Abstract:
Pneumatic control valve of a compressed-air brake system of a vehicle, having at least one first valve system which is arranged in an upper housing and has a first valve piston which interacts with a first valve and can be actuated manually or by means of an actuator via a spring element by means of a plunger piston, having a second valve system which is arranged in a lower housing with a coaxially arranged second valve piston which can be actuated pneumatically and/or mechanically by the first valve system and with a second annular plate valve, The first valve piston is guided via the plunger piston in the cylindrical guide in the housing upper part.

Description:
[0001]    The invention relates to a pneumatic control valve, in particular a dual-circuit brake transducer in a compressed-air brake system of a vehicle for correcting a brake pressure which corresponds to a desired braking action, having at least one first valve system which is arranged in a housing upper part and has a first valve piston which interacts with a first annular plate valve and can be actuated manually or by means of an actuator via a spring element by means of a plunger piston, having a second valve system which is arranged in a housing lower part with a coaxially arranged second valve piston which can be actuated pneumatically and/or mechanically by the first valve system and with a second annular plate valve which interacts therewith, the plunger piston having, centrally an axial cylindrical projection, by means of which the plunger piston is guided in cylindrical guides in the region of the housing upper part and in the region of the housing lower part. 
       BACKGROUND OF THE INVENTION 
       [0002]    A pneumatic control valve of this type is known from GB 2 158 534 A. In the case of the said control valve, the plunger piston is of axially very short configuration, and a coaxially extending skirt is screwed on at its end which points into the control valve. The said skirt reaches as far as a cylindrical guide which is a constituent part of a venting plate which is fastened by means of screws to the housing lower part. The plunger piston has a lip seal radially on the outside and is guided in a metallic cap of the control valve with great play in the region of the housing upper part only by means of the lip seal. Accordingly, tilting moments and transverse forces which are caused by the actuation of the plunger piston act directly on the lip seal thereof which, as a result, is subjected to increased wear with impairment of the sealing action. The skirt which is fastened to the plunger piston is guided axially through the first valve piston with great play and in a sealed manner, and does not serve to guide the first valve piston. The first valve piston is guided in the hollow-cylindrical housing upper part in an axial region with radially recessed diameters over a great axial length, the first valve piston being sealed radially on the outside with respect to the inner wall of the housing upper part by two O-ring seals which are spaced apart axially. As a result of this design, no transverse forces and tilting moments act on the first valve piston, but this known pneumatic control valve is comparatively long, since the plunger piston is guided in the cap which is screwed onto the housing upper part. In addition, the recessed bore in the housing upper part, which recessed bore serves as a guide for the first valve piston, requires complicated machining of the said housing upper part. 
         [0003]    Against this background, the invention is based on the object of proposing a comparatively short pneumatic control valve which requires a reduced outlay on machining, consists of comparatively few individual parts and is insusceptible to tilting moments and transverse forces which act on the plunger piston of the pneumatic control valve. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    This object is achieved by a pneumatic control valve having the features of claim  1 , whereas advantageous developments are defined in the subclaims. 
         [0005]    The invention accordingly relates to a pneumatic control valve, in particular a dual-circuit brake transducer in a compressed-air brake system of a vehicle for correcting a brake pressure which corresponds to a desired braking action, having at least one first valve system which is arranged in a housing upper part and has a first valve piston which interacts with a first annular plate valve and can be actuated manually or by means of an actuator via a spring element by means of a plunger piston, having a second valve system which is arranged in a housing lower part with a coaxially arranged second valve piston which can be actuated pneumatically and/or mechanically by the first valve system and with a second annular plate valve which interacts therewith, the plunger piston having, radially on the inside, an axial cylindrical projection, by means of which the plunger piston is guided in cylindrical guides in the region of the housing upper part and in the region of the housing lower part. In order to achieve the addressed object, moreover, it is provided in the said control valve that the first valve piston is guided via the plunger piston in the cylindrical guide in the housing upper part. 
         [0006]    The first valve piston is therefore not guided directly in a cylindrical guide of the housing upper part, but rather is arranged therein with increased play, with the result that, instead of being provided with one or more O-ring seals, the first valve piston manages with only one lip seal, without the sealing action and the service life of the lip seal being impaired by tilting moments and transverse forces which act on the plunger piston. Transverse forces in this regard are namely already dissipated via the plunger piston to the housing upper part. 
         [0007]    It is provided according to one preferred embodiment that, in order to guide the first valve piston, a cylindrical region of the plunger piston is arranged axially displaceably with a sliding fit in a first cylindrical bore in the first valve piston, the said first cylindrical bore preferably being arranged in a hollow-cylindrical axial projection of the first valve piston. 
         [0008]    A second guide for the first valve piston can be formed by virtue of the fact that a radially inwardly directed head-shaped protrusion with a second cylindrical bore is arranged on the hollow-cylindrical axial projection of the first valve piston, in which second cylindrical bore a first cylindrical projection of the plunger piston is arranged axially displaceably with a sliding fit. 
         [0009]    Furthermore, it can be provided that the plunger piston is formed integrally with the first cylindrical projection and a second cylindrical projection which forms an extension of the first cylindrical projection, and that the second cylindrical projection is guided axially displaceably with a sliding fit in the cylindrical guide which is arranged on the housing lower part. 
         [0010]    Moreover, it is preferably provided that the plunger piston is connected centrally and without play to a circular pressure plate which has a hollow-cylindrical projection radially on the outside, is arranged in the housing upper part, and is guided axially displaceably with a sliding fit in the housing upper part by means of the hollow-cylindrical projection including plunger piston. 
         [0011]    As a result of the proposed construction of the control valve, the plunger piston is guided twice over a great axial distance, namely with the cylindrical region of the plunger piston via the hollow-cylindrical projection of the pressure plate in the housing upper part and with the second cylindrical projection of the plunger piston in the cylindrical guide on the housing lower part. As a result, actuation-induced transverse forces and tilting moments act only slightly on the movement of the plunger piston, which are accordingly also not transmitted to the first valve piston which is after all guided with a sliding fit on the plunger piston and is sealed with respect to the cylindrical guide in the housing upper part by the lip seal. 
         [0012]    The use of the pneumatic control valve according to the invention in a compressed-air brake system of a vehicle is very advantageous. The vehicle is, for example, a commercial vehicle, for instance a lorry. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    In the following text, the invention will be explained further using an exemplary embodiment which is shown in an appended drawing. The single figure shows a diagrammatic longitudinal section through a control valve  1  which is configured according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The method of operation of the control valve  1  which is shown is substantially consistent with the method of operation of the control valves which are shown and described in GB 2 181 803 A and in DE 33 43 172 C2. The method of operation is not part of the present invention and is therefore also not described in detail, but the contents of GB 2 181 803 A and DE 33 43 172 C2 are made the subject matter of the disclosure here in their entirety. 
         [0015]    The control valve  1  has a housing consisting of a housing upper part  2  and a housing lower part  3  which are joined together in a sealed manner with a sealing ring  29  positioned in between. A plunger piston  4  is inserted centrally into a pressure plate  5  substantially without play, preferably with a press fit, and is guided axially displaceably with a sliding fit in a cylindrical guide  2   a  in the housing upper part  2  by means of a hollow-cylindrical projection  5   a  which is formed radially on the outside of the pressure plate  5 , and is secured against falling out of the housing upper part  2  by a securing ring  7  which is arranged in a circumferential groove  6  in the housing upper part  2 . The housing upper part  2  is sealed to the outside by means of a folding bellows  8 . 
         [0016]    An elastomer spring element  9  of frustoconical configuration is arranged between the pressure plate  5  and a first valve piston  10 . The elastomer spring element  9  is supported with its larger diameter region  9   d  radially inside the hollow-cylindrical projection  5   a  on the pressure plate  5  and with its smaller diameter region  9   c  on the first valve piston  10 . The elastomer spring element  9  is moulded integrally on the first valve piston  10  outside its frustoconical region and engages around and engages over the first valve piston  10  there. In this connecting region, a radially outwardly directed sealing lip  9   a  is formed on the composite component consisting of elastomer spring element  9  and first valve piston  10 . Furthermore, the first valve piston  10  is provided with an undercut annular groove  10   a  on its side which faces the pressure plate  5 , into which annular groove  10   a  an annular axial protrusion  9   b  of the elastomer spring element  9  engages. As a result of this construction, the first valve piston  10  can be arranged in the housing upper part  2  with abundant radial play, without impairing the sealing action by way of the sealing lip  9   a.    
         [0017]    In order to form the said composite component, the elastomer spring element  9  is preferably moulded onto the valve piston  10  in a mould which receives the first valve piston  10 . In order to ensure secure adhesion of the elastomer spring element  9  on the first valve piston  10 , those surface regions of the first valve piston  10  which come into contact with the elastomer spring element  9  during moulding are coated with an adhesion promoter. 
         [0018]    The frustoconical region of the elastomer spring element  9  is preferably composed of an elastomer with a greater Shore hardness than that region, on which the sealing lip  9   a  is formed, it being possible for the elastomer spring element  9  to be moulded 
         [0000]    onto the first valve piston  10  by way of a two-component injection-moulding method. 
         [0019]    The first valve piston  10  has a hollow-cylindrical axial projection  12  which points away from the pressure plate  5  and ends at an annular sealing seat  13 . The plunger piston  4  is first of all guided with a cylindrical region  4   c  with a sliding fit in a first cylindrical bore  10   b  in the first valve piston  10 , and is then guided by means of a first cylindrical projection  4   a  of the plunger piston  4  in a second cylindrical bore  10   c  which is formed in a circumferential, head-shaped radial protrusion  11  on the first valve piston  10 . 
         [0020]    A securing ring  19  which is arranged in a groove of the first cylindrical projection  4   a  of the plunger piston  4  holds the arrangement comprising the plunger piston  4 , the pressure plate  5 , the elastomer spring element  9  and the first valve piston  10  together as a structural unit which can be pre-assembled, with a predefined prestress which is applied by the elastomer spring element  9 . 
         [0021]    The first valve piston  10  interacts in a known manner by way of its annular sealing seat  13  on its hollow-cylindrical projection  12  with a first annular plate valve  14 . The first annular plate valve  14  has a radial sealing face  15  which for its part interacts in a known manner with a first non-displaceable sealing seat  16  in the housing upper part  2 . The first annular plate valve  14  is guided with a hollow-cylindrical projection  14   a  radially inside a second valve piston  30 , such that it can be displaced axially over a small travel, and is sealed with respect to the second valve piston  30  by means of a sealing ring  31 . 
         [0022]    The first annular plate valve  14  is surrounded by a first pressure space  17  which is fed compressed air from a compressed-air source in a manner which is known but not shown. The first annular plate valve  14  is pierced, as a result of which a venting passage is formed. 
         [0023]    A back-pressure spring  20  is supported axially on the housing upper part  2  and on the underside, remote from the pressure plate, of the first valve piston  10  and ensures that the arrangement comprising the plunger piston  4 , the pressure plate  5 , the elastomer spring element  9  and the first valve piston  10  bears axially against the upper securing ring  7  when the plunger piston  4  is not actuated. 
         [0024]    A compression spring  21  which is arranged in the first pressure space  17  is supported axially at one end on the first annular plate valve  14  and at the other end on a lip seal  24  which is arranged in the housing upper part  2  and is secured axially against falling out by a securing ring  25 . The said securing ring  25  is arranged in a groove in the housing upper part  2 . 
         [0025]    A brake pressure space  22  for a first brake circuit (not shown) is formed between the first valve piston  10  and the first non-displaceable sealing seat  16 , in which brake pressure space  22  a modulated brake pressure is built up by the interaction of the plunger piston  4  with the first valve piston  10  and the first annular plate valve  14 . 
         [0026]    A supporting element  23  is arranged axially displaceably on the first cylindrical projection  4   a  of the plunger piston  4  and bears against the underside of the head-shaped radial protrusion  11  of the first valve piston  10  under the axial application of force of a compression spring  26 . The said compression spring  26  is supported with its other end on a supporting disc  27  which bears against a step between the first cylindrical projection  4   a  and a second cylindrical projection  4   b  of smaller diameter of the plunger piston  4 . The supporting disc  27  is fixed on the said step by means of a securing ring  28 . The supporting disc  27  comprises a number of perforations  27   a  or perforated holes to facilitate exhaust air flow during brake release. 
         [0027]    The second valve piston  30  is guided axially in the housing lower part  3  such that it is sealed via two O-sealing rings  32 ,  33 , and interacts by way of an annular sealing seat  34  with a second annular plate valve  37 . A radial sealing face  38  of the second annular plate valve  37  interacts in a known way both with the annular sealing seat  34  on the second valve piston  30  and with a second, non-displaceable sealing seat  35  on a hollow-cylindrical projection  36  of the housing lower part  3 , which hollow-cylindrical projection  36  protrudes axially to the inside with its free end. The said hollow-cylindrical projection  36  of the housing lower part  3  is surrounded radially on the outside by an annular brake pressure space  39  which is connected to a second brake circuit (not shown), in order to feed a modulated brake pressure to the said second brake circuit. 
         [0028]    A second pressure space  17   a  which is fed compressed air from a compressed-air source in a manner which is not shown is formed between a hollow-cylindrical projection  37   a  of the second annular plate valve  37  and the hollow-cylindrical projection  36  of the housing lower part  3 . The said second pressure space  17   a  can be flow-connected in a manner which is not shown to the first pressure space  17  in the region of the first annular plate valve  14 . 
         [0029]    A compression spring  40  is arranged in the second pressure space  17   a,  which compression spring  40  is supported at one end on the second annular plate valve  37  and at the other end on a lip seal  41  which for its part is secured by a supporting ring  42 . The supporting ring  42  is secured against falling out by a securing ring  43  and is connected via radially inwardly protruding radial spokes  42   a  to a hollow-cylindrical guide  42   b  which serves to guide the second cylindrical projection  4   b  of the plunger piston  4 , with the result that the said plunger piston  4  is guided over a great length firstly by means of the pressure plate  5 ,  5   a  in the housing upper part  2  and by means of the hollow-cylindrical guide  42   b  in the housing lower part  3 . 
         [0030]    It can be seen that, as a result of the guidance of the plunger piston  4  in the housing upper part  2  by means of the hollow-cylindrical projection  5   a  of the pressure plate  5  and by means of the second cylindrical projection  4   b  in the cylindrical guide  42   b  in the housing lower part  3 , all transverse forces and tilting moments are guided directly into the housing upper part  2  and the housing lower part  3  and are kept away from the first valve piston  10 . The first valve piston  10  is guided securely on the plunger piston  4  and on its first cylindrical projection  4   a,  with the result that no excessive loading of the sealing lip  9   a  on the first valve piston  10  and a resulting reduction in the sealing action occur. 
         [0031]    The control valve  1  is ventilated in a known way by the venting passage and a venting cap  44  on the housing lower part  3  when the brake pressure in the brake pressure spaces  22  and  39  is reduced or neutralized completely by retraction of the plunger piston  4 . 
         [0032]    The control valve  1  according to the invention is of very compact construction and, with regard to the sealing action of the first valve piston  10  by way of the sealing lip  9   a,  is insusceptible to tilting moments and transverse forces which act on the plunger piston  4 . 
         [0033]    When the Plunger piston  4  is actuated, the first valve piston  10  moves down due to combined force transfer of rubber spring stiffness. When First valve piston  10  moves down the Supporting element  23  forces the Second valve piston  30  to move down, as the Supporting element  23  is in contact with First valve piston  10 . Before the First valve piston  10  will open the First annular plate valve  14 , the Second valve piston  30  comes into contact with Second annular plate valve  37 , that means, the reaction force of the Compression spring  26  acts against the Compression spring  40 , what facilitates easy opening of the Second annular plate valve  37 . 
         [0034]    On further actuation of the Plunger piston  4 , the first valve piston  10  moves down and opens First annular plate valve  14 , resulting in a connection of the air supply to the delivery port. As the Supporting element  23  is already in contact with the First valve piston  10 , delivery air from top circuit just moves down to the Second valve piston  30  and opens Second annular plate valve  37  without any additional pressure build up in top circuit. 
         [0035]    This arrangement is conventionally termed as a Delta P reduction arrangement. It helps in delivering approximately the same delivery pressure in both top and bottom circuit without much time lag. 
         [0036]    All the features which are mentioned in the above description of the figures, in the claims and in the introduction of the description can be used both individually and in any desired combination with one another. The invention is therefore not restricted to the described and claimed combinations of features, but rather all combinations of features are to be considered to be disclosed. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Control valve 
           2  Housing upper part 
           2   a  Cylindrical guide in the housing upper part  2   
           3  Housing lower part 
           4  Plunger piston 
           4   a  First cylindrical projection of the plunger piston  4   
           4   b  Second cylindrical projection of the plunger piston  4   
           4   c  Cylindrical region of the plunger piston  4   
           5  Pressure plate 
           5   a  Hollow-cylindrical projection of the pressure plate  5   
           6  Groove 
           7  Securing ring 
           8  Folding bellows 
           9  Elastomer spring element 
           9   a  Sealing lip 
           9   b  Annular protrusion 
           9   c  Smaller diameter region of the elastomer spring element 
           9   d  Larger diameter region of the elastomer spring element 
           10  First valve piston 
           10   a  Undercut groove in the first valve piston 
           10   b  First cylindrical bore in the first valve piston 
           10   c  Second cylindrical bore in the first valve piston 
           11  Radial, head-shaped protrusion in the first valve piston 
           12  Hollow-cylindrical projection of the first valve piston  10   
           13  Annular sealing seat on the hollow-cylindrical projection  12  of the first valve piston 
           14  First annular plate valve 
           14   a  Hollow-cylindrical projection on the first annular plate valve  14   
           15  Radial sealing face on the first annular plate valve  14   
           16  First non-displaceable sealing seat in the housing upper part  2   
           17  First pressure space 
           17   a  Second pressure space 
           18  Venting passage 
           19  Securing ring 
           20  Back-pressure spring 
           21  Compression spring 
           22  Brake pressure space for a first brake circuit 
           23  Supporting element 
           24  Lip seal 
           25  Securing ring 
           26  Compression spring 
           27  Supporting disc 
           27   a  Perforation 
           28  Securing ring 
           29  Sealing ring 
           30  Second valve piston 
           31  Sealing ring 
           32  Sealing ring 
           33  Sealing ring 
           34  Annular sealing seat on the second valve piston  30   
           35  Second non-displaceable sealing seat in the housing lower part  3   
           36  Hollow-cylindrical projection on the housing lower part  3   
           37  Second annular plate valve 
           37   a  Hollow-cylindrical projection of the second annular plate valve  37   
           38  Radial sealing face on the second annular plate valve  37   
           39  Second brake pressure space for a second brake circuit 
           40  Compression spring 
           41  Lip seal 
           42  Supporting ring 
           42   a  Radial spokes 
           42   b  Cylindrical guide 
           43  Securing ring 
           44  Venting cap