Abstract:
The invention relates to a device for producing and providing a vacuum for a vacuum consumer, having a vacuum source, having a suction valve, having a non-return valve arranged between the vacuum consumer and the suction valve, and having a ventilation valve, the control inlet of which ventilation valve is connected to the suction port of the vacuum source, the output of which ventilation valve opens out between the control valve and the non-return valve, and the input of which ventilation valve is open to the environment.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2009/058105, filed Jun. 29, 2009, which designated the United States and has been published as International Publication No. WO 2010/000694 and which claims the priority of German Patent Application, Serial No. 10 2008 032 242.3, filed Jul. 1, 2008, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for producing and providing a vacuum for a vacuum consumer. The invention also relates to a ventilation valve. 
     Devices of this type for producing and providing a vacuum are used, for example, in vehicles for operating a brake booster. One problem is that when the vehicle is stationary and the engine is switched off, the vacuum in the brake booster slowly decreases due to leakage, in particular in the vacuum generator and up to the suction valve, approaching atmospheric pressure. As a result, the brake pedal cannot be moved when attempting to start the vehicle and hence the trigger point required for starting cannot be attained in vehicles with automatic transmissions, so that the vehicle cannot be started. Responsible is here the check valve upstream of the brake booster which, unlike the suction valve, does not have a return spring. 
     It is therefore an object of the invention to provide an apparatus and/or a ventilation valve which reduces the risk that the brake booster is slowly vented. 
     SUMMARY OF THE INVENTION 
     This object is solved with an apparatus for producing and providing a vacuum for a vacuum consumer, with a vacuum source, a suction valve, a check valve arranged between the vacuum consumer and the suction valve, and a ventilation valve having a control input connected to the suction port of the vacuum source and an output terminating between the suction valve and check valve and an input which is open to atmosphere. 
     The apparatus of the invention has the significant advantage that with the ventilation valve the line segment between the suction valve and the check valve, which is located immediately before the vacuum consumer, i.e., the brake booster, is vented, so that the check valve assumes its closed position, if it has a neutral equilibrium position. The check valve does not have a return or closure spring, because a closure spring which always holds the check valve in a defined closed position, would significantly limit the pumping efficiency of the vacuum source, i.e., the vacuum pump. For this reason, the check valve, unlike the suction valve, does not have a closure spring or return spring. The check valve can always assume a neutral equilibrium position when the pressure is identical before and after the check valve. 
     However, if the region between the suction valve and the check valve is vented, then the check valve always assumes its closed position, because it is pressed into its closed position by the pressure difference before and after the closure member, thereby maintaining the vacuum in the brake booster. The vehicle can then be started without any problem even after a long stoppage or in the event of leakage in the supply lines; in particular, in vehicles with automatic transmission, the brake pedal always reaches the release point required for starting. 
     According to another embodiment of the invention, the ventilation valve has a housing with three pressure chambers wherein the control input terminates in the first pressure chamber; the second pressure chamber is according to the invention connected via an input or an opening to atmosphere, wherein the output of the ventilation valve exits from the third pressure chamber. According to the invention, the first pressure chamber includes a wall constructed in sections formed by an elastic membrane. This elastic membrane is deformed responsive to the pressure in the first pressure chamber and operates as a drive for a tappet. Depending on the pressure in the first pressure chamber, the tappet assumes a position corresponding to the pressure, starting from a threshold value. 
     According to another embodiment, the tappet has a valve element separating the second from the third pressure chamber. In other words, the second pressure chamber can be connected with the third pressure chamber with the tappet by moving the valve element with the tappet. Opening or closing this valve therefore depends on the pressure in the first pressure chamber. 
     To obtain an unambiguous valve position and to produce a defined opening pressure (threshold value), the valve element is a biased in the direction of the valve seat, in particular with a spring. The bias force can preferably be adjustable, with the bias force operating against the pressure in the first pressure chamber. 
     To reduce the manufacturing cost of the ventilation valve, the housing is constructed of two, in particular identical, barrel-shaped housing parts, which have openings facing each other and being flanged to each other. The housing can then be relatively easily provisioned and subsequently mounted. 
     The aforementioned object is also solved with a ventilation valve having the aforementioned properties and features. 
     Additional advantages, characteristic features and details of the invention are recited in the dependent claims and in the following description, where a particularly preferred exemplary embodiment is described in more detail with reference to the drawing. The features illustrated in the drawing and described in the description of the claims can be important for the invention either individually or in any combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The drawing shows in: 
         FIG. 1  the apparatus according to the invention with a closed ventilation valve in a longitudinal sectional view; and 
         FIG. 2  the apparatus according to  FIG. 1  with the ventilation valve in the open position. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an apparatus having the overall reference symbol  10  capable of producing and providing a vacuum for a vacuum consumer  12 , for example a brake booster  14  for a vehicle. A vacuum source  16 , for example a vacuum pump  18 , is provided which has a suction port  20  equipped with a suction valve  22 . The suction valve  22  is held in a defined closed position by a closure spring  24  or return spring. The suction valve  22  is connected via a line  26  with a check valve  28 , wherein the check valve  28  is constructed without a closure spring. The check valve  28  is then connected to the vacuum consumer  12 , i.e., the brake booster  14 . 
       FIG. 1  also shows a ventilation valve  30  which has a housing  34  constructed of two identical housing parts  32 . A first pressure chamber  36 , a second pressure chamber  38  and a third pressure chamber  40  are formed in the housing  34 . The first pressure chamber  36  has a control input  42  which is connected to the suction port  20  or the vacuum source  16  itself. The second pressure chamber  48  has two inputs configured as openings  44  which connect the pressure chamber  48  to atmosphere  46 , so that air can flow in the direction of the arrow  48 . The third pressure chamber  40  has an output which is connected to the line  26 . 
     The two housing parts  32  have a shoulder  52  disposed at a transition from the second pressure chamber  38  to the first pressure chamber  36  as well as from the second pressure chamber  38  to the third pressure chamber  40 , allowing an inner housing  54  to be clamped between the two shoulders  52 . This inner housing  54  has two plates  56  at the respective ends, with each plate sealingly received by the two housing parts  32  with a seal  58 , for example an O-ring, and with the two plates  56  being connected with each other by way of a sleeve  60 . 
     The inner housing  54  is formed as a single piece and has a central bore  62  in which a tappet  68  is supported for movement in the direction of the longitudinal axis of the ventilation valve  30 . The upper end of the tappet  64  contacts a membrane  66  which forms one wall of the first pressure chamber  36  and which is clamped at its edge between the shoulder  52  and one of the plates  56  of the inner housing  54 . The lower part of the tappet  64  is equipped with a valve element  68 , it in particular a sealing disk  70 , which is oriented parallel on the lower plate  56  of the inner housing  54 , with the tappet  64  being biased in the direction of the plate  56  by way of a coil spring  72 . The valve element  68  seals through openings  74  which extend through the lower plate  56  and connect the second pressure chamber  38  with the third pressure chamber  40 . 
       FIG. 1  shows the closed position of the valve element  68 , wherein the valve element  68  contacts a plate  56  forming a valve seat  76 . In  FIG. 2 , the valve element  68  is lifted from the valve seat  76 . 
     The functionality of the apparatus  10  will now be described. The vacuum source  18  produces a vacuum which is supplied via connecting lines not only to the vacuum consumer  12 , but also to the first pressure chamber  36  and the third pressure chamber  40 . When the vacuum source  16  is switched off, for example when the motor of a vehicle is stopped, then the suction valve  22  is closed by the closure spring  24 , whereas the check valve  28  can assume a neutral equilibrium position, because the closure member is not urged into the closed position by a closure spring and the pressure difference before and after the check valve  28  is too small to produce an air flow capable of urging the valve member of the check valve  28  into the closed position. 
     Leaks in the vacuum source or also in the line to the check valve  28  may reduce the original vacuum therein of about 80 mbar (absolute) slowly towards the ambient pressure (1024 mbar). Because the suction port  20  is connected with a control input  42  of the ventilation valve  30 , the vacuum in the first pressure chamber  36  decreases accordingly. This increase in the absolute pressure operates on the membrane  66 , thereby exerting a force F M  on the tappet  64  in the direction of the valve element  68 . However, the closure force F F  of a spring  72  minus the force F D  of the atmospheric pressure, which operates on the valve element  68  via the through openings  74 , operates against this force F M . If the sum of the forces F M  and F D  is greater than the closure force F F , then the valve element  68  is lifted from the valve seat  76  which, as mentioned above, is illustrated in  FIG. 2 . The through openings  74  are now open and the third pressure chamber  40  is (briefly) connected with the second pressure chamber  38  and hence via the openings  44  to atmosphere  46 , allowing air to flow into the third pressure chamber  40  in the direction of the arrows  48 . The line  26  is vented via the output  50 , with the temporary airflow cause by the pressure difference before and after the check valve  28  urging the check valve  28  into its defined closed position, so that the vacuum in the vacuum consumer  12  can be maintained. The check valve  28  assumes its closed position in any case, because the pressure difference before and after the check valve  28  is large enough to urge its closure member securely against its valve seat. The air flowing into the line  26  is oil-free and can also be delivered through a filter, making it also dust-free. 
     With the apparatus  10  according to the invention and particularly with the ventilation valve  30  according to the invention, a vacuum is always reliably supplied to the vacuum consumer  12 , in particular the brake booster  14 , even if the vacuum source  16  is not operating.