Abstract:
The invention relates to a motor vehicle vacuum pump having a pump housing surface, on which a noise absorption cap is mounted, said cap defining a noise damping volume.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage of International Application No. PCT/EP2015/053577, filed Feb. 20, 2015 and which claims priority to German Application No. 10 2014 207 023.6 filed Apr. 11, 2014. The entire disclosure of each of the above listed applications is incorporated herein by reference. 
       FIELD 
       [0002]    The invention relates to a motor vehicle vacuum pump having a pump housing surface, on which a noise absorption cap is mounted, said cap defining a noise damping volume. 
       BACKGROUND 
       [0003]    As part of ever stricter regulations relating to environmental protection, motor vehicle manufacturers are being compelled to design engines to be efficient and to have a low consumption. An automatic start-stop system is already available in almost all vehicles. Moreover, there is increasingly the possibility of switching off the internal combustion engine while coasting. 
         [0004]    With such switching concepts for the internal combustion engine, it is hardly possible to use a mechanical vacuum pump for servo assistance of the braking force. There is therefore a demand for electric vacuum pumps for modern applications. These vacuum pumps often run dry since it is also no longer possible to supply the vacuum pump with oil in a manner dependent on a running internal combustion engine. 
         [0005]    The absence of the engine noise of the internal combustion engine brings the operating noise of the vacuum pumps to the fore in terms of what is audible. In order to minimize these operating noises, various measures are implemented in order to reduce structure borne noise and airborne noise. 
         [0006]    The publication WO 2011/134448 A2 discloses a vacuum pump having a pump housing, in which pump at least one pump housing part is formed by a sandwich-type sheet metal material comprising two sheet metal layers, between which is arranged a plastic layer, by means of which the sheet metal layers are vibrationally decoupled from one another. The vacuum pump can comprise a muffler, which is formed from the sandwich-type sheet metal material. Vacuum pumps having noise absorption caps are known from PCT/DE2013/100370 (not a prior publication). In addition, a multifunctional decoupling element is arranged between the pump housing surface and the noise absorption cap, said cap performing a sealing function and, in this prior art, also a valve function in addition to a noise decoupling function. 
         [0007]    The decoupling element serves to decouple the noise absorption cap acoustically, particularly in respect of vibrations and/or structure borne noise occurring during the operation of the motor vehicle vacuum pump. By virtue of the acoustic decoupling of the noise absorption cap brought about by means of the decoupling element, unwanted development of noise during the operation of the motor vehicle vacuum pump can be considerably reduced. The decoupling element also forms a seal between the pump housing surface and the noise absorption cap with respect to the environment of the motor vehicle vacuum pump. A separate seal between the pump housing surface and the noise absorption cap can thus be omitted. 
         [0008]    However, it is not possible, using the measures of damping the airborne noise by means of the noise absorption cap and damping the structure borne noise by means of the decoupling element, for all the structure borne noise to be suppressed and, specifically, for the noise peaks at the resonant frequencies to be reduced. 
         [0009]    It is an object of the invention to further optimize a motor vehicle vacuum pump having a pump housing surface, on which a noise absorption cap defining a noise damping volume is mounted, in respect of unwanted development of noise during the operation of the motor vehicle vacuum pump. 
       SUMMARY 
       [0010]    The object is achieved by means of a motor vehicle vacuum pump having a pump housing surface, on which a noise absorption cap is mounted, said cap defining a noise damping volume, wherein a double-sided adhesive connector is arranged between the pump housing surface and the noise absorption cap, said adhesive connector performing both a sealing function and a connecting function between the pump housing surface and the noise absorption cap in addition to a noise decoupling function. 
         [0011]    For simplicity of assembly, it is advantageous here that the double-sided adhesive connector ( 60 ) is formed integrally from a viscoelastic material. 
         [0012]    The use of a double-sided adhesive connector ( 60 ) made from an acrylate has proven particularly advantageous here. 
         [0013]    It is advantageous here that the double-sided adhesive connector is of annular design. In this case, it is not at all essential that the annular adhesive connector should follow the contour of the components to be connected, allowing the use of adhesive connectors of standard dimensions. 
         [0014]    The double-sided adhesive connector is advantageously of almost circular design. 
         [0015]    To increase the fastening area, it is advantageous that the noise absorption cap for the double-sided adhesive connector has surfaces for adhesive bonding and/or fastening lugs on the pump cover and on the noise absorption cap. 
         [0016]    It is advantageous that the double-sided adhesive connector is embodied and arranged in such a way that the noise absorption cap is acoustically decoupled from the pump housing surface and, in this way, the structure borne noise can be minimized. 
         [0017]    The embodiment in which the double-sided adhesive connector, the noise absorption cap and the pump housing surface differ in hardness in such a way that the noise absorption cap is substantially vibrationally decoupled from the pump housing surface and thus also compensates tolerances as regards deviations from the flatness of the surfaces to be joined is particularly advantageous. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0018]    Further advantages, features and details of the invention will become apparent from the following description, in which various illustrative embodiments are described in detail with reference to the drawing, in which: 
           [0019]      FIG. 1  shows an exploded view of a noise absorption cap of a motor vehicle vacuum pump in the prior art; 
           [0020]      FIG. 2  shows an illustration of a pump housing according to the invention with the noise absorption cap; and 
           [0021]      FIG. 3  shows an illustration of a pump cover surface upon which the noise absorption cap is installed. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1 and 2  show part of a motor vehicle vacuum pump  1  according to the invention having a pump housing  3 . The pump housing  3  comprises a housing pot (not shown), which is screwed to a pump cover  5 . It is possible to integrate into the housing pot a suction connection, via which a working medium, e.g. a gaseous medium, such as air or carbon dioxide, is drawn into a working chamber in the interior of the pump housing  3  when the motor vehicle vacuum pump  1  is driven. 
         [0023]    The motor vehicle vacuum pump  1  is embodied as a vane pump having one or more vanes and a rotor. The rotor is connected in terms of drive to an electric motor. The general construction and operation of a vane pump are described in the publication WO2011/134448 A2, for example. 
         [0024]    The motor vehicle vacuum pump  1  driven by the electric motor is operated without lubricating oil. The motor vehicle vacuum pump  1  operated without lubricating oil and driven by electric motor is installed in a motor vehicle, which can comprise a further drive in addition to an internal combustion engine drive, e.g. an electric motor drive. 
         [0025]    When the internal combustion engine drive is switched off, the motor vehicle vacuum pump  1  driven by the electric motor is operated in the motor vehicle in order to produce a reduced pressure, e.g. in a brake booster embodied as a vacuum-type booster. 
         [0026]    With its side facing away from a pump housing surface  8 , the pump cover  5  defines the working chamber of the motor vehicle vacuum pump  1 . Provided in the pump housing surface  8  is a passage opening  10 , which allows a gaseous working medium to pass through from the working chamber of the motor vehicle vacuum pump  1 . The passage opening  10  is embodied as a slotted hole and has the form of a circular arc in plan view. 
         [0027]    The pump cover  5  with the pump housing surface  8  has essentially the form of a circular disk, on which three fastening recesses  11 ,  12 ,  13  are formed radially on the outside. The fastening recesses  11  to  13  delimit through holes, through which fastening means can be passed. 
         [0028]    The pump cover  5  is formed from an aluminum material. The aluminum material is preferably a spray-compacted aluminum material. The spray-compacted aluminum material preferably has a silicon component of more than fifteen percent and contains particles of hard material. The aluminum material is preferably in the form of an alloy which, in addition to silicon, can also contain other elements, such as iron or nickel. The particles of hard material are preferably formed by silicon carbide. 
         [0029]    A decoupling element  20  and a noise absorption cap  30  are attached to the pump housing surface  8  of the pump cover  5 . The decoupling element  20  has substantially the same shape as the pump cover  5  but is formed from a different material than the pump cover  5 . Radially on the outside, three fastening lugs  21 ,  22 ,  23  are formed on the decoupling element  20 , said lugs, together with the fastening recesses  11  to  13  on the pump cover  5 , being used to fasten the noise absorption cap  30  of the decoupling element  20  and of the pump cover  5  on the pump housing pot (not shown). Flexible bushes are placed on the fastening lugs or, alternatively, are formed integrally, and surround the fastening means, namely the screws. 
         [0030]    The decoupling element  20  separates the noise absorption cap  30  vibrationally from the pump cover  5 . For this purpose, the decoupling element  20  is formed in this example from a silicone rubber material which is relatively soft in comparison with the aluminum material from which the pump cover  5  is formed. 
         [0031]    In addition to the noise decoupling function, the decoupling element  20  also performs a sealing function. The decoupling element  20  comprises a main body  25 , which has essentially the form of a circular disk. Two annular beads are formed radially on the outside on both sides of the main body  25 . 
         [0032]    The decoupling element  20  furthermore performs a valve function. For this purpose, a valve  28  is integrated into the decoupling element  20 . The valve  28  is embodied as a duckbill valve and is connected integrally to the main body  25  of the decoupling element  20 . The duckbill of the valve  28  extends from the pump housing surface  8  into the interior of the noise absorption cap  30 . 
         [0033]    Radially on the outside, the noise absorption cap  30  has a fastening flange with three fastening lugs  31 ,  32 ,  33 . The fastening lugs  31  to  33  are used for the passage of screws  35 ,  36 ,  37 , with the aid of which the noise absorption cap  30 , together with the decoupling element  20  and the pump cover  5 , can be fastened on the pump housing pot (not shown) of the pump housing  3 . 
         [0034]    The noise absorption cap  30  is formed from a plastic material of a hardness different from the materials from which the pump cover  5  and the decoupling element  20  are formed. 
         [0035]    Although the decoupling element  20  has bushes to receive the screws  35 ,  36 ,  37 , the screws transmit structure borne noise between the pump cover  5  and the noise absorption cap  30 . 
         [0036]      FIG. 2  shows the solution according to the invention, which shows a connection between the two components, the pump cover  5  and the noise absorption cap  30 , with the aid of a viscoelastic adhesive connector  60 . In one illustrative embodiment, an acrylate material that offers double-sided adhesive bonding, of the kind that can be obtained under the brand name 3M-4959 F, is used. The acrylate adhesive core of the material forms a virtually inseparable unit with the two functional adhesive surfaces. Unlike conventional foam adhesive strips, the adhesive, which is viscoelastic throughout, forms a durable, stress-free composite structure. Moreover, the adhesive connectors are vibration-damping and, by virtue of their closed-cell structure, have a sealing effect. 
         [0037]    By using the viscoelastic adhesive connector  60 , noise transmission by the screwed joint between the pump and the noise absorption cap is prevented. The structure borne noise, which propagates at about 250 Hz with the respective harmonic components based on the rotational frequency of the pump, is suppressed by the adhesive connector in an effective manner that is very specific to frequencies below 1000 Hz. 
         [0038]    Here, the frequencies caused by the vane rotations of the vacuum pump are damped very specifically by 10 dB, while the overall spectrum of the structure borne noise is damped by 5 dB. The fact that it is precisely frequencies in the lower range which are successfully reduced results in a significant improvement in terms of the subjective noise level. 
         [0039]    An optimum sealing function is achieved by adhesive bonding with the metallic or plastic substrate without the sealing element, the adhesive connector, needing to have additional grooves or structures. The metallic surface of the pump cover  5  is joined flat to the plastic surface of the noise absorption cap. 
         [0040]    The adhesive connector is a disk shaped ring which follows the outer contour of the pump cover and of the noise absorption cap. In  FIG. 2 , the adhesive connector is flush with the outer contour of the noise absorption cap and the circumferential rim  42  thereof. However, the adhesive connector can quite possibly be inserted and installed in such a way as to be set back. Because it is not absolutely necessary to follow the outer contour, only a sufficiently large joining surface being required, standard adhesive connectors with predetermined outside radii can be used. 
         [0041]      FIG. 3  shows a pump cover surface  8  on which an adhesive connector is arranged, on the right with a border a and on the left with a flush edge. It can be seen that there is a higher degree of freedom in the design of the outer contour of the pump if the adhesive connector does not also have to be adapted to the contour. 
         [0042]    In order to simplify assembly, a shallow groove, e.g. in the noise absorption cap in the surface of the circumferential rim, can be provided, allowing the adhesive connector to be positioned in a simple manner. For fastening, sealing and noise decoupling, it is not necessary for the pump cover  5  and the noise absorption cap  30  to have fastening lugs  21 ,  31  etc. The pump cover and the noise absorption cap can be produced without these protrusions and thus occupy a reduced installation space. 
         [0043]    In an alternative embodiment, use is made of fastening lugs and the shape of the adhesive connector is adapted in order to achieve a larger fastening surface. 
         [0044]    An advantageous embodiment uses a circular ring about 3 mm thick composed of the abovementioned material. 
         [0045]    It is entirely reasonable that person skilled in the art should interpret the term vacuum pump in a very wide sense, describing not only the production of a conventional vacuum but also the production of a reduced pressure that approaches a vacuum. The principle of the invention shown is not restricted to a reduced pressure to be achieved. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  motor vehicle vacuum pump 
           3  pump housing 
           5  pump cover 
           8  pump housing surface 
           10  passage opening 
           11  fastening recess 
           12  fastening recess 
           13  fastening recess 
           20  decoupling element 
           21  fastening lug 
           22  fastening lug 
           23  fastening lug 
           25  main body 
           28  valve 
           30  noise absorption cap 
           31  fastening lug 
           32  fastening lug 
           33  fastening lug 
           35  screw 
           36  screw 
           37  screw 
           42  circumferential rim 
           60  adhesive connector 
         a spacing