Abstract:
Disclosed is a check valve ( 5 ) that is screwed into a threaded bore ( 1 ) of a housing ( 2 ) of a hydraulic subassembly between a first pressure side ( 26 ) and a second pressure side ( 27 ) by means of an external thread ( 11 ) which is disposed in a first cylinder section ( 8 ) of a cylindrical valve housing ( 6 ) of the check valve ( 5 ). A passage duct ( 39 ) which allows a hydraulic fluid to flow between the sidewall of the threaded bore ( 1 ) and a first removed portion ( 16 ) of the surface area ( 10 ) of the cylindrical valve housing ( 6 ) is embodied in at least one angular segment (a 1 , a 2 , and a 3 ) of the valve housing ( 6 ).

Description:
The invention relates to a nonreturn valve which can be screwed into a hydraulic fluid-conveying pressure line having a thread. 
   Comparatively simple and secure fastening of a nonreturn valve in a pressure line is obtained by means of a screwed connection. For this purpose, the nonreturn valve is fitted by its external thread provided on the valve housing into the internal thread formed in the pressure line. 
   The screwed connection produces both a form-fitting and force-fitting connection between the nonreturn valve and the pressure line. Additional sealing by means of sealing rings (e.g. O-rings) can be dispensed with in this case. Mounting and demounting also proves to be comparatively simple. Additional components such as, for example, screws are not necessary to fasten the nonreturn valve in the pressure line. By forming suitable engagement surfaces on the nonreturn valve which correspond to the standard dimensions of screwing tools, the nonreturn valve can be fastened in the pressure line and also removed again relatively simply using a standard screwing tool. 
   The constructional requirements of a screw-in nonreturn valve are, in particular, a compact construction of the nonreturn valve in the axial and radial direction, while allowing for a flow cross-section as large as possible for the operating state in which the nonreturn valve is open. Even the formation of the external thread on the valve housing requires a certain additional constructional volume in the overall volume of the nonreturn valve, which either leads to an increase in the overall volume of the nonreturn valve in the radial direction and possibly also in the axial direction or which unnecessarily reduces the space still available for forming the flow duct and hence the flow cross-section inside the nonreturn valve. 
   BACKGROUND 
   DE 24 49 443 A1 describes a screw-in nonreturn valve, the valve housing of which takes up a comparatively large space in the radial direction. This is due to the fact that the diameter of the valve housing is composed in the least favourable case, owing to the arrangement of the individual functional units, of the cross-sections of the external thread, the valve housing portion of the valve housing, the valve body and the flow duct between the valve housing portion and the valve body, which are each suitably dimensioned in accordance with their function. 
   In the axial direction, too, the nonreturn valve of DE 24 49 443 A1 has a comparatively large extent. The comparatively large axial extent results from the addition of the geometry of the axially arranged functional units of the valve seat body, the valve body and the tension spring, as well as an additional space for a screwing tool which engages in each case on the inner surfaces of the valve housing for the screwing of the nonreturn valve. 
   SUMMARY OF THE INVENTION 
   The object on which the invention is based, therefore, is to develop the nonreturn valve having the features according to the precharacterising clause of claim  1  in such a way that, through a novel constructional arrangement and geometrical configuration of the individual functional units required for a nonreturn valve, a very compact construction of the nonreturn valve in the radial and axial direction is achieved, while at the same time allowing for a sufficiently large flow cross-section of the flow duct, and to increase the functional reliability the spring is not arranged in the flow region. 
   The object of the invention is achieved by a nonreturn valve having the features of claim  1 . 
   According to claim  1 , by forming a passage duct by removal of material from the lateral surface of the valve housing for the hydraulic fluid flow, the flow duct is transferred to the constructional space of the external thread and furthermore partly to the valve-housing constructional space situated inside the external thread. Thus, no additional constructional space has to be provided for the flow duct in the radial direction of the valve housing, which markedly reduces the extent of the nonreturn valve in the radial direction. 
   Advantageous refinements of the invention are specified in the dependent claims. 
   By realising the flow duct, according to claim  2 , using three passage ducts distributed uniformly on the lateral surface of the valve housing, the flow duct cross-section is additionally increased and a flow profile is produced inside the nonreturn valve which approximates the laminar flow in the pressure-line region upstream and downstream of the nonreturn valve. 
   The external thread on the valve housing extends over only a limited cylindrical portion of the hollow-cylindrical valve housing. Therefore, sufficient free space is available at the outer lateral surface of the valve housing to form engagement surfaces for a screwing tool for screwing the nonreturn valve into the internal thread of the pressure line. These engagement surfaces, which are likewise produced by removal of material from the lateral surface of the valve housing, are formed on the valve housing in the axial direction at the level of the spring or spring plate and do not therefore require any additional axial extension of the valve housing of the nonreturn valve, as in the case of the engagement surfaces in the nonreturn valve of DE 24 49 443 A1. 
   Thus, by constructionally redesigning the nonreturn valve, a valve housing is realised which is compact in the axial as well as radial direction and has a flow duct with sufficiently large flow cross-section and a quasi-laminar flow profile. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention is illustrated in the drawing and described in more detail below. In the drawing: 
       FIG. 1  shows a cross-sectional illustration of a pressure line system having a nonreturn valve according to the invention, screwed into a threaded bore; 
       FIG. 2  shows a three-dimensional illustration of a nonreturn valve according to the invention, and 
       FIG. 3  shows a cross-section of a nonreturn valve according to the invention. 
   

   The nonreturn valve according to the invention is described below with reference to  FIG. 1  to  FIG. 3 . 
   DETAILED DESCRIPTION 
   The threaded bore  1 , which is situated according to  FIG. 1  in the housing  2  of a hydraulic assembly, for example an axial piston machine, has an internal thread  12 . The threaded bore  1  continues at its deepest end-point in a continuation bore  3 , the inside diameter of which is designed smaller than the inside diameter of the threaded bore  1 . The transition  4  between the threaded bore  1  and the continuation bore  3  has a conical form. 
   The nonreturn valve  5  has a primarily cylindrical valve housing  6 . Approximately in the middle third of the valve housing  6 —when the valve housing  6  is viewed in the axial direction—the valve housing  6  has a primarily radially oriented enlargement  7 . This primarily radially oriented enlargement  7  is subdivided into a first cylindrical portion  8  and a second cylindrical portion  9 , each of approximately half its axial extent. While the outside diameter of the first cylindrical portion  8  corresponds to the inside diameter of the threaded bore  1 , the outside diameter of the second cylindrical portion  9  is less prominent. 
   The first cylindrical portion  8  has on its outer lateral surface  10  an external thread  11  which is screwed into the internal thread  12  of the threaded bore  1 . The internal thread  12  here is cut into the threaded bore  1  to such an extent that, when the nonreturn valve  5  is fully screwed into the threaded bore  1 , the valve housing  6  of the nonreturn valve  5  is pressed, by its bevelled edge  15  situated between the front end face  13  and the cylindrical lateral surface  14 , against the conical transition  4  between threaded bore  1  and continuation bore  4 . Owing to this form-fitting contact between the valve housing  6  and the conical transition  4 , the hydraulic fluid is prevented from flowing between the valve housing  6  and the conical transition  4 . 
   In the first cylindrical portion  8 , first regions of material removal  16  are provided at the outer lateral surface  10  in two, three or four equal-sized angular segments α 1 , α 2 , α 3  and α 4  (in  FIG. 2  the embodiment is illustrated with three equal-sized angular segments α 1 , α 2  and α 3 , the angular segment α 3  not being visible in  FIG. 2  owing to the perspective illustration) which are arranged at equal-sized angular distances with respect to one another, the regions of material removal  16  resulting in a levelling of the cylindrical lateral surface  10  in the angular segments α 1 , α 2 , α 3  and α 4 . Each first region of material removal  16  thus forms a throughflow duct  39  for a hydraulic fluid flow between the lateral surface of the threaded bore  1  and the surface of the region of material removal  16  of the valve housing  6 . 
   The first regions of material removal  16  in the angular segments α 1 , α 2 , α 3  and α 4  are continued in the same order of magnitude in the second cylindrical portion  9 . Second regions of material removal  17 , which are designed in the same order of magnitude as the first regions of material removal  16 , are provided in the cylindrical portion  9  in the equal-sized angular segments α 5 , α 6 , α 7  and α 8  situated between the angular segments α 1 , α 2 , α 3  and α 4  (in  FIG. 2  only the embodiment with three angular segments α 5 , α 6  and α 7  is illustrated, the angular segments α 6 , α 7  not being visible in  FIG. 2  owing to the perspective illustration). The cross-sectional profile of the second cylindrical portion  9  thus has a hexagonal profile. Since the areas of these regions of material removal  16  correspond to a standard size for the use of a square, hexagonal or octagonal screwing tool, they can be used as engagement surfaces for a square, hexagonal or octagonal screwing tool for screwing the nonreturn valve  5  into the threaded bore  1 . 
   The primarily cylindrical valve housing  6  in the nonreturn valve  5  has an axially directed cutout  18  which, in a first portion  19  situated at the end of the valve housing  6  facing towards the continuation bore  3 , has a smaller inside diameter than in a second portion  20  situated at the end of the valve housing  6  situated in the region of the threaded bore  1 . The conical transition  40  between the smaller inside diameter of the first portion  19  and the larger inside diameter of the second portion  20  of the cutout  18  serves as a valve seat  21 . 
   A spherical valve body  22  situated in the second portion  20  is pressed against the valve seat  21 . The force required to press the valve body  22  against the valve seat  21  is produced to a certain degree by the spring force of a spring  25  prestressed between a first spring plate  23  and a second spring plate  24 . The transmission of the spring force of the prestressed spring  25  to the valve body  22  takes place via the first spring plate  23 . A further part of the force required to press the valve body  22  against the valve seat  21  is created via the pressure difference between the first pressure side and the second pressure side  27 . 
   To allow the pressure difference between the first pressure side  26  and the second pressure side  27  to act on the valve body  22 , the valve housing  6  has a first inflow opening  28  at its end face  13  facing towards the first pressure side  26 —towards the continuation bore  3 . The pressure acting in the first pressure side  26  arrives, via the first inflow opening  28 , at the surface portion (broken line in  FIG. 3 ), situated within the first portion  19 , of the valve body  22 . 
   The second valve plate  24  is supported on a snap ring  34  which is fitted in an annular groove at the lateral surface of the cutout  18  in the region of a second opening  31  situated at an end face  30 , facing towards the second pressure side  37 , of the valve housing  6 . To enable it to be supported on the snap ring  34 , the primarily cylindrical second spring plate  24 , which is designed structurally identically to the first spring plate  23  with a view to using as many identical parts as possible in an assembly, has at the edge between the lateral surface and the lower end face a notch  35 , which also increases the functional safeguarding of the loaded snap ring against falling out of the groove. To fix the spring  25 , the first and second spring plate  23  and  24  has at the edge between the lateral surface and the upper end face an annular notch  36 . The spring plate  23  and  24  has a conical transition  29  from the lower end face to the inner bore  32 . If the component is used as the first spring plate  23 , the conical transition  29  serves as a supporting surface of the first spring plate  23  with respect to the spherical valve body  22 . 
   In the second portion  20  of the cutout  18  of the valve housing  6 , a plurality of through-openings  38  are provided in the region of the valve body  22 , on a circular line which is concentric with the longitudinal axis  37  of the valve housing  6  and lies on the inner lateral surface of the valve housing  6 , these through-openings being distributed in equidistant angular segments β and opening into a region  39  situated between the valve housing  6  and the side wall of the threaded bore  1  on the side of the first cylindrical portion  8  facing towards the first pressure side  26 . 
   If the pressure of the hydraulic fluid in the first pressure side  26 —in the continuation bore  3 —is greater than the counterpressure composed of the pressure of the hydraulic fluid in the second pressure side  27 —in the threaded bore  1 —and the pressure of the spring force of the prestressed spring  25 , the valve body  22  lifts off from its valve seat  21  and enables the hydraulic fluid to flow from the first pressure side  26 —in the continuation bore  3 —via a flow duct between the valve body  22  and the conical transition  40  of the valve housing  6  and via the through-bores  38  to the region  39  in the threaded bore  1 . From the region  39  of the threaded bore  1 , the hydraulic fluid flows via three passage ducts  39 , formed by regions of material removal  16  of the first cylindrical portion  8  of the valve housing  6 , into the threaded bore  1 . The valve seat separates the first pressure side  26  from the second pressure side  27 .