Abstract:
Disclosed is a damping device to be incorporated into fluid systems, particularly hydraulic systems, said damping device comprising an expansion hose. An essentially rigid damper which is oriented counter to the direction of flow, is disposed inside the internal space of said expansion hose. The damper pipe is provided with a completely closed wall, resulting in a good damping effect. Preferably, the damper pipe is significantly less flexible in the radial direction than the outer expansion pipe, whereby the damping effect is substantially enhanced.

Description:
RELATED APPLICATIONS 
   This application claims priority to international patent application numbers PCT/DE03/01454, filed on May 7, 2003; and DE 102 21 277.5, filed on May 14, 2002, the disclosure of which is incorporated by reference herein in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a damping device for damping vibrations and pulsations in fluid systems, specifically in hydraulic systems. 
   2. Description of the Related Art 
   Damping devices for hydraulic systems have been known, in which case, for example said devices are used for damping vibrations and pulsations caused by the drive source. Such devices are used for the reduction of sound, pulsations and pressure peaks. Such damping devices have an input and an output opening used for their insertion in a hydraulic system. The hydraulic fluid flows through said devices. 
   SUMMARY OF THE INVENTION 
   Pulsations, pressure peaks and similar pressure fluctuations occurring in hydraulic systems cover a spectrum which may also contain low-frequency components. The present invention is to solve the problem of providing a small, compact damping device which features good pulsation damping properties, in particular, also in the low-frequency range. 
   The inventive damping device comprises a damper housing, in which a damper pipe extending into the internal space is arranged counter to the direction of flow. This damper pipe has a closed wall, i.e., it does not have any bores or openings. As a result, a pressure-impervious resonator wall is created. Pressure shocks entering the internal space move as a pressure wave between the external wall of the damper housing and the damper pipe. These shocks are damped in this internal space. The shocks which reach the output connection have only a minimal effect. These shocks are reflected, as well as damped, in the annular space between the damper pipe and the wall of the damper housing. 
   The inventive damping device achieves a good damping effect, in particular, in the low-frequency range, as well as good hydraulic pulsation damping. Furthermore, the damping device is functionally safe and requires only a small space for installation. 
   The damper housing preferably is a tubular body which, in turn, preferably is configured as a cylindrical pipe. This cylindrical pipe encloses an internal space which does not have any built-in components, i.e., holders, flow elements or the like. Preferably, the damper pipe is configured as an expansion hose, i.e., the damper pipe preferably consists of an elastic or expandable material. A plastic material or an elastomer material may be used. Preferably, this material features internal damping capabilities so that incoming sound or pressure waves are at least partially damped due to dissipation. 
   The ends of the damper housing are preferably provided with connecting pieces which, for example, may be fastened to the internal wall of the expansion hose by means of annular ribs having a saw-tooth profile. Caps or sleeves, for example, pinch sleeves which extend over the damper housing, i.e., the expansion hose, secure the connecting piece so that even shock waves cannot drive this connecting piece out of the damper housing. 
   Considering a simplified design, the two connecting pieces are configured respectively in the same manner; however, they may comprise marks or other identifying symbols, or display differences, in order to be able to distinguish the input from the output of the damping device. 
   In a preferred form of embodiment at least the output-side connecting piece comprises a seat to which the damper pipe is mounted. The damper pipe extends in a self-supporting manner from this seat into the internal space of the damper housing, whereby the pipe is preferably fixed in a position concentric to the damper housing. As a result, an annular cul-de-sac is formed between the damper pipe and the damper housing, in which cul-de-sac the sound waves and the hydraulic pressure pulsations are reflected and damped. 
   The self-supporting arrangement of the damper pipe offers the advantage that reflections of the sound wave occur only at the end of said cul-de-sac. However, should this be desirable, additional elements may be located in this annular cul-de-sac in order to generate specifically targeted sound reflections. 
   The damper pipe has one open end for receiving the draining fluid which, preferably, is located opposite the input-side connecting piece, i.e., in coaxial alignment with the input-side connecting piece. This results in minimal flow resistance. A useful starting point for determining dimensions may be that the distance from the end of the damper pipe to the outlet of the input-side connecting piece into the internal space corresponds approximately to the diameter of the damper housing. 
   The damper pipe is preferably flexible, i.e., it is configured in such a manner that it can be bent slightly, whereby the pipe is as rigid as possible in radial direction. This pipe can be configured as a pipe of plastic material, preferably reinforced by a support structure. This structure may be embedded in the damper pipe. For example, the support structure may be a metal spiral, for example, a ribbon spiral coated with a plastic material, for example, PTFE. Furthermore, the plastic material may be applied by extrusion-coating or a shrink-on process. Other plastic materials which are stable with respect to the media used, and at existing temperatures, may also be provided. These plastic materials mainly serve to render the spiral-shaped ribbon structure impervious to media. Consequently, the medium can be transported only through the open end of the damper pipe which acts as a resonator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional details of advantageous forms of embodiments of the invention are provided by the drawings, the description or the subclaims. They show: 
       FIG. 1  is a simplified illustration of a sectional view, in longitudinal direction, of the inventive damping device; 
       FIG. 2  is a sectional view, in longitudinal direction, of part of the damping device of  FIG. 1 ; 
       FIG. 3  is a sectional view, in longitudinal direction, of part of a modified form of embodiment of said damping device; and 
       FIG. 4  is a simplified view, in longitudinal direction, of another modified form of embodiment of said damping device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a damping device  1  which is used for installation in a hydraulic system. In practical applications, such a damping device  1  is also referred to as a tuner or a resonator. Damping device  1 , for example, is used in a hydraulic system for pulsation and sound damping and is arranged, for example, between a hydraulic pump and a hydraulic load, for example, a hydraulic power-assisted steering system. 
   Damping device  1  comprises a damper housing  2  which, for example, is created by a section of an expansion hose. This expansion hose may be a fabric-reinforced rubber hose or the like. This hose has a given elasticity in radial direction and/or in axial direction. Damper housing  2  encloses an approximately cylindrical internal space  3  which is closed on both ends by connecting pieces  4 ,  5 . Both connecting pieces  4 ,  5  have respectively the same configuration. Connecting piece  4  forms the input connection while connecting piece  5  forms the output connection. To this end, arrows  6 ,  7  symbolize the direction of flow in which the medium flows through damping device  1 . Connecting piece  4  will be described hereinafter. The details of connecting piece  5  have the same reference numbers (with an apostrophe, to be able to make a distinction), whereby the same applies to the description. 
   Connecting piece  4  has a through bore  9  extending in a direction that is coaxial with respect to a longitudinal central axis  8  of damper housing  2 , whereby said bore  9  forms the input or output (through bore  9 ′) of damping device  1 . Connecting piece  4  comprises means for connecting a hydraulic line which are not illustrated in detail. These means may be internal or external threads or other connecting means. At the end of connecting piece  4  located in internal space  3  through bore  9  widens in a step  11  to a larger diameter which is determined by a wall  12  arranged in a cylindrical and coaxial manner relative to longitudinal central axis  8 . Step  11  and wall  12  form a seat  14  for damper pipe  15 . 
   The cylindrical external side of connecting piece  4  has one or more annular or thread-like helically arranged ribs  16 , whereby said ribs have a triangular cross-section. These ribs are used for fixing connecting piece  4  in place on the internal wall of damper housing  2 . In addition, connecting piece  4  has an annular flange  17  extending in radial direction, said flange forming an end stop when connecting piece  4  is inserted into the open end of damper housing  2 . Between flange  17  and the face end of damper housing  2 , there is a covering cap  18  which has a socket-shaped section that extends over the outside of the damper housing to approximately cover the end of connecting piece  4 . Cover plate  18  may be pressed together with damper housing  2  in order to ensure that connecting piece  4  is firmly seated. 
   Damper pipe  15  is held on one end  19  at seat  14 ′ of the output-side connecting piece  5 . To do so, end  19  is seated in the pressed seat in the internal space enclosed by wall  12 ′. Consequently, damper pipe  15  extends in a self-supporting manner into internal space  3 , whereby said pipe and the internal wall of damper housing  2  define an annular damper space  21 . This space does not contain any components or elements and hence is empty. On its face, said space is closed by a conical annular surface  22 ′ of connecting piece  5 , for example. The pitch of this annular surface  22 ′ relative to longitudinal central axis  8  is preferably 45 degrees. Therefore, this surface acts as an insertion guide when connecting piece  5  is inserted into the hose which forms damper housing  3 . 
   The length of damper pipe  15  preferably has dimensions which are such that the free open end of said pipe is at a distance from connecting piece  4 , which said distance is at most slightly greater than the internal diameter of damper housing  2 . Its passage channel  24  has the same diameter as that of through bore  9 ,  9 ′. The facing end of damper pipe  15  is configured as a flat annular surface  25 . 
   Damper pipe  15 , for example, is designed as shown by  FIG. 2 . Said damper pipe has a closed wall which is formed by a plastic element  26 . This element consists of PTFE, for example, or of another plastic material which exhibits sufficient thermal stability and is resistant to the medium flowing through damping device  1 . Plastic element  26  is stiffened in radial direction by means of a support structure  27 . This support structure is formed, for example, by a helically wound metal wire or ribbon  28 . This ribbon may be wound also in such a manner that the individual wraps continuously abut against each other. As is shown by  FIG. 2 , plastic element  26  is applied to the outside of said support structure  27 . For example, it may also be configured as a shrunk-on hose or an otherwise applied plastic coating. Due to this support structure, damper pipe  15  is rigid toward the inside, whereas the damper housing is slightly resilient toward the outside. 
   As an alternative, support structure  27  may be at least partially embedded in plastic element  26 , as shown by  FIG. 3 . In this case, individual wraps of the metal ribbon include gaps which are filled by the plastic material of plastic element  26 . In both cases, damper pipe  15  is impervious to media along its entire length and is reinforced by support structure  27  along its entire length. Considering its strength properties, said damper pipe is homogeneous. Support structure  27  is provided solely for the purpose of reinforcement. This structure protects the applied plastic pipe against collapse or compression, even in the event of pressure shocks. 
   The above-described damper device  1  works as follows: 
   During operation, medium flows through damper housing  2  in such a manner that open end  23  of damper pipe  15  opposes the arriving flow. If pressure waves enter internal space  3 , these waves enter—as one pressure wave—predominantly damper space  21  and are reflected there by annular surface  22 ′ in order to move back. In doing so, these waves are damped and, in addition, can interfere with newly entering pressure waves. Considering the transmission of pressure, damper pipe  15  is hard, i.e., pressure waves moving along damper space  21  are transmitted only minimally, or not at all, to the medium flowing through passage channel  24 . The result is an extremely effective pulsation damper which eliminates, or significantly damps, in particular, low-frequency pulsations and pressure peaks. 
     FIG. 4  shows a modified form of embodiment of damping device  1 . It largely corresponds to damping device  1  of  FIG. 1 . Therefore, using as basis the same reference numbers, reference is made to the description of the form of embodiment of  FIG. 1 . Damping device  1  of  FIG. 4  differs from the latter in that it comprises a damper element in damper space  21 . Said element may be configured, for example, as a throttle sleeve  29  which is provided at a selected location in damper space  21 . In doing so, said sleeve encloses damper pipe  15  in a concentric manner. With said sleeve, said damper pipe closes an annular gap having a radial thickness of one tenth of a millimeter, for example. Thus, said throttle sleeve divides damper space  21  into two partial damper spaces  21   a ,  21   b , which are acoustically coupled with each other by the annular gap defined with damper pipe  15 . Such a throttle sleeve  29  may be used for intensifying the damping effect, for equalizing damper device  1  and for adjusting a desired damper band width. In addition, throttle sleeve  29  also creates a certain supporting effect for damper pipe  15 . 
   Throttle sleeve  25  is protected against axial shifting in damper housing  2 , for example, by a throttle fixation sleeve  31 , which is placed on the outside of the hose. Throttle fixation sleeve  31  may be configured, for example, as a closed ring which encloses the throttle housing on the outside at the site where throttle sleeve  29  is located. Throttle fixation sleeve  31  is compressed in radial direction in order to immovably fix throttle sleeve  29  in position. 
   For installation in fluid systems, in particular hydraulic systems, a damping device is provided which comprises an expansion hose  2  containing on the inside a mostly rigid damper pipe  15  oriented counter to the direction of flow. Damper pipe  15  comprises a completely closed pipe wall which successfully enables a good damping effect. Preferably, damper pipe  15  is distinctly less flexible in radial direction than the external expansion pipe. This substantially enhances the damping effect.