Patent Publication Number: US-10774835-B2

Title: Vacuum pump with sound absorption and check valve

Description:
CROSS REFERENCE 
     This application claims priority to PCT Application No. PCT/EP2016/077550, filed Nov. 14, 2016, which itself claims priority to German Patent Application 10 2015 120304.9, filed Nov. 24, 2015, the entirety of both of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The preset invention pertains to a vacuum pump with a primarily cylinder-shaped pump housing, in which a rotor with slider elements is mounted to swivel, and having at least one air outlet opening, where a bowl-shaped sound-absorbing cover is attached on the pump housing and where a circumferential gap space for sound absorption is formed between the pump housing and the sound-absorbing cover and where the pump housing has an end face in which at least one air outlet opening is arranged and where an elastic upstream sound absorber element is arranged between the end face and the sound-absorbing cover so that an upstream chamber is formed between the upstream sound absorber element and the end face into which the air flows from the air outlet opening. 
     BACKGROUND 
     DE 10 2012 112 069 A1 discloses a category-defining vacuum pump, and an upstream sound-absorbing element made of a rubber-elastic material is installed between a bowl-shaped sound-absorbing cover and a pump housing. The air that escapes from the air outlet opening in the front side of the pump housing flows through a filter housed in the upstream sound-absorber element. The further course of the air flow goes between the sound-absorbing cover and the upstream sound absorber element until the air finally enters a circumferential gap space between the outside of the primarily cylinder-shaped pump housing and the sound-absorbing cover. 
     Vacuum pumps of this type are, in themselves, known and are also called vane pumps, and the vacuum pump also has a motor attached to the pump housing that initiates the rotation of the rotor with the slider elements. The sound absorber is necessary to prevent potential sound emissions when operating the vacuum pump. Vacuum pumps of the type of interest here are used to generate low pressure for the purpose of engine management or for brake force boost in a vehicle. In doing so, it is desirable for the vacuum pump to operate with as little noise as possible. 
     It is also known that in vacuum pumps of this type, when at a standstill, the conveyed air is sucked back from the upstream chamber into the pump housing through the air outlet opening. In the process, dirt, dust, suspended particles and the like can get into the pump housing, potentially resulting in premature failure of the vacuum pump. Therefore, a filter is used in the upstream sound absorber element, and the filter prevents dirt from entering the air outlet opening when the vacuum pump is idle. A disadvantage is that the filter forms a flow resistance, and moreover, there is an effect that separated substances in the filter can be flushed out of the filter, then return to the air outlet opening and thus to the pump housing. 
     SUMMARY OF THE INVENTION 
     The task of the invention is forming a vacuum pump with an advantageous sound absorber, which is also intended to prevent dirt from entering the air outlet opening when the pump is idle. The intention is to avoid the need to use a filter. 
     The invention includes the technical contribution that the upstream sound absorber element has a molded projection facing the end face with an air channel passing through the projection, where the projection is arranged at a distance from the end face during operation of the vacuum pump and, while the vacuum pump is idle, the projection makes contact with the end face through elastic deformation of the upstream sound absorber element, causing the air channel to be closed off and creating a check valve function. 
     The inventive solution attains a method whereby without the use of a filter, dirt is prevented from entering the air outlet opening and thus the pump housing. As soon as the vacuum pump is shut off, there is an immediate low pressure in the upstream chamber, which causes an elastic deformation of the upstream sound absorber element such that the projection reaches the end face on the top of the pump housing. The mouth of the air channel in the end-face area of the projection seals off the air channel, and the prevailing low pressure in the upstream chamber holds the projection against the end face, causing the air channel to remain closed. This function of the check valve effectively prevents air from the area in or under the sound-absorbing hood from getting back into the air outlet opening and thus into the pump housing. Only a small volume of the upstream chamber is sucked back into the air outlet opening by the low pressure that forms, until the projection makes contact with the end face and seals off the air channel. As soon as the vacuum pump is placed back into operation, the upstream chamber is again pressurized and the projection lifts back off from the end face of the pump housing and the air channel in the projection is cleared. As a result, the vacuum pump can continue to be used under normal operating conditions. 
     For example, the upstream sound absorber element has a diaphragm section in which the projection with the air channel is held, particularly in the center. In accordance with an advantageous embodiment, the upstream sound absorber element is shaped like a circular disk and has an outer ring section used to hold the upstream sound absorber element between the sound-absorbing cover and the end face of the pump housing. Thus the projection with the air channel in the center is located in the upstream sound absorber element, and the diaphragm section extends in the shape of a circular disc around the central projection with air channel. In this design, the upstream sound absorber element is advantageously designed as one piece, causing the projection to cross over into the diaphragm section in one piece. 
     The upstream sound absorber element also provides the additional advantage of a ring section and the diaphragm section is advantageously formed between the projection and the ring section. As such, the ring section can stabilize the upstream sound absorber element, and the projection can move axially relative to the ring section like a speaker over the diaphragm section. The ring section also provides an advantage of crossing over into the diaphragm section as one piece and the ring section is also made of an elastic rubber material. 
     As another advantage, ribs are formed on the inside in the sound-absorbing cover; the upstream sound absorber element comes to rest against these ribs at least with the diaphragm section if the vacuum pump is in operation. The ribs prevent the diaphragm section from creating a seal in the path of airflow because the diaphragm section cannot come into contact with the inside of the sound-absorbing cover. 
     As another advantage, a sealing lip is radially attached to the outside of the ring section and the lip is in contact with a circumferential ridge in the sound-absorbing cover. The design of the sealing lip forms another sound-absorbing space that is fluidly connected by a flow constriction to the ribbed chamber where the ribs are arranged. 
     As another advantage, a circumferential holder ridge is formed in the sound-absorbing cover with the ring section of the upstream sound absorber element being held by that ridge. A flow constriction can also be provided in the holder ridge in the effective connection with the ring section, causing the air to pass through this flow constriction when it goes from the ribbed chamber into an intermediate space formed in the area above the sealing lip. 
     Another advantage is that the air channel in the projection has a cross-section that is dimensioned with such a small size that an air-regulating effect is created when air flows through the air channel between the upstream chamber and a ribbed chamber formed between the upstream sound absorber element and the sound-absorbing cover. 
     The advantage from the inventive sound damping of the vacuum pump results from combining the sound-absorbing action with the function of a check valve. Another advantage stems from the several successively formed air regulating chambers, which are each achieved through flow constrictions and are arranged in the flow path in sequence. This achieves a particularly effective sound-damping effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made more particularly to the drawings, which illustrate the best presently known mode of carrying out the invention and wherein similar reference characters indicate the same parts throughout the views. 
         FIG. 1  is a perspective view of a vacuum pump with a cross-sectional sound-absorbing cover and a cross-sectional upstream sound absorber element. 
         FIG. 2  is a view of the vacuum pump in accordance with  FIG. 1 , where the air flow path is shown indicating how the air flows through and around the upstream sound absorber element. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a vacuum pump  100  with a primarily cylindrical pump housing  10 , in which a rotor with slider elements is mounted to swivel, where the vacuum pump also has an electric motor connected on the bottom of the pump housing  10  but not described in greater detail here. 
     The pump housing  10  has a primarily cylindrical design and has an end face  10   a  at the top and two air outlet openings  11  are shown in the end face  10   a  as an example. 
     The cylindrical pump housing  10  is surrounded by a sound-absorbing cover  12 , and the air that flows out of the air outlet openings  11  goes into a gap space  13  formed all the way around between the cylindrical pump housing  10  and the bowl-shaped sound-absorbing cover  12 . 
     In the area above the pump housing  10  between the end face  10   a  and the bottom area of the bowl-shaped sound-absorbing cover  12 , an upstream sound absorber element  14  made of an elastic rubber material is inserted. An upstream chamber  15  is formed between the end face  10   a  and the upstream sound absorber element  14 ; the air from the air outlet openings  11  initially flows into this chamber to work together with the upstream sound absorber element  14  as described below. 
     If the vacuum pump  100  is taken out of operation, air flows out of the air outlet openings  11  into the upstream chamber  15 . The upstream chamber  15  is bounded radially on the outside by an outer ring section  19  of the upstream sound absorber element  14  tensioned between a holder ridge  23  of the sound-absorbing cover  12  and the end face  10   a  of the pump housing  10 . In this configuration, ring section  19  forms a seal on the end face  10   a . Through the sealing effect, the air entering into the upstream chamber  15  from the air outlet openings  11  goes through an air channel  17 , which is installed in a central projection  16  in the upstream sound absorber element  14 . Once the air has passed through the air channel  17 , it goes into a ribbed chamber  24  formed between the upstream sound absorber element  14  and the bottom area of the bowl-shaped sound-absorbing cover  12 . 
     In the ribbed chamber  14 , several ribs  20  extend outwards radially and the ribs  20  are on the inside. Sound-absorbing cover  12  arranged. The elastic rubber upstream sound absorber element  14  is at the front sides of the ribs  20  during vacuum pump  100  operation, allowing the air to flow outward radially between the ribs  20 . 
     Cavities are provided between the ring section  19  and the holder ridge  23  at two points provided as examples and not shown in greater detail here; this allows the air to go into an intermediate space sealed against another ridge  22  by a sealing lip  21 . The ridge  22  is arranged on the inside of the sound-absorbing cover  12  and has several slits  25  in its circumference, allowing the air to ultimately go through the slits  25  into the gap space  13 . 
     The upstream sound absorber element  14  has a diaphragm section  18  that extends between the projection  16  and the ring section  19 . If the vacuum pump  100  is taken out of operation, low pressure is abruptly created in the upstream chamber  15  because air is sucked back into the pump housing  10  through the air outlet openings  11 . The projection  16  moves against the end face  10   a  and comes to rest against it. The air channel  17  is subsequently sealed and no air can flow back into the air outlet openings  11 . This function forms a check valve and the projection  16  does not lift off of the end face  10   a  and uncover the air channel  17  until the vacuum pump  100  has resumed operation. The check valve function created in this way prevents the ingress of dirt into the air outlet openings  11  because no contaminated air can flow back into the upstream chamber  15  due to the sealed air channel  17 . This advantageous embodiment of the upstream sound absorber element  14  eliminates the need for the placement of a filter, allowing a reduction in flow resistance for the outflow of air out of the air outlet openings  11  due to the elimination of the filter. 
       FIG. 2  shows the vacuum pump  100  with the pump housing  10  and with the sound-absorbing cover  12  shown in cross-section; arrows are used to indicate the flow paths taken by the air out of the air outlet openings  11  to go into the gap space  13 . 
     The upstream chamber  15  forms an initial air regulating chamber II into which the air flows from the air outlet openings  11 , as indicated by the arrows. Subsequently, the air goes through the air channel  17  into a second air regulating chamber II formed by the ribbed chamber  24 . 
     The cross-section provides a view of a cavity between the ring section  19  and the holder ridge  23 ; it shows that the air flows into another air regulating chamber III from the ribbed chamber  24 , with the air regulating chamber being bounded on the bottom by a sealing lip  21 . 
     Due to several slits  25  distributed around the circumference of the additional ridge  22 , the air ultimately goes into a circumferential gap space  13 , which forms another, final air regulating chamber IV. 
     The formation of several air regulating chambers I-IV arranged in succession, each with its own choke cross-sections between air regulating chambers I-IV, achieves especially advantageous sound dampening. 
     The design of the invention is not limited to the preferred embodiment specified here. Rather, a number of variants are conceivable, which make use of the present solution also in designs of a fundamentally different type. All of the features and/or advantages arising from the claims, description or drawings, including design details, physical layout and process steps, may be vital to the invention both by themselves and in a wide variety of combinations. 
     REFERENCE NUMERAL LIST 
     
         
           100  Vacuum pump 
           10  Pump housing 
           10   a  End face 
           11  Air outlet opening 
           12  Sound-absorbing cover 
           13  Gap space 
           14  Upstream sound absorber element 
           15  Upstream chamber 
           16  Projection 
           17  Air channel 
           18  Diaphragm section 
           19  Ring section 
           20  Rib 
           21  Sealing lip 
           22  Ridge 
           23  Holder ridge 
           24  Ribbed chamber 
           25  Slit 
         I Air regulating chamber 
         II Air regulating chamber 
         III Air regulating chamber 
         IV Air regulating chamber