Abstract:
A combined service brake and the stored-energy brake cylinder is provided, in which a ventilation valve which forms or shuts off a flow connection between the spring chamber and the service brake chamber of the brake cylinder ensures that disruptive noise is avoided while also preventing loss of air volume for building up the service brake force.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase of PCT International Application No. PCT/EP2006/011576, filed on Dec. 1, 2006, which claims priority under 35 U.S.C. §119 to German Application No. 20 2005 018 886.7, filed Dec. 2, 2005, the entire disclosures of which are expressly incorporated by reference herein. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention proceeds from a combined service brake and stored-energy brake cylinder having a diaphragm which is arranged in a housing of the service brake cylinder, can be loaded with pressure and delimits a service brake chamber which can be loaded with a service brake pressure on one side and a chamber which accommodates restoring springs on the other side, a stored-energy brake piston which is arranged in a housing of the stored-energy brake cylinder, can be actuated by a storage spring, delimits a stored-energy brake chamber on one side and a spring chamber which accommodates a storage spring on the other side, and has a piston rod which carries a venting valve which produces or shuts off a flow connection between the spring chamber and the service brake chamber, according to the preamble of claim  1 . 
     A combined service brake and stored-energy brake cylinder of this type is known, for example, from DE 40 11 739 A1. There, the venting valve is arranged on the end side in the hollow piston tube of the stored-energy brake piston which can project into the service brake chamber depending on the operating state. The venting valve has the object of dissipating the excess pressure which is produced in the spring chamber by the retraction of the service brake piston and the resultant reducing volume of said spring chamber when the parking brake is released, by said venting valve being switched into the open position by said excess pressure and producing a flow connection between the spring chamber and the service brake chamber. When driving off on a flat driving path, the service brake chamber is ventilated and is associated with ventilation of a pressure control module, since a service brake operation is not necessary after release of the parking brake. Then, at least a part of the excess air volume in the spring chamber can flow out, which as a consequence does not pass directly from there into the atmosphere, but rather via the aerating and venting path of the service brake chamber. In this context, internal ventilation is therefore also spoken of. 
     When driving off on an uphill driving path, it is necessary, however, when the parking brake is firstly applied to additionally apply the service brake at least briefly before the parking brake is released, in order to prevent the vehicle from rolling backward when driving off. In this case, the service brake chamber is ventilated. If the driver demands sufficiently high braking, the service brake pressure which prevails in the service brake chamber and at the same time on one side of the piston is capable of holding said piston on the valve seat counter to the action of the pressure is built up in the spring chamber and, as a result, of holding the venting valve closed. If, however, the service brake pressure and/or the service brake pressure gradient are/is below certain threshold values on account of a correspondingly low service brake demand of the driver, the service brake pressure which prevails on one side of the piston is not sufficient to hold the venting valve closed. Compressed air then flows from the service brake chamber via the open venting valve into the spring chamber. From there, it escapes via the piston seal and the housing seal into the atmosphere, which firstly causes disruptive noise; secondly, the air volume which flows out via the venting valve is no longer available for building up the service brake force. 
     The present invention is based on the object of developing a combined service brake and stored-energy brake cylinder of the type mentioned in the introduction in such a way that the abovementioned disadvantages are avoided. 
     According to the invention, this object is achieved by the features of claim  1 . 
     The venting valve of the combined service brake and stored-energy cylinder according to the invention has the following characterizing features:
     a) a piston is provided which carries a valve body and is guided axially displaceably in a cylinder which is formed on the piston rod,   b) at least one compression spring which is supported on the piston loads the valve body against a first valve seat on the piston and against a second valve seat on the cylinder,   c) the valve body is loaded by the pressure in the spring chamber in a direction which lifts it up from the first valve seat and from the second valve seat,   d) the piston is loaded by the pressure in the service brake chamber in a direction which presses the first valve seat against the valve body and lifts the valve body up from the second valve seat,   e) a flow connection being produced between the service brake chamber and the spring chamber when the valve body is lifted up from the first valve seat and/or from the second valve seat.   

     These measures ensure that the venting valve remains closed if, when the parking brake is applied, the service brake is applied at the same time. No more compressed air can therefore cross from the service brake chamber via the venting valve into the spring chamber and escape from there into the atmosphere, as a result of which disruptive noise is prevented. 
     Advantageous developments and improvements of the invention which is specified in the independent claims are possible as a result of the measures which are cited in the subclaims. 
     More precise details are apparent from the following description of exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, an exemplary embodiment of the invention is shown in the drawing and explained in greater detail in the following description. In the drawing: 
         FIG. 1  shows a sectional illustration of a combined service brake and stored-energy brake cylinder according to a preferred exemplary embodiment of the invention, with a venting valve; 
         FIG. 2  shows the venting valve from  FIG. 1  in the closed position; 
         FIG. 3  shows the venting valve from  FIG. 1  in an open position during the application of the parking brake; and 
         FIG. 4  shows the venting valve from  FIG. 1  in an open position during the release of the parking brake. 
     
    
    
     DETAILED DESCRIPTION 
     For the exemplary explanation of the invention,  FIG. 1  shows a combined service brake and stored-energy brake cylinder  1 , called a combined cylinder in the following case. The combined cylinder comprises a service brake cylinder  2  and a stored-energy brake cylinder  4  which is connected structurally and functionally to the former. The service brake cylinder  2  and the stored-energy brake cylinder  4  are divided from one another by an intermediate wall  6 . A stored-energy brake piston  8  is arranged displaceably within the stored-energy brake cylinder  4 , a storage spring  10  bearing against one side of the stored-energy brake piston  8 . On its opposite side, the storage spring  10  is supported on the base of the stored-energy brake cylinder  4 . 
     A stored-energy brake chamber  12  is formed between the stored-energy brake piston  8  and the intermediate wall  6 , which stored-energy brake chamber  12  is connected to a pressure control module which is not shown for scale reasons, in order to aerate and ventilate the latter. In the case of aeration, the stored-energy brake piston  8  is pushed axially into the release position of the parking brake under stress of the storage spring  10 . During this displacement of the stored-energy brake piston  8 , the air which is present within the spring chamber  14  which accommodates the storage spring  10  is pressed out via a venting valve  16 . If, in contrast, the stored-energy brake chamber  12  is ventilated for the purpose of braking, the storage spring  10  is capable of displacing the stored-energy brake piston  8  into the application position. 
     The stored-energy brake piston  8  is connected to a hollow piston rod  18  which extends through the intermediate wall  6  into a service brake chamber  20  of the service brake cylinder  2 . A seal  22  which is inserted in the intermediate wall  6  seals with respect to the outer wall of the piston rod  18  during its longitudinal movement. An inlet  23 , via which compressed air is let in and discharged in order to actuate the service brake cylinder  2 , opens into the service brake chamber  20 . The compressed air acts on a diaphragm  24  which is inserted within the service brake cylinder  2  and on the opposite side of which a pressure piece is provided in the form of a diaphragm plate  26 . The diaphragm plate  26  is connected to a push rod  28  which interacts with a brake actuating mechanism outside the combined cylinder  1 . This can be, for example, actuating elements of a disk brake of a motor vehicle. The service brake cylinder  2  is an active brake cylinder, that is to say the service brake is applied by aerating the service brake chamber  20  and is released by ventilation. A restoring spring (not shown) which is supported on one side on the diaphragm plate  26  and on the other side on the base of the service brake cylinder  2  ensures that the push rod  28  is restored into the release position in the case of a ventilated service brake chamber  20 . 
     The venting valve  16  is arranged in that end of the piston rod  18  which points away from the stored-energy brake piston  8 , and is accommodated in its interior space  32 , to be more precise. Although, furthermore, an emergency release device  34  of no further interest here is arranged there, the interior space  32  of the piston rod  18  can communicate with the spring chamber  14 . 
     According to  FIG. 2 , the venting valve  16  of the combined service brake and stored-energy cylinder has the following features:
     a) a piston  38  is provided which carries a valve body  36  and is guided axially displaceably in a cylinder  40  which is formed on the piston rod  18 ,   b) at least one compression spring  42  which is supported on the piston  38  loads the valve body  36  against a first valve seat  44  on the piston  38  and against a second valve seat  48  on the cylinder  40 ,   c) the valve body  36  is loaded by the pressure in the spring chamber  14  in a direction which lifts it up from the first valve seat  44  and from the second valve seat  48 ,   d) the piston  38  is loaded by the pressure in the service brake chamber  20  in a direction which presses the first valve seat  44  against the valve body  36  and lifts the valve body  36  up from the second valve seat  48 ,   e) a third valve seat  46  is formed between the piston  38  and a base  74  of the cylinder  40 ,   f) at least one position of the piston  38  existing, in which the first valve seat  44  is lifted up from the valve body  36 , the valve body  36  seals against the second valve seat  48 , the piston  38  is lifted up from the third valve seat  46  and is then loaded by the pressure in the service brake chamber  20  in a direction which lifts the first valve seat  44  up from the valve body  36 , and,   g) when the valve body  36  is lifted up from the first valve seat  44  and/or from the second valve seat  48 , a flow connection is produced between the service brake chamber  20  and the spring chamber  14 .   

     As is apparent from  FIG. 2  to  FIG. 4 , the piston  38  essentially has three sections; a first piston section which faces the spring chamber  14  and has a first piston plate  54 , on which a first piston face  50  and a second piston face  52  are formed; a second piston section which adjoins said first piston section and is configured as a piston rod  56 ; and a third piston section which is configured as a second piston plate  58  and on which a third piston face  60  and a fourth piston face  62  are formed. The cylinder  40  is held in a rotationally and axially fixed manner in the interior space  32  of the piston rod  18 . The piston  40  is guided axially in the cylinder  40  substantially by the second piston plate  58 , there being no tight guidance, however, but rather a narrow annular channel  59  being formed between the radially outer circumferential face of the second piston plate  58  and the radially inner circumferential face of the cylinder  40 , through which annular channel  59  compressed air can flow. 
     A first chamber  66  is formed between the third piston face  60 , the radially inner circumferential face of the cylinder  40  and a further base  64  of the cylinder  40 , the base  64  of the cylinder  40  having a central through opening, through which the first piston plate  54  can extend. On its face which points toward the first chamber  66 , the second valve seat  48  is formed on the base  64  of the cylinder  40 . The first valve seat  44  is situated on the second piston face  52  of the piston  38 , which second piston face  52  points toward the first chamber  66 . Furthermore, the compression spring  42  is accommodated in the first chamber  66 , which compression spring  42  is supported on one side on the valve body  36  and on the other side on the third piston face  60  on the second piston plate  58 . The compression spring  42  is installed in a prestressed state. 
     The valve body  36  is preferably configured as a ring which surrounds the piston rod  56  and the outer diameter of which is smaller than the inner diameter of the cylinder  40 , with the result that there is an inside annular gap between the ring  36  and the cylinder  40 . The ring  36  therefore seals against the first valve seat  44  on the first piston plate  54  or against the second valve seat  48  on the base  64  of the cylinder  40  only in the axial direction. 
     The first chamber  66  is constantly (that is to say, in every axial position of the piston  38 ) flow connected to an annular chamber  70  by means of at least one radial through hole  68  in the cylinder  40 . Said annular chamber  70  surrounds the cylinder  40  and is in turn connected to the service brake chamber  20  via at least one radial through hole  72  in the piston rod  18 . Furthermore, a third chamber  76  is formed between the second piston plate  58  and the base  74  of the cylinder  40 . 
       FIG. 2  shows the venting valve  16  in the closed position, that is to say the ring  36  bears in an axially sealing manner against the first valve seat  44  and against the second valve seat  48  and, as a consequence, there is no flow connection between the interior space  32  of the piston rod  18 , which interior space  32  is under the pressure of the spring chamber  14 , and the annular chamber  70  which is connected to the service brake chamber  20 . Furthermore, the piston  38  seals against the third valve seat  46  in this position, with the result that there is no flow connection between the third chamber  76  and the first chamber  66 . 
     Proceeding from this state, in which neither the service brake nor the parking brake is actuated, the parking brake is then applied while the service brake is still released. The spring chamber  14  is enlarged suddenly by the stored-energy brake piston  12  which is displaced by the storage spring  10 , as a result of which the pressure in said spring chamber  14  drops to a pronounced extent, for example below atmospheric pressure. The relatively low pressure of the spring chamber  14  therefore acts on the first piston face  50 ; the second piston face  52  and the third piston face  60  are loaded by the pressure of the service brake chamber  20 , which pressure corresponds approximately to atmospheric pressure. 
     As a result of the pressure difference, the piston  38  in  FIG. 3  is displaced to the right counter to the action of the shortening first compression spring  42 , as a result of which the first valve seat  44  lifts up from the ring  36  and a flow cross section is opened, as a result of which air can flow out of the service brake chamber  20  via the through hole  72  in the piston rod  18  into the annular chamber  70 , from there via the radial through hole  68  in the cylinder  40  into the first chamber  66  and finally from there into the interior space  32  of the piston rod  18 , which interior space  32  is in turn connected to the spring chamber  14  such that pressure is conducted. Pressure equalization can therefore take place between the spring chamber  14  and the service brake chamber  20 . In contrast, the ring  36  remains pressed sealingly against the second valve seat  48  on the base  64  of the cylinder  40  as a result of the action of the compression spring  42 . 
     As a result of the displacement of the piston  38  to the right in  FIG. 3 , it lifts up from the third valve seat  46 , as a result of which a flow connection is produced between the annular channel  59 , which is under the pressure of the service brake chamber, and the third chamber  76  which is gradually loaded as a consequence with this pressure which corresponds approximately to atmospheric pressure. This results in a further pressure force on the piston  38  which acts to the right in the figure, which piston  38  is loaded as a result in a direction which lifts the first valve seat  44  up from the valve body  36 . 
     The gradually increasing pressure in the spring chamber  14  also loads the third piston face  60 , with the result that the piston  38  is displaced to the left in  FIG. 3  as a consequence of the pressure force which results there, until the first valve seat  44  again comes into sealing contact with the ring  36 . At the same time, the piston  38  also comes into contact again with the valve seat  46  on the base  74  of the cylinder  40 . This movement is assisted by the spring force of the first compression spring  42  until the venting valve  16  is situated again in the position which is shown in  FIG. 2 . 
     When the parking brake is released, the pressure rises in the spring chamber  14  as a consequence of its reduction in size. As can be understood readily using  FIG. 4 , this increased pressure acts on the ring  36 , as a result of which the latter moves to the left counter to the action of the shortening compression spring  42 . The ring  36  therefore lifts up both from the first valve seat  44  and from the second valve seat  48 . Since the ring  36  seals radially neither against the cylinder  40  nor against the piston rod  56 , but rather an annular gap is always left free, compressed air can then flow from the spring chamber  14  via the interior space  32  of the piston rod  18 , the first chamber  66 , the through hole  68  in the cylinder  40 , the annular chamber  70  and the through hole  72  in the piston rod  18  into the service brake chamber  20  which is loaded with a lower pressure in comparison. After pressure equalization has been carried out between the spring chamber  14  and the service brake chamber  20 , the ring  36  is moved to the right into the closed position as a consequence of the action of the compression spring  42 , in which closed position said ring  36  bears axially sealingly again against the first valve seat  44  and against the second valve seat  48 . 
       FIG. 2  also identifies a closed position of the venting valve  16 , which position is set when the service brake is actuated additionally during application of the parking brake. A situation of this type results, for example, during driving off uphill. When the parking brake is applied, the pressure in the spring chamber  14  drops, as already explained with respect to  FIG. 3 , which leads to the piston  38  moving to the right. After pressure equalization has been carried out between the spring chamber  14  and the service brake chamber  20 , that is to say at a pressure in the spring chamber  14  which is increased by the inflow of air from the service brake chamber  20 , said increased pressure and the compression spring  42  reinstate the closed position. If, proceeding from this state, the service brake is then additionally actuated, the pressure rises in the service brake chamber  20 . This increased service brake pressure then also prevails in the first chamber  66  because compressed air can pass there via the through hole  72  in the piston rod  18 , the annular chamber  70  and the through hole  68  in the cylinder  40 . This service brake pressure also acts on the ring  36 , as a result of which the latter increases its sealing action against the first valve seat  44  and the second valve seat  48  and assists the action of the first compression spring  42  which holds the ring  36  there. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
     LIST OF DESIGNATIONS 
     
         
           1  Service brake and spring accumulator 
           2  Service brake cylinder 
           4  Stored-energy brake cylinder 
           6  Intermediate wall 
           8  Stored-energy brake piston 
           10  Storage spring 
           12  Stored-energy brake chamber 
           14  Spring chamber 
           16  Venting valve 
           18  Piston rod 
           20  Service brake chamber 
           22  Seal 
           23  Inlet 
           24  Diaphragm 
           26  Diaphragm plate 
           28  Push rod 
           32  Interior space 
           34  Emergency release device 
           36  Valve body 
           38  Piston 
           40  Cylinder 
           42  Compression spring 
           44  First valve seat 
           46  Third valve seat 
           48  Second valve seat 
           50  First piston face 
           52  Second piston face 
           54  First piston plate 
           56  Piston rod 
           58  Second piston plate 
           59  Annular channel 
           60  Third piston face 
           62  Fourth piston face 
           64  Base 
           66  First chamber 
           68  Through hole 
           70  Annular chamber 
           72  Through hole 
           74  Base 
           76  Third chamber