Abstract:
A motor vehicle vacuum pump includes a pumping chamber in which a pump rotor rotates to compress a gas, an outlet chamber into which the gas exits, a separation wall which includes a valve opening and a valve seat arranged on an outlet side of the separation wall around the valve opening. The separation wall separates the pumping chamber from the outlet chamber. An outlet valve is formed as a non-return valve in the separation wall. The outlet valve is formed by the valve opening in the separation wall and includes a valve body with a closing body. The outlet valve has the gas exit therethrough from the pumping chamber into the outlet chamber. A corresponding part of the closing body is supported on the valve seat when the closing body is in a closed position. The valve seat and/or the corresponding part of the closing body includes microgrooves.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
       [0001]    This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2015/052090, filed on Feb. 2, 2015 and which claims benefit to European Patent Application No. 14155617.5, filed on Feb. 18, 2014. The International Application was published in German on Aug. 27, 2015 as WO 2015/124415 A1 under PCT Article 21(2). 
       FIELD 
       [0002]    The present invention relates to a motor vehicle vacuum pump designed as a displacement pump, for example, as a vane pump. The motor vehicle vacuum pump is an auxiliary aggregate in a motor vehicle which is driven, for example, directly by an internal combustion engine or by a separate electric drive motor. 
       BACKGROUND 
       [0003]    The motor vehicle vacuum pump comprises a pumping chamber in which the pump rotor rotates, which rotor compresses a gas, generally air, in the pumping chamber and expels the gas into an outlet chamber via an outlet valve. The outlet valve prevents a return flow of compressed gas from the outlet chamber into the pumping chamber. A leaf spring valve is often used as the outlet valve due to its simple structure and high reliability, wherein the valve body is designed as a leaf spring which, in the closed position, rests on a valve seat surrounding the valve opening and is lifted off from the valve seat if the pressure difference is sufficient so that the outlet valve is opened. The generation of noise is problematic or at least undesirable with vacuum pumps having outlet valves, which noise results substantially from the fast acceleration of the valve body, the lubricant in case of a lubricated vacuum pump, and the sudden compression or decompression of the gas. 
         [0004]    A mechanical motor vehicle vacuum pump is described in DE 102 27 772 A1 wherein, for the purpose of noise reduction, a channel or an opening is provided near the outlet valve in order to gradually reduce pressure variations in this area. 
         [0005]    A mechanical motor vehicle vacuum pump is described in EP 1 953 389 A2 wherein, for the purpose of noise reduction, the valve body designed as a leaf spring is formed with an opening in order to gradually reduce pressure variations in this area. This design may cause a significant reduction of noise, however, the opening behavior and the generation of noise when the outlet valve opens are not always satisfactory, especially at high rotational speeds of the vacuum pump. 
       SUMMARY 
       [0006]    An aspect of the present invention is to provide a motor vehicle vacuum pump with reduced noise generation. 
         [0007]    In an embodiment, the present invention provides a motor vehicle vacuum pump which includes a pump rotor, a pumping chamber in which the pump rotor is arranged to rotate so as to provide a compressed gas, an outlet chamber into which the compressed gas exits from the pumping chamber, a separation wall comprising a valve opening and a valve seat arranged on an outlet side of the separation wall around the valve opening. The separation wall is configured to separate the pumping chamber from the outlet chamber. An outlet valve is formed as a non-return valve in the separation wall. The outlet valve is formed by the valve opening in the separation wall and comprises a valve body which comprises a closing body. The outlet valve is configured to have the compressed gas exit from the pumping chamber into the outlet chamber therethrough. A corresponding part of the closing body is supported on the valve seat when the closing body is in a closed position. At least one of the valve seat and the corresponding part of the closing body comprises microgrooves oriented in a lateral direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
           [0009]      FIG. 1  shows an open motor vehicle vacuum pump showing a separation wall which separates the pumping chamber from the outlet chamber in which an outlet valve is provided; 
           [0010]      FIG. 2  shows a top plan view of the separating wall including the valve seat in the area of the outlet valve; 
           [0011]      FIG. 3  shows a top plan view of the side of the valve body on the pumping chamber side in an embodiment; 
           [0012]      FIG. 4  shows a top plan view of the side of the valve body on the pumping chamber side in an embodiment; and 
           [0013]      FIG. 5  shows a cross section of the separating wall in the area of the outlet valve. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In an embodiment of the present invention, the valve seat and/or the corresponding part of the valve body closure body have a plurality of microgrooves directed in a quasi star-shaped manner in a lateral direction, that is, for example, in case of a circular valve opening, they are arranged almost radially. The microgrooves thereby form a drain in the closing plane of the outlet valve via so that a faster pressure compensation is effected in the interface between the valve seat and the corresponding part of the closure body when the outlet valve is opened. In case of an oil-lubricated vacuum pump, it is thereby in particular possible to significantly reduce the separation force necessary to overcome the adhesive force between the valve seat and the corresponding edge portion of the closure body. The opening movement of the closure body thereby becomes more harmonious so that noise generation during opening is also reduced. The closing movement also becomes more harmonious thereby so that noise generation during the closing of the outlet valve is also reduced. 
         [0015]    In an embodiment of the present invention, the groove depth t of the microgrooves can, for example, be less than 0.2 mm, for example, less than 0.1 mm. The groove width of the microgrooves can, for example, beless than 0.5 mm, for example, less than 0.25 mm. Tests have shown that relatively few microgrooves, for example, fewer than a total of 100 microgrooves, already cause a significant reduction of noise emissions. Because the microgrooves have a relatively small opening cross section, be it individually or in total, return flow losses caused by the microgrooves are negligible. 
         [0016]    In an embodiment of the present invention, the ratio of the length 1 of the microgrooves to their mutual lateral distance d can, for example, be greater than 1.0 for at least one half of the valve seat. In other words, the distance between two microgrooves is generally shorter than the length of the microgrooves. In an embodiment of the present invention, the microgrooves do not cross each other, but can, for example, be arranged in a star-shaped manner. In rectilinear regions of the valve seat, the microgrooves can, for example, be arranged in parallel with each other. 
         [0017]    In an embodiment of the present invention, the microgrooves can, for example, be provided either only on the valve seat or on the closure body. The microgrooves can, for example, only be provided on the valve seat that surrounds the valve opening. Positive noise emission effects are not significantly enhanced by providing the microgrooves both on the valve seat and on the closure body of the valve body so that the provision of the microgrooves on only one side of the interface allows manufacturing costs to be kept relatively low without suffering any functional disadvantage. 
         [0018]    In the closed state of the outlet valve, a longitudinal end of the microgrooves can, for example, be open to the valve opening and the other longitudinal end of the microgrooves can, for example, be open to the outlet chamber. When the outlet valve is fully closed, i.e., when the closure body fully rests on the valve seat, the two longitudinal ends of the microgrooves are open so that the maximum possible drainage function is available in the longitudinal direction of the grooves even when the outlet valve is completely closed. 
         [0019]    In an embodiment of the present invention, the valve seat can, for example, be formed with a raised shape. This simple measure in particular provides that the microgrooves are always open to the outlet chamber at their respective outer longitudinal end. 
         [0020]    In an embodiment of the present invention, the microgrooves can, for example, be manufactured via a laser engraving or a stamping. The opening and closing behavior of the outlet valve can thus be significantly improved using a relatively simple method. 
         [0021]    In an embodiment of the present invention, the valve body can, for example, be designed as a leaf spring. Such a conception of the valve body is economic and mechanically reliable. 
         [0022]    Two embodiments of the present invention will be explained in detail below with reference to the drawings. 
         [0023]      FIG. 1  shows an open motor vehicle vacuum pump  10 , wherein a separating wall  22  can be seen that separates a pumping chamber  12  from an outlet chamber  14 , as illustrated in the sectional view shown in  FIG. 5 . The vacuum pump  10  is a so-called mechanical vacuum pump mechanically driven by an internal combustion engine, i.e., rotating at a rotational speed proportional to the rotational speed of the internal combustion engine. For example, the vacuum pump  10  in the mounted state is driven directly via the camshaft of the internal combustion engine. 
         [0024]    The vacuum pump  10  is designed as a compressor pump and discontinuously compresses gas, in particular air. To prevent a return flow of the gas from the outlet chamber  14  back into the pumping chamber  12  between two pressure intervals, a separating wall  22  is provided with an outlet valve  20  that opens at a corresponding overpressure in the pumping chamber  12  and prevents a return flow of the gas from the outlet chamber  14  back into the pumping chamber  12  when no overpressure prevails. 
         [0025]    The outlet valve  20  is illustrated in section together with the separating wall  22  in  FIG. 5 . The outlet valve  20  is designed as a so-called leaf spring valve. An oblong curved valve opening  24  is provided in the separating wall  22 . On the outlet-chamber side  23  of the separating wall  22 , which is opposed by the pumping-chamber side  21 , a valve body  40 ;  40 ′ is fixed which is illustrated in a top view on its pumping-chamber side in a first embodiment in  FIG. 3  and in a second embodiment in  FIG. 4 . The valve body  40 ;  40 ′ has three sections in the longitudinal direction, namely, a closure body section  43 ;  43 ′, a hinge section  44 , and a fastening section  46 . 
         [0026]    The valve body  40 ;  40 ′ is made of spring sheet and has a constriction  45  in its hinge section  44 , whereby the valve body  40 ;  40 ′ is designed to be more easily flexed in the hinge section  44  than in the adjoining closure body section  43  and the fastening section  46 . In the fastening section  46 , the valve body  40 ;  40 ′ has a fastening opening  48  and a recess  52 . The valve body  40  is fixed by a fastener  50  in a bore  28  of the separating wall  22 , which bore  28  may be provided with a thread. The fastener  50  may be a screw, a rivet, or any another suitable fastener. The recess  52  embraces a raised holding nose  54  of the separating wall  22  so that the fastener  50  and the raised holding nose  54  fix the valve body  40  on the separating wall  22  in a defined and non-rotatable manner. The separating wall  22  has a hinge recess  26  in the area of the hinge section  44  of the valve body  40 . 
         [0027]    A closure body  42 ;  42 ′ is arranged at the other longitudinal end of the valve body  40 ;  40 ′, which closure body  42 ;  42 ′ completely closes the valve opening  24  in its closing position as illustrated in  FIG. 5 . 
         [0028]    The separating wall  22  has a valve seat  30  on the outlet side  23  which is designed to be raised with respect to the base plane of the separating wall  22  and to be plane, on which valve seat  30  the corresponding strip-shaped edge portion of the pumping-chamber side of the closure body, illustrated in  FIGS. 3 and 4 , rests in the closing position. The web-like valve seat  30  has a raised height of about 1 mm relative to the adjacent regions. 
         [0029]    In the first embodiment illustrated in  FIGS. 3 and 5 , the valve seat has 30 to 50 microgrooves  32  oriented in the lateral direction, i.e., the microgrooves  32  extend in a star-shaped manner from the inside outward and do not cross each other. The microgrooves  32  are oriented almost perpendicular with respect to the opening edge. The microgrooves  32  are formed in the valve seat  30  by laser engraving. The microgrooves  32  typically have a groove depth t of 0.025 mm and a groove width b of 0.1 mm. The length 1 of the microgrooves  32  may 1.0 to 2.0 mm, the lateral distance d between two adjacent microgrooves is less than 1.0 mm. The mean lateral distance d is always smaller than the length 1 of the microgrooves  32 . 
         [0030]    In a second embodiment, the valve body  40 ′ has microgrooves  32 ′ on its side facing to the valve seat  30 , which microgrooves  32 ′ have the same dimensions and orientation as the microgrooves  32  in the valve seat  30 . The valve body  40 ′ with the microgrooves  32 ′ may be combined with a valve seat without microgrooves or with a valve seat  30  as illustrated in  FIGS. 2 and 5  with microgrooves  32 . 
         [0031]    The microgrooves  32  on the valve seat  30  are open at their two longitudinal ends so that the outer longitudinal ends are open to the outlet chamber  14  and the inner longitudinal ends are open to the pumping chamber  12 . A fluid flow may thereby always flow into and out of the respective microgrooves at both longitudinal sides so that a corresponding pressure compensation is always possible in the microgroove  32 . A draining of the valve seat  30  is provided in all operating states of the outlet valve  20 . 
         [0032]    The vacuum pump  10  can, for example, be oil-lubricated so that oil in particular flows in and out through the microgrooves  32 ;  32 ′ during an opening and a closing operation. The valve body  40 ;  40 ′ is pre-tensioned so that it opens at a differential pressure of about  0 . 04  bar. Oil may flow through the microgrooves  32 ;  32 ′ towards the center of the opening already at the above-mentioned differential pressure so that the oil film between the valve seat  30  and the closure body  42 ;  42 ′ tears quickly. This allows for a harmonious opening movement of the valve body  40  so that the sound emissions are significantly reduced. This also analogously applies to the closing movement. 
         [0033]    The present invention is not limited to embodiments described herein; reference should be had to the appended claims.