Abstract:
A residual pressure valve ( 10; 10   a;    10   b ) for a flow medium, in particular for air, the flow passage ( 30 ) of which is arranged in a valve housing ( 15 ) and is designed so as to allow flows to pass in different directions and so as to be interrupted by an at least partially movable sealing element ( 41; 41   a ) depending on the pressure of the flow medium, wherein an energy store ( 45 ) which is in particular designed as a pressure spring, the sealing element ( 41; 41   a ) is seated against a counter element ( 21; 21   a ) in a sealing manner when the flow medium drops below a minimum pressure in order to interrupt the flow passage ( 30 ), and wherein the flow path ( 30 ) has two separate bores ( 32, 58 ) which are arranged coaxially in relation to one another and are connected to one another by at least one connecting channel ( 33 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a residual pressure valve. 
         [0002]    Such a residual pressure valve is known from the applicant&#39;s EP 0 987 475 B1. 
         [0003]    The known residual pressure valve which is able to allow flows to pass in different flow directions serves here for holding a particular residual pressure within a spring strut, which is acted upon by compressed air, in a motor vehicle. The residual pressure valve known from the said document has proved here to be a reliable valve in practice, which meets the requirements which are set. However, it is relatively complex in construction, in particular by the provision of several longitudinal bores constructed in longitudinal direction of the valve housing in one of the valve housing components, which bores are part of a flow passage for the flow medium. 
         [0004]    It is therefore an object of the invention to further develop a residual pressure valve such that it is able to be produced particularly simply and precisely from production-orientated considerations. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based here on the idea in particular of replacing the longitudinal bores present in the prior art, which are produced by separate, machined manufacturing steps, with an annular space which is formed automatically on joining together of the two valve housing parts through the geometry of the valve housing parts and therefore does not require any separate processing or respectively production whatsoever. 
         [0006]    Advantageous further developments of the residual pressure valve are indicated in the subclaims. All combinations of at least two of the features disclosed in the claims, the description and/or the figures fall within the scope of the invention. 
         [0007]    A particularly simple and precise producibility of the counter element, which cooperates with the sealing element in order to block the flow path for the flow medium on dropping below a particular minimum pressure, is achieved when the counter element is formed by a wall section—of the first valve housing part—which is circumferential radially to the longitudinal axis of the valve housing. 
         [0008]    In a first structural embodiment of the sealing element, provision is made here that the latter has in a recess on the side facing the wall section an O-ring which lies against the wall section in order to block the flow path. As the O-ring is a standard part, the manufacturing effort or respectively the manufacturing costs are thereby increased only relatively slightly and, moreover, it can be exchanged particularly simply in the case of failure. 
         [0009]    Alternatively to an O-ring, however, it is also possible that the sealing element has on the side facing the wall section an annular or cylindrical seal consisting of elastic material, which seal lies with an end face against a sealing edge of the wall section in order to block the flow path. In particular through the construction of the sealing edge on the wall section a particularly high sealing effect is achieved here through a relatively high surface pressure between the sealing edge and the sealing element or respectively the seal. 
         [0010]    To connect the two valve housing parts it is proposed in a first structural form that they are connected to one another by a screwed connection. Thereby, in particular a particularly simple assembly is made possible and, moreover, a disassembly of the valve housing or respectively a separating of the two valve housing parts again is possible with simple tools. 
         [0011]    In order to enable a reliable and secure sealing of the valve housing toward the exterior in the case of the provision of a screwed connection between the two valve housing parts, in which at the same time no moisture or similar whatsoever can penetrate into the valve housing, it is proposed, moreover, that at least one of the two valve housing parts has optionally a radially circumferential flange region which acts as an axial stop on connecting of the two valve housing parts by means of the screwed connection, and that in the at least one flange region an annular recess is formed to receive a seal which is constructed as an O-ring. Furthermore, the flange-shaped region is effective for simplifying assembly. 
         [0012]    In an alternative construction for the production of the connection of the two valve housing parts, it is proposed that the latter are connected to one another by a laser-welded connection. Such a connection has the particular advantage that, compared with a screwed connection, an additional sealing element (e.g. in the form of an O-ring) can be dispensed with. 
         [0013]    In order to enable the axial position of the two valve housing parts in relation to one another without additional auxiliary means or respectively assembly aids on joining together of the two valve housing parts, it is proposed, moreover, in a structurally advantageous embodiment that one of the valve housing parts has a collar which is circumferential in a flange-shaped manner, against which, on joining of the two valve housing parts, the other valve housing part lies with an end face. 
         [0014]    In a preferred manner with regard to production, this abutting region can be, at the same time, the region in which the laser-welded connection connects the two valve housing parts to one another. 
         [0015]    In order to prevent leakage air from being emitted to the environment via the guidance of the sealing element, it is proposed, moreover, in a further preferred embodiment of the invention that the sealing element is constructed in the manner of a piston, and that the sealing element has an annular groove on a circumferential surface in the region of the mount in the first valve housing part, in which annular groove a sealing element, in particular in the form of an O-ring is arranged, which lies against the mount. 
         [0016]    An embodiment is particularly preferred here in which an energy store is arranged in an energy store space which is connected with the environment by means of at least one vent bore. Thereby, it is prevented in particular that the counterforce which is able to be set by the energy store, via which the minimum pressure is set in the pressure store, is tampered with by inflowing air or respectively inflowing flow medium into the receiving space for the energy store. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Further advantages, features and details of the invention will emerge from the following description of particularly preferred example embodiments and by means of the drawings. 
           [0018]    These show in: 
           [0019]      FIG. 1  a partial longitudinal section through the upper part of a spring strut, acted upon by compressed air and containing a residual pressure valve, in a motor vehicle, 
           [0020]      FIG. 2  and  FIG. 3  a first example embodiment of the residual pressure valve according to the invention in different angular positions in side view respectively partially in section, 
           [0021]      FIG. 4  a second residual pressure valve, modified with respect to  FIGS. 2 and 3 , in a side view partially in section and 
           [0022]      FIG. 5  a third residual pressure valve, modified with respect to  FIGS. 2 to 4 , in a side view partially in section. 
       
    
    
       [0023]    Identical components or respectively components with an identical function are provided with identical reference numbers in the figures. 
       DETAILED DESCRIPTION 
       [0024]    In a spring strut  100 , acted upon by compressed air, illustrated only with its upper region in  FIG. 1 , for a motor vehicle, a funnel-like mounting  105  for a residual pressure valve  10  (which is also designated as residual pressure retention valve) is fixed at an apex opening  101  in the region  102 . The residual pressure valve  10  is arranged with a screw neck  12  in a shaft-like opening  106  in the mounting  105 . An in particular specific minimum residual pressure is to be guaranteed by the residual pressure valve  10  in a head space  108  of the spring strut  100 . When this minimum residual pressure is reached, for example a pressure of 4 bar, the residual pressure valve  10  closes and therefore seals off the head space  108 . 
         [0025]    In  FIGS. 2 and 3  the residual pressure valve  10  is illustrated in further detail in a first embodiment of the invention. The residual pressure valve  10  has a valve housing  15  which consists of two valve housing parts  16 ,  17  which are connected to one another. The first valve housing part  16 , on which also the screw neck  12  is constructed, is constructed substantially in a sleeve shape and has a region  18  with the screw neck  12 , which has a smaller diameter with respect to a region  19  of the valve housing part  16 . The two regions  18 ,  19  are connected to one another by means of an annular wall section  21  arranged substantially perpendicularly to the longitudinal axis  20  of the residual pressure valve  10 . At the end of the screw neck  12  facing away from the head space  108  in addition a sealing ring  22  is received in an annular groove in the transition region between the two regions  18 ,  19 , which sealing ring seals toward the environment the residual pressure valve  10  which is screwed in the opening  106 . 
         [0026]    The second valve housing part  17  is likewise constructed approximately in a sleeve shape and projects with a section  24  into the region  19  of the first valve housing part  16 . The section  24  has here a first region  26 , the external diameter of which is smaller than the internal diameter of the region  19  of the first valve housing part  16 , so that an annular space  28  is formed between the two regions  19  and  26 , which is part of a flow path  30  for the flow medium, in particular for the air which is situated in the head space  108 . The one end side  29  facing the region  18  of the first valve housing part  16  is arranged spaced apart axially with respect to the wall section  21  of the first valve housing part  16 . 
         [0027]    On the side of the second valve housing part  17  facing away from the screw neck  12  of the first valve housing part  16 , said second valve housing part has a blind bore  32  consisting of several bore sections of different diameter. Preferably several connecting channels in the form of transverse bores  33 , arranged at regular angular distances from one another, originate from the blind bore  32 , of which only one transverse bore  33  can be seen in the figures. The transverse bore  33  opens out into the annular space  28  on the side facing away from the blind bore  32  and is also part of the flow path  30 . The blind bore  32  is connected in particular via a threaded connection with a source of compressed air, preferably a compressed air compressor, via which the head space  108  of the spring strut  100  is acted upon with compressed air when the residual pressure valve  10  is opened. 
         [0028]    In addition to the first region  26 , the second valve housing part  17  has in section  24  a second region  34 , the external diameter of which is enlarged with respect to the first region  26 . In particular, the external diameter of the second region  34  corresponds substantially to the internal diameter of the region  19  of the first valve housing part  16 , so that on axial joining together of the two valve housing parts  16 ,  17  the second valve housing part  17  is centred via the second region  34  to the first valve housing part  16 . The second valve housing part  17  has in addition a circumferential collar  35  in the manner of a flange, which acts as an axial stop on joining together of the two valve housing parts  16 ,  17 , as soon as the collar  35  lies against the end face  36  of the first valve housing part  16  which lies opposite the screw neck  12 . 
         [0029]    In order to connect the two valve housing parts  16 ,  17  to one another undetachably and, at the same time, in order to seal them, a welded connection with a radially circumferential weld seam  38  is formed in the transition region between the collar  35  and the end face  36 , which weld seam is preferably formed by means of a laser beam device. 
         [0030]    On the side lying opposite the blind bore  32 , the second valve housing part  17  has a mount  40  for the sliding guidance of a sealing element  41  which is constructed in the manner of a piston. Here the sealing element  41 , which is arranged so as to be movable along the longitudinal axis  20  of the residual pressure valve  10 , has within the mount  40  an annular groove  42  constructed on its outer circumference, in which annular groove an O-ring  43  is arranged, which lies against the inner wall of the mount  40 . Within the mount  40 , furthermore, a pressure spring  45  is arranged which acts as an energy store, wherein the desired residual pressure of the residual pressure valve  10  is set via the geometry of the pressure spring  45  (length, diameter, spring stiffness etc.). The pressure spring  45  rests between the bottom  46  of the mount  40  and the base  47  of the cup-shaped sealing element  41 , wherein a pin-like extension  48  of the second valve housing part  17  serves as a guide for the pressure spring  45 . 
         [0031]    As can be seen in particular by means of  FIG. 2 , at least one vent bore  49 , which is funnel-shaped in the example embodiment, running in longitudinal direction, originates from the bottom  46  of the mount  40  in a radially outer region, in the flow path of which vent bore, situated in connection with the environment, in addition an O-ring  50  is arranged as a protective element against the penetration of dirt, moisture or similar into the mount  40 , said O-ring being received in a recess  51  of the second valve housing part  17 . 
         [0032]    In the example embodiment illustrated in  FIGS. 2 and 3 , the piston base  53  of the sealing element  41  has on the side facing the screw neck  12  a round or respectively plate-shaped seal  55 , which is constructed so as to be elastic or respectively consists of an elastic material. In the position of the sealing element  41  illustrated in  FIGS. 2 and 3 , the sealing element  41  is illustrated in a position in which it blocks the flow path  30 . Here, the seal  55  cooperates with a radially circumferential sealing edge  56  which is constructed on the wall section  21  on the side facing the seal  55 . Thereby, the desired (minimum) residual pressure is maintained in the head space  108  of the spring strut  100 . 
         [0033]    If, on the other hand, the residual pressure valve  10  or respectively its sealing element  41  is situated in a position in which the flow path  30  is freed, the seal  55  is arranged spaced apart axially from the sealing edge  56 . Thereby, the compressed air situated in the head space  108  can arrive via the bore  58  constructed in the region of the screw neck  12  in the first valve housing part  16  and via the space between the wall section  21  and the seal  55  into the annular space  28 , and from there via the transverse bores  33  into the blind bore  32  and the environment. Furthermore, with opened residual pressure valve  10  the head space  108  of the spring strut  100  can be filled with compressed air via the compressed air source (not illustrated). For this, the sealing element  41  or respectively the seal  55  is raised from its seal seat, contrary to the elastic force of the pressure spring  45 , by the inflowing compressed air. The residual pressure valve  10  is therefore able to be flowed through in two directions over the flow path  30 , and only forms a barrier in the case of falling below the residual pressure which is set via the pressure spring  45 . 
         [0034]    In  FIG. 4  a modified embodiment of the invention is illustrated with a residual pressure valve  10   a . The residual pressure valve  10   a  differs from the residual pressure valve  10  in the region of its sealing element  41   a . Here, the sealing element  41   a  has a piston base  53   a  constructed in a stepped manner, in which an O-ring  60  is arranged in a radially circumferential mount  59 , which O-ring is seated in a sealing manner against the wall section  21   a  of the valve housing  16   a  in the blocking position of the residual pressure valve  10   a . If applicable, provision can be made here that the one end side  61  of the piston base  53   a  is likewise situated in abutting contact with the wall section  21   a . It is also essential that the wall section  21   a , in contrast to the wall section  21 , has no sealing edge  56  as in the residual pressure valve  10 . 
         [0035]    In  FIG. 5  a residual valve  10   b , which has once again been modified, is illustrated, which differs from the residual pressure valve  10   a  in that the two valve housing parts  16   b ,  17   b  are connected to one another by means of a screwed connection  65 . Here, the second valve housing part  17   b  has a collar  66 , circumferential in a flange-shaped manner, acting as axial stop, which collar carries on the side facing the first valve housing part  16   b  an O-ring  68  in an annular mount  67 , which O-ring seals the screwed connection  65  toward the exterior on screwing of the two valve housing parts  16   b ,  17   b . Of course, it is also possible to dispense with the O-ring  68  and to construct a seal for example by introducing an adhesive or a sealing material in the region of the screwed connection. 
         [0036]    The residual pressure valves  10 ,  10   a  and  10   b  so far described can be altered or respectively modified in a variety of ways without departing from the idea of the invention.