Both damping elements are provided with cooperating inhibiting means, under whose influence the longitudinally displaceable damping element, upon a movement of the piston away from its end position, is adjustable into a terminal position, which is farther away from the piston than a first terminal position that the damping element normally assumes. The displaceability of the one damping element relative the piston or the end part produces an additional damping stroke by a telescoping action of the parts sliding in one another upon the approach of the piston to its end position. The inhibiting means assure that upon the motion of the piton away from its end position, the longitudinally displaceable damping element returns to its outset position without requiring additional actuation devices, such as spring elements or the like, for doing so. Hence no additional installation space is needed. The simple construction moreover allows the use of parts produced on a near-mass-production basis even for long damping strokes, that is, long damping paths. 
   The working cylinder may be either a single- or double-acting working cylinder, with a piston rod extended through at least one of its end parts, but the concept of the invention can also be applied equally to cylinders without piston rods. The working cylinders are as a rule pressure medium-actuated, for instance being pneumatic cylinders, but a corresponding device for end position damping can also be provided in working cylinders or linear drives that have a different form of actuation, for instance via Bowden cables and the like. 
   Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal section of a working cylinder in accordance with the invention, showing a middle stroke position of a piston of the working cylinder; 
       FIG. 2  is an enlarged view of a detail “Y” of the working cylinder of  FIG. 1 ; 
       FIG. 3  is an enlarged view of a detail “Z” of the working cylinder of  FIG. 1 ; 
       FIG. 4  shows the working cylinder of  FIG. 1  in a corresponding sectional view, showing a stroke position of the piston in which the two damping elements of the end position damping device are just entering into engagement with one another; 
       FIG. 5  shows the working cylinder of  FIG. 1  in a corresponding sectional view, showing a stroke position of the piston in which the two damping elements of the end position damping device are inserted all the way into one another; 
       FIG. 6  shows the working cylinder of  FIG. 1  in a corresponding sectional view, showing a stroke position of the piston in which the piston has reached its end position; 
       FIG. 7  shows the working cylinder of  FIG. 1  in a corresponding sectional view, showing a stroke position of the piston in which the piston has moved partly away from its end position again; and 
       FIG. 8  is a longitudinal section of a piston-rodless working cylinder in accordance with the invention, showing a stroke position of the piston in which the piston is approaching its end position, and the two damping elements have already entered into engagement with one another. 
   

   While the invention is susceptible of various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now more particularly to  FIGS. 1-7  of the drawings, there is shown an illustrative working cylinder in accordance with the invention, which is in the form of a pneumatic cylinder having a cylinder body in the form of a cylindrical tube  1  and two end parts  2 ,  3  connected to the cylindrical tube  1  in a sealed fashion. The cylindrical tube  1  surrounds a cylinder chamber in which a piston  4 , which is sealed off from the inner wall of the cylindrical tube  1  via piston ring seals, is longitudinally displaceably. The piston  4  divides the cylinder chamber into two cylinder or pressure compartments  6 ,  7 , which are separated by the piston  4 . 
   A coaxial cylindrical piston rod  8  is fixed to the piston  4  and is guided through the end part  2  in sealed fashion. A piston rod seal is shown at  9 . The piston rod  8  that crosses through the cylinder compartment  6  is lengthened on the diametrically opposite side of the piston. On its lengthened portion  10 , a coaxial cylindrical bush  11  protrudes into the cylinder compartment  7  and is fixed to the piston  4  by a screw  12  that is screwed to the lengthened portion  10  of the piston rod. 
   One connection conduit  14 , opening into a threaded bore  13 , is provided in each of the two end parts  2 ,  3  and can be made to communicate, via a corresponding screwed-in connection fitting, with a compressed air source, or a ventilator, in each case via suitable valves, and which on its other sides opens into a respective cylindrical, cup-shaped receiving opening  15 , which discharges into the cylinder compartment  6  and  7 , respectively, on the side of the respective end part  2  and  3  oriented toward the piston  4 . The receiving opening  15  is coaxial with the piston rod is closed on the side away from the piston  4  in both end parts  2 ,  3 , which in the case of the end part  2  is achieved by the piston rod seal  9 , while the receiving opening  15  in the other end part  3  is closed off by an integrally formed-on bottom part  16 . Each of the two receiving openings  15  contains an elastic sealing element, in the form of an O-ring  20 , that extends all the way around in an annular groove  18  in the vicinity of the mouth of the receiving opening. The axial depth of the two receiving openings  15  is as a rule the same and is dimensioned such that a maximum depth  21  is achieved without increasing the installed length of the working cylinder. 
   The receiving opening  15  in each of the two end parts  2 ,  3  forms a respective damping element of a device for end position damping of the piston  4 . For that purpose, it cooperates with a second damping element, which is provided on the piston  4  and has a respective telescoping damping pin, which upon the approach of the piston to its respective end position is insertable in sealed fashion into the respective receiving opening  15 , in order to define a damping chamber, which encloses pressure medium which effects a pneumatic damping of the piston motion upon the throttled outflow from the receiving opening. 
   The second damping element, cooperating with the receiving opening  15 , has a cylindrical sleeve  19 , which is supported for limited axial longitudinal displacement on the piston rod  8  on the side of the piston  4  toward the end part  2  on the cylindrical bush  11  on the side of the piston toward the other end part  3 . On its side toward the respective end part  2 ,  3 , the sleeve  11  is chamfered on the outside at  22 , while on its diametrically opposed end it is formed with an annular flange  23 , which defines a stop face  24  oriented toward the respective end part  2 ,  3 . In the face end of the piston toward it, the annular flange  23  of each of the two sleeves  19  has a respective annular groove  25 , which is capable of receiving the entire annular flange  23 , as will be described in detail hereinafter. 
   As can be seen particularly from the detail “Z” in  FIG. 3 , each sleeve  19 , in the region of its inner wall, has an annular shoulder  26 , which cooperates with a corresponding annular shoulder  27  near the free end of the tube  11  on one side of the piston and with an annular shoulder  28  on the piston rod  8  on the other side of the piston. The annular shoulders  27 ,  28  are spaced apart from the respective adjacent face end of the piston so far, and are adapted in such a way to the length of the sleeve  19 , that in the first terminal position, far from the piston, shown in  FIG. 1 , in which the annular shoulders  26 ,  27  and  26 ,  28  rest on one another, the two sleeves  19  with their annular flange  23  are at the same axial spacing from the adjacent face end of the piston, and that in a second terminal position, near the piston, the flange  24  is in each case received entirely in the respective annular groove  25 , as is shown in  FIG. 6  for the sleeve  19  associated with the end part  3 . 
   In the first terminal position shown in  FIG. 1 , the two sleeves  19  are unlocked. The associated detent device has a detent element, in the form of an O-ring  31 , which is in an annular groove  29  and  30  of the piston rod  8  and the bush  11 , respectively, and which elastically resiliently cooperates with a detent indentation  32  on the inner wall of the sleeve  19 . In the first terminal position shown, the sleeve  19  adjacent to the end part  3  protrudes axially past the bush  11  over a great proportion of the length of the sleeve, while the other sleeve  19 , over the greatest proportion of its length, rests on a portion of larger diameter of the piston rod  8 . Instead of the detent locking, a frictional engagement locking of the sleeves may be employed. 
   An annual bead  320  extending all the way around furthermore is provided on the two sleeves  19 , for instance adjoining the chamfer  22 ; it can cooperate with the respective O-ring  20  in the end part  2  and  3 , respectively, and together with this O-ring it forms inhibiting means for the axial motion of the sleeve  19  oriented away from the respective end part, as will be described below. 
   The two receiving openings  15  in the end parts  2 ,  3  each are provided with a device for throttled diversion of pressure medium enclosed in the damping chamber that is surrounded by the piston  4 , the cylinder chamber  6  or  7  and the end part  2  and  3 , respectively. In the illustrated embodiment, this device includes a throttle valve  33 , which is shown in its details in the detail “Y” in  FIG. 2 . The throttle valve  33  is inserted into a corresponding bore  34  in the respective end part  2  and  3 , which communicates with the receiving opening  15  via a coaxial conduit  35  and with the cylinder compartment  6  and/or  7  via a laterally outgoing conduit  36 . 
   The throttle valve  33  has a valve body  37 , which is pressed elastically by a valve spring  38  against a valve seat  39 ; the valve spring  38  being braced axially against a stopper  400  screwed into the bore  34 . The valve body  37  in this case is in the form of a differential piston. If the same pressure of the pressure medium prevails in both conduits  35 ,  36 , then the valve spring  38  can keep the valve body  37  on the valve seat  39  and can thus keep the throttle valve closed ( FIG. 2 ). If the pressure rises in the damping chamber, and thus in the conduit  35 , by a preset value, then the valve body  37  is correspondingly lifted from the seat  39 . A throttle conduit  40  of relatively small diameter is formed in the valve body  37 , and by way of it, when the valve is closed, air can flow out of the damping chamber into the adjacent, pressureless cylinder chamber  6  or  7  as applicable. The throttle conduit  40  acts as a bypass conduit. 
   The end position damping of the working cylinder described functions as follows: 
   In the middle stroke position of the piston  4 , shown in  FIG. 1 , the two sleeves  19 , each acting as a longitudinally displaceable damping element, are shown in their terminal position remote from the piston, in which position they are locked by the two O-rings  31  acting as detent elements. The annular shoulders  26 ,  27  and  26 ,  28  rest on one another and define the first terminal position, remote from the piston, of the sleeves  19  relative to the piston  4 . 
   In the stroke position shown in  FIG. 4 , the piston  4  has moved so far to the right compared to  FIG. 1 , as a result of suitable imposition of compressed air on the cylinder compartment  6  and venting of the cylinder compartment  7 , that the piston rod  8  has been driven almost all the way into the working cylinder, and the sleeve  19  on the right is just now coming into engagement with the O-ring  20 , forming an inhibiting means, of the receiving opening  15  of the end part  3 . This initial action of engagement is promoted by the chamfer  22  of the sleeve  19 . The sleeve  19  and the bush  11 , closed by the screw  12  and sealed off from the sleeve via the O-ring  31 , close off the receiving opening  15  via the O-ring  20  and cause a damping chamber for the piston  4  to be created. Simultaneously, the free outflow of pressure medium from the cylinder compartment  7  via the connection conduit  14  is prevented. Now, pressure medium can flow out of the cylinder compartment  7  via the damping conduits  36 ,  40 ,  35  and the adjustable damping throttle valve  33 . 
   If the piston  4 , the piston rod  8 , and a mass connected to them move at a certain speed onward in the direction of the end part  3 , then, because of the throttled outflow of the pressure medium from the cylinder compartment  7 , a pressure increase takes place in the cylinder compartment  7 , which acts counter to the motion; in other words, damping of the motion of the piston  4  upon its approach to its end position takes place. 
   In a further course of the approach to its end position, the piston  4  reaches the stroke position shown in  FIG. 5 , in which the longitudinally displaceable damping element, in the form of the sleeve  19 , has moved all the way into the receiving opening  15  and is thus plunged all the way into the end part  3 . The stop face  24  of the annular flange  23  strikes the associated end face of the end part  3 , so that the sleeve  19  is locked by positive engagement. If the rightward motion of the piston  4  is continued, the detent action of the O-ring  31  acting as a detent element is therefore overcome, so that finally, the piston  4  can reach the end position shown in  FIG. 6 , in which the entire annular flange  23  of the sleeve  19  is received in the annular groove  25  of the piston, and the piston rests with its face end on the face end of the end part  3 . 
   In this end position of the piston  4 , the sleeve  19 , over practically its entire length, is slipped onto the bush  11  and the screw  12  protrudes axially past the sleeve  19  slightly, as can be seen from  FIG. 6 . 
   From a comparison of  FIGS. 4 and 6 , the length of the damping stroke can be found: 
   The travel by the piston  4 , from the stroke position in which the damping chamber in the cylinder compartment  7  has just been formed until the end position in  FIG. 6 , is called the damping stroke  41 . If, as in principle is true of the prior art, only one unitary damping pin were connected with the piston  4 , the result would be only the damping stroke shown at  42  in  FIG. 4  (a short distance), which is determined essentially by the axial length of the sleeve  19 , calculated from the stop face  24 . Since the sleeve  19  is longitudinally displaceable on the bush  11 , the result is a telescoping action by which the damping stroke  41  is increased to almost twice the length of the aforementioned damping stroke  42 . Without such telescoping, for the same axial length of the working cylinder, only a damping stroke  42  would be possible. As indicated at the outset, particularly with large masses, a longer damping distance is better, since among other effects this contributes to a better, impact-free dissipation of the kinetic energy. 
   If the piston rod  8  moves to the left again, beginning at the end position in  FIG. 6 , then the sleeve  19  is initially pulled out of the receiving opening  15 , since via the O-ring  31  it is coupled by frictional engagement to the bush  11  and thus to the piston  4 . In the course of this outward-extending motion, however, the bead  320  runs up against the O-ring  20 , forming an inhibiting means that prevents the sleeve  19 , which has already been pulled predominantly out of the receiving opening  15 , from leaving the receiving opening  15  completely ( FIG. 7 ). In the further outward-extending motion of the piston  4 , the bush  11  is therefore pulled out of the fixedly held sleeve  19 , until the annular shoulders  26 ,  27  rest on one another and thus, if the outward-extending motion continues, the detent locking action formed by the O-ring  20  and the bead  32  is overcome. It is thus assured that the sleeve  19 , forming the displaceable damping element, will be returned to its first terminal position, remote from the position, so that in the next inward motion that occurs, it is again in the correct outset position shown in  FIG. 1 , and thus the full damping length  41  is available. 
   The end position damping has been described above in conjunction with the approach of the piston  4  to the end part  3  remote from the piston rod  8 . The conditions upon the approach of the piston to the other end part  2  are the same so that repeated explanation of that function is unnecessary. 
   The invention has been described above in conjunction with a dual-action pneumatic cylinder that operates with a piston rod  8 . In principle, it is also applicable to working cylinders without piston rods, as shown for example in  FIG. 8 . 
   Many versions of piston-rodless working cylinders are known. Examples of them are described in European Patent Disclosure EP 0 260 344 B1 and in U.S. Pat. No. 4,373,427. In such working cylinders, the pinlike damping element is often fixedly joined to the end parts of the cylinder, and upon the motion of the piston toward the end position, the damping element enters the piston. As the US patent shows, constructions that are the reverse of this have already been proposed, but that leads to correspondingly thick end parts. If the damping element is provided on the respective end part, then the space already present in the piston in these working cylinders is advantageously utilized for the pneumatic damping, and the end parts can be kept relatively short and independent of the damping length. The present invention makes it possible even in these cases to attain substantially longer damping paths without increasing the installed length of the cylinder, as can be seen from  FIG. 8 . 
   Only those parts of the working cylinder that are essential to the invention are explained and shown. The aforementioned references, the disclosures of which are incorporated herein by reference, may be consulted for the details. The tubular cylinder body  51  is closed on its ends by two end parts  52 ,  53  and surrounds a cylinder chamber, in which a piston  54  is longitudinally displaceable. The cylinder body  51  is provided with a longitudinal slit, through which a rib joined to the piston  54  leads outward to a force-transmitting element  55 . The longitudinal slit is closed by an elastic sealing tape  56 , which is in two parts and seals off the cylinder or pressure compartment  57 ,  58  from the outside on both sides of the piston  54 . Each of the two end parts  52  has a tubular bearing part  59 , which protrudes into the respective cylinder chamber  57 ,  58  and is oriented coaxially with the piston  54 . On each bearing part  59 , a sleeve  19  as in  FIGS. 1 through 7  is supported for longitudinal displacement; associated with it is a coaxial cylindrical receiving opening  15  in the diametrically opposite face end of the piston  54 . The sleeve  19  is designed and supported as shown particularly in  FIG. 3 . Identical elements are identified by the same reference numerals and need not be explained again. 
   The same is similarly true for the embodiment of the receiving opening  15 , which extends axially in the form of a blind bore into the piston  54 . The tubular bearing parts  59  in the end parts  52 ,  53  each discharge into a conduit  60 , which leads to a throttle valve  33 , similarly to that shown in  FIG. 2 . The construction and action of this valve has already described in conjunction with  FIG. 2 , so that once again a repeated explanation is unnecessary.  FIG. 8  shows the piston-rodless working cylinder in a stroke position in which the left sleeve  19 , forming a damping element, is in the outward-extended terminal position, or in other words is shown remote from the end part  52 . Once again, detent locking, or optionally, merely frictional engagement between the bearing part  59  and the displaceable sleeve  19  keeps the displaceable damping element formed by them in the outward-extended position. Upon a motion of the piston in the direction of the left end position, the sleeve  19  is first thrust into the receiving opening  15 , whereupon the sleeve itself is slipped farther in telescoping fashion on the bearing part  59  until it rests on the end part  52 . Detent locking or a simple frictional engagement between the sleeve  19  and the O-ring  20  that forms the inhibiting means assures that the sleeve  19  forming the displaceable damping element is returned to the outward-extended terminal position, shown in  FIG. 8 , upon a piston motion away from the end part  52 . 
   The invention has been described above in conjunction with throttle valve  33 , which causes the throttling of the pressure medium flowing out of the respective cylinder compartment upon the approach of the piston to an end part and thus regulates the damping. Particularly in pneumatic cylinders with a relatively long damping path, it can be expedient, instead of such a throttle valve, to provide a pressure limiting valve, of the kind known for instance from U.S. Pat. No. 3,196,753 the disclosure of which is incorporated herein by reference. The combination of a lengthened damping stroke by telescoping as described with a pressure limiting valve brings about a substantial improvement in the adjustability of the pneumatic damping. Since pressure limiting valves close below a defined, set threshold value, it is expedient in this case to proved a parallel conduit (see conduit  40  in  FIG. 2 ), by way of which the remaining air is diverted from the damping chamber to the connection conduit, so as to reach the end position of the piston quickly.