Abstract:
A centrifugal precipitator having a housing and a rotatable driven rotor for precipitating oil mist from crankcase ventilation gas of an internal combustion engine. The housing has an inlet for gas to be deoiled, a deoiled gas outlet and an oil outlet. The housing includes a metallic main element surrounding the rotor and carrying the rotor bearing. A housing bottom is built onto the main element from below. The housing attaches with a flange to a counterflange or module of the engine. The housing flange is formed on the main element and the housing. The oil outlet runs through a first flange part of the housing bottom and this flange part has a circumferential rim. A second flange part of the main element has a collar engaging over part of its periphery behind the rim and can be clamped with the rim in between against the counterflange.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the German patent application No. 10 2011 076 465.8 filed on May 25, 2011, the entire disclosures of which are incorporated herein by way of reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a centrifugal precipitator for precipitating oil mist from the crankcase ventilation gas of an internal combustion engine, the centrifugal precipitator having a housing, a drivable rotor mounted rotatably therein, and a rotational drive for the rotor, the housing having a crude gas inlet for crankcase ventilation gas that is to be deoiled, a pure gas outlet for deoiled crankcase ventilation gas, and an oil outlet for oil precipitated from the crankcase ventilation gas, the housing having a multipart construction with a main element that surrounds the rotor and that holds the bearing thereof, having a housing cover containing the rotational drive, and having a housing floor built onto the main element from below, through which at least the oil outlet runs, and the housing being capable of being mounted by a flange onto a counterflange of the associated internal combustion engine or of a module forming part of the associated internal combustion engine. 
     A centrifugal precipitator of the type indicated above is known from WO 2010/951 994 A1. Here it is essential that the centrifugal precipitator has an electric motor as a rotor drive and has means for cooling the electric motor, at least one cooling element preferably being provided as a means for cooling the electric motor. Preferably, the housing has a lower part having an inlet for crude gas that is to be supplied for the rotor, and having an outlet for oil precipitated from the crude gas, the lower part being capable of being produced as a separate individual part, and being capable of being connected to the rest of the housing in various rotational positions relative thereto, preferably by welding or by being plugged together. The centrifugal precipitator can be equipped with a connecting flange with which it can be flange-mounted onto a module base, in particular of an oil filter module, or onto a cylinder head cover of the internal combustion engine, some or all of the required flow connections from and to the internal combustion engine running through the connecting flange. 
     In this known centrifugal precipitator, it is regarded as disadvantageous that it has a relatively heavy weight, because in order to achieve the necessary mechanical stability its housing is made up to the largest possible extent of metal, in particular aluminum. Due to the complex routing of the crude gas, pure gas, and precipitated oil inside the precipitator, it is necessary for the housing to have a multipart construction. Such a housing made of a plurality of metal parts is relatively expensive to manufacture, in particular if various connection interfaces, such as connecting pieces and flanges, are present in and on the housing, which have to be processed separately by machining, which is expensive. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to create a centrifugal precipitator of the type named above that avoids the indicated disadvantages and that has as low a weight as possible with high mechanical stability, and that can be produced economically and installed easily. 
     According to the present invention, this object is achieved by a centrifugal precipitator of the type named above that is characterized in that the flange is fashioned on the main element and on the housing floor, and that the oil outlet runs through a flange part allocated to the housing floor, and this flange part has a circumferential rim, and that a flange part allocated to the main element has a collar that engages behind the rim over at least a part of its circumference and that can be clamped against the counterflange with interposition of the rim. 
     The present invention advantageously brings it about that the carrying off of the oil precipitated from the crankcase ventilation gas during operation of the centrifugal precipitator is accomplished easily and along the shortest possible path. In addition, it is particularly advantageous that for the clamping of the flange part allocated to the housing floor, the flange part, allocated to the main element, of the common flange is used. This makes the attachment of the precipitator to the internal combustion engine or to the module particularly simple. The flange part of the housing floor is relieved of clamping forces for the flange connection. All clamping forces are received by the flange part allocated to the main element. The flange part of the housing floor is passively clamped with its rim between the collar and the counterflange. Because the main element on the one hand and the housing floor on the other hand are individual parts that can be manufactured separately, these can be made of different materials, and in particular a lighter material can be used for the housing floor than for the main element, contributing to a lower weight of the precipitator as a whole. 
     A particularly low weight is achieved if the housing floor, including its flange part with the circumferential rim, is made of plastic. In addition, given the use of a suitable plastic a separate flange seal can here be done without, because the material of the housing floor itself then forms the seal. 
     If the plastic of which the rim is made is not suitable for use as a sealing material, or if a particularly high degree of security against leakage is desired, then it is usefully provided that a seal is situated between the rim and the counterflange, in order to ensure the leak tightness of the flange connection. This seal can be for example an elastomer ring. 
     A preferred development proposes that the flange part allocated to the housing floor has an outline whose basic shape is rectangular, and that the collar has a fork shape, open at one side, and engages the rim from behind at at least two of its four sides. In this way, the engagement of the collar of the main element with the rim of the housing floor can be produced particularly easily, and can easily be detached as needed. 
     Here, it is further provided that the collar is open at its side that is the lower side in the installed position of the precipitator, and that the housing floor, for its connection with the main element, can be placed onto the main element from the open side of the collar, parallel to the plane of the flange. With this embodiment, a particularly simple connection of the main element and housing floor is achieved, because at the same time as their connection to one another the collar is also brought into its proper position for engagement with the rim. 
     A particularly advantageous and rapid assembly results if the main element and the housing floor have sealing elements that work together and are mutually axially and/or radially sealing, and the housing floor can be clamped axially against the main element by a central screw. 
     Due to the fact that the crude gas inlet preferably runs through the housing floor, a further savings of weight is possible, because the main element can then be realized more easily and simply. 
     In order to avoid an undesirable flow of gas through the oil outlet against the direction of oil flow, it is provided that a check valve is situated in the housing floor, in the course of the oil outlet. The check valve always closes the oil outlet when pressure conditions are present under which the mentioned undesirable gas flow could occur. 
     The centrifugal precipitator according to the present invention is suitable, inter alia, for truck engines. In many known truck engines, a main oil filling port is accessible only after tilting the driver cab forward, which is laborious. In order to remedy this, the present invention provides that an oil refill channel runs through the housing floor that can be connected on the one hand to an external oil filling port, and on the other hand is connected in terms of flow to the segment of the oil outlet running through the flange part. When the centrifugal precipitator is put in place and is connected to the external oil filling port, accessible from outside the truck, a refilling of smaller quantities of oil, the so-called daily oil filling, into the internal combustion engine is advantageously possible through the oil filling port and through the housing floor of the centrifugal precipitator, without the driver&#39;s cab having to be tilted for this purpose. 
     The present invention further provides that the collar has an inward-pointing pressure rib whose side facing the flange, in the state in which the housing floor is installed on the main element, is seated on the side of the rim of the housing floor facing away from the flange. Here, the side of the pressure rib facing the flange is at a distance from the flange plane such that, in the state where the precipitator is clamped against the counterflange, the rim of the housing floor is pressed against the counterflange with sufficient force, but not excessively strongly. Here, the collar simultaneously surrounds the rim radially externally at least over a part of its circumference, so that in the clamped state the rim cannot escape there in the direction of the flange plane. 
     In particular for reasons of rapid and simple installation of the precipitator on the associated internal combustion engine, or the associated module, the present invention further provides that in the collar there is made a plurality of bores for clamping screws for attaching the precipitator to the counterflange, and that when the housing floor is installed on the main element, imaginary axial prolongations of the bores run away in the direction of the flange, external to the housing floor. The introduction of the clamping screws into the bores and the use of screwdriving tools is therefore not prevented by the housing floor. 
     In order to ensure an operationally reliable and long-lasting sealing tightness of the flange connection between the precipitator on the one hand and the internal combustion engine or module on the other hand, the present invention further proposes that the collar be fashioned as a three-dimensional structure having reinforcing webs running in various directions. Through the fashioning indicated here of the collar, the collar becomes inherently particularly rigid and therefore capable of bearing high mechanical loads, and warpage of the collar, resulting in lack of leak tightness of the flange connection, is avoided. 
     For an effective precipitation of oil mist, in particular fine and very fine oil particles, from the crankcase ventilation gas, a high rotational speed of the rotor is essential. In order to achieve this, the rotational drive for the rotor is preferably formed by an electric motor. 
     Finally, the present invention proposes for the centrifugal precipitator a crankcase pressure regulating valve that is situated in the run of the pure gas outlet and is connected to the housing or built into the housing. In this way, with small outlay of constructive space and assembly, a further function necessary for the operation of the associated internal combustion engine can be integrated into the centrifugal precipitator. 
     As mentioned above, the main element and the housing floor are individual parts that can be manufactured separately, offering the advantageous possibility of producing each component from a separate functionally appropriate material. The main element is usefully made of a more stable material, such as metal, so that it can accept higher mechanical loads resulting in particular from the rotation of the rotor with a high rotational speed and from the clamping against the counterflange. The housing floor is not subject to these mechanical loads, so that it can be made, without disadvantages, of a plastic that is less stable but is advantageously lighter and lower in cost. At the same time, the plastic material offers the advantage that the housing floor inherently has a certain movability that is useful for compensating dimensional tolerances during the connection of the housing floor to the main element on the one hand and to the counterflange on the other. 
     Particularly preferably, the main element is a pressure die-cast part made of light metal, in particular aluminum. In this embodiment, the main element is on the one hand capable of accepting mechanical loading, but on the other hand is nonetheless relatively low in weight and is capable of being produced at very low cost as a mass-produced part. 
     Particularly preferably, the housing floor is an injection-molded part made of thermoplastic, in particular polyamide (PA). This material is well suited for the mechanical and thermal loads that occur, and has low weight and advantageous material costs. Advantageously, in plastic injection molding the housing floor, with all necessary connections, can be produced in one piece off-tool, i.e. without post-processing. In this way, a low-cost production of the housing floor as a mass-produced part is also possible. 
     In addition, through the production of various housing floors and through the installation of the various housing floors on identical main elements, different embodiments of the centrifugal precipitator having different connections can be realized with a low outlay, thus making available an advantageous modular system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, an exemplary embodiment of the present invention is explained on the basis of a drawing. 
         FIG. 1  shows an oil mist precipitator with a housing floor not yet attached, in a perspective view, 
         FIG. 2  shows the oil mist precipitator of  FIG. 1  with attached housing floor, in the same view as in  FIG. 1 , 
         FIG. 3  shows the oil mist precipitator of  FIG. 2  with attached housing floor, in a view of its side having a connecting flange, 
         FIG. 4  shows the oil mist precipitator of  FIGS. 2 and 3  in a vertical longitudinal section, and 
         FIG. 5  shows the oil mist precipitator of  FIGS. 2 and 3  in a state attached to a counterflange, in a horizontal cross-section at the level of the housing floor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The upper part of  FIG. 1  of the drawing shows, in a perspective view, a centrifugal precipitator  1  having a housing  10 , and the lower part of the Figure shows an associated housing floor  6  not yet connected to the rest of centrifugal precipitator  1 . 
     Centrifugal precipitator  1  has housing  10 , which forms a main element  5  of precipitator  1 . At the upper side, housing  10  is sealed by a cover  7  that is detachably connected to housing  10  by screws  76 . Cover  7  here forms a cooling element for an electric drive of a centrifugal rotor (not visible here) situated in the interior of housing  10 . For the supply of electric energy, cover  7  has, on its side facing the observer, a power connection  41 , here in the form of a connecting socket. 
     At the side of housing  10  pointing to the right, there is situated a crankcase pressure regulating valve  9  whose housing is made at least partly integrally with housing  10  of centrifugal precipitator  1 . On crankcase housing pressure regulating valve  9  there is situated a pure gas outlet  12 , here in the form of a hose connection piece through which crankcase ventilation gas purified in centrifugal precipitator  1  leaves centrifugal precipitator  1 , and is preferably guided to the intake tract of an associated internal combustion engine. 
     On its lower side, housing  10  of centrifugal precipitator  1  is still open toward the top in the representation shown in  FIG. 1 . In a central part of the lower region of housing  10 , there is situated a lower bearing for centrifugal rotor  2  (not shown here). A central threaded bore  55  is directed downward and accepts a central screw for fastening housing floor  6  to the rest of housing  10 . 
     On the side of centrifugal precipitator  1  facing away from the observer, on the main element  5  thereof there is provided a flange part  50  that is formed essentially by a fork-shaped collar  51  that is situated in a vertical plane and is downwardly open. On its inward-pointing edges, collar  51  is fashioned with a pressure rib  52 . A plurality of bores  54  are provided in collar  51  that accept fastening screws with which centrifugal precipitator  1  can be clamped against a counterflange (not shown here) on an internal combustion engine, for example on the engine block thereof, or on a module forming part of the internal combustion engine. Further bores  54 ′ for clamping screws are situated in the upper part of main element  5 . 
     In order to complete the assembly of centrifugal precipitator  1 , housing floor  6  is moved upward in the vertical direction. In this way, housing floor  6  comes into sealing engagement with housing  10 . For the sealing, floor  6  has on its upper edge a circumferential sealing annular groove  69  into which a sealing ring (not shown here) can be placed. As a counterpiece thereto, housing  10  has, on its lower inner circumferential region, an annular sealing surface  59 . A bore  66  runs centrally through floor  6 , and a central screw (not shown here) can be guided through this bore into threaded bore  55 . 
     On its side facing the observer in  FIG. 1 , housing floor  6  has a flange part  60  that is limited by a circumferential rim  65 . Through this flange part  60  there runs an oil outlet  13  through which, during operation of centrifugal precipitator  1 , oil precipitated from the crankcase ventilation gas can be led out from precipitator  1 , in particular into the oil pan of the associated internal combustion engine. 
     When housing floor  6  is attached to the rest of centrifugal precipitator  1 , flange part  60  of floor  6  is guided into flange part  50  of main element  5  from below, after which fork-shaped collar  51  of flange part  50  then engages rim  65  of flange part  60  from behind. 
     Housing floor  6  here has two connections, namely a crude gas inlet  11  through which crankcase ventilation gas that is to be deoiled can be introduced into centrifugal precipitator  1 , as well as an oil refill channel  67  that can be connected to an external oil filling port (not shown here). 
     In  FIG. 2 , housing floor  6  is connected to the rest of centrifugal precipitator  1 . In order to connect the two parts to one another, central screw  56  is now guided through floor  6  from below and is screwed to housing  10 . Collar  51  of flange part  50  now engages rim  65  of flange part  60  from behind over its entire axial height. 
     With regard to the further parts and reference characters in  FIG. 2 , reference is made to the description of  FIG. 1 . 
       FIG. 3  shows centrifugal precipitator  1  of  FIG. 2 , now in a view of its rear side on which flange parts  50  and  60  lie. 
     In the upper part of  FIG. 3 , main element  5  with housing  10  and upper cover  7  and fastening screws  76  thereof are visible. At left at  FIG. 3 , crankcase pressure regulating valve  5 , with pure gas outlet  12 , is visible. 
     In the lower part of  FIG. 3  there is situated the flange of precipitator  1 , made up of the two flange parts  50  and  60 . Here, of housing floor  6  only flange part  60  thereof can be seen; in the region thereof, somewhat in the background, there is situated a check valve  64 . The function of check valve  64  is explained further on the basis of  FIG. 4 . 
     Flange part  60  has circumferential rim  65  in or on which there is situated a circumferential sealing ring  65 ′. 
     On its left, upper, and right edge, flange part  60  is engaged from behind in the region of its rim  65  by downwardly open fork-shaped flange part  50 , or more precisely by collar  51  thereof. Here, pressure rib  52  of collar  51  is situated behind rim  65 , as can be seen in particular at the lower edge of flange part  60 . 
     Opposite flange part  60 , offset outward, bores  54  are situated in flange part  50 . Two further fastening bores  54 ′ for the assembly of centrifugal precipitator  1  are situated in the upper region thereof 
       FIG. 4  shows a centrifugal precipitator  1  of  FIGS. 2 and 3 , in a longitudinal section. The central region of centrifugal precipitator  1  is formed by the main element  5  thereof with housing  10 . In the interior thereof, there is situated centrifugal rotor  2 , formed here by a stack of conical plates  20 . Rotor  2  is situated on a shaft  3  so as to be secure against rotation, and the shaft is rotatably mounted in a first, upper bearing  31  and in a second, lower bearing  32 . A bearing seat for upper bearing  31  is situated in a metallic sleeve in housing cover  7 , and the lower bearing is situated in a metallic sleeve in main element  5 , the sleeves preferably being made of steel. Both housing cover  7  and main element  5  are preferably pressure die-cast parts made of light metal such as aluminum or magnesium. 
     At the top, housing  10  is sealed in gas-tight fashion by cover  7 , sealing ring  79 ′ being situated between housing  10  and cover  7  for this purpose. Cover  7  has a rotational drive  4 , here in the form of an electric motor  40 , for centrifugal rotor  2 . At the upper left in  FIG. 4 , connecting socket  41  is visible for the supply of electric energy to motor  40 . 
     Housing  10 , which at first is downwardly open, of main element  5  is sealed by housing floor  6 , which is pushed into main element  5  from below in the axial direction, and is fastened by central screw  56 , screwed into threaded bore  55 . For mutual sealing, there is a sealing ring  69 ′ that is placed into sealing ring groove  69  of floor  6  and that works together in sealing fashion with sealing surface  59  of main element  5 . 
     At the right in  FIG. 4  there is situated the flange with flange parts  50  and  60 , to which centrifugal precipitator  1  can be connected, mechanically and in terms of flow for the precipitated oil, to the associated internal combustion engine or to a module belonging to the internal combustion engine. Sealing ring  65 ′ provides the seal for this connection. 
     At lower left in  FIG. 4 , oil refilling channel  67  is visible, in the form of a connecting port. 
     During operation of centrifugal precipitator  1 , a crankcase ventilation gas that is to be deoiled flows through crude gas inlet  11 , situated in front of the sectional plane, first into a crude gas annular channel  61  in housing floor  6 , and from there in the axial direction upward into the radial inner region of centrifugal rotor  2  situated in a gas purification chamber  14 . Through the rotation thereof, the gas, loaded with oil droplets, is accelerated outward in the radial direction, causing the oil droplets carried along in the gas to precipitate onto the surfaces of plates  20 . Due to centrifugal forces, the collected oil droplets are accelerated onto the inner circumference of housing  10 , where an oil conducting insert  15  ensures that the centrifuged oil is conducted downward. 
     The deoiled gas leaves gas purification chamber  14  through pure gas outlet  12  (not shown in  FIG. 4 ). The precipitated oil flows on the inner surface of oil conducting insert  15  downward into an oil collecting channel  63  formed integrally on housing floor  6  and upwardly open, which is radially outwardly sealed relative to main element  5  by sealing ring  69 ′ and is radially inwardly sealed relative to main element  5  by a sealing lip  69 ″ injection-molded onto housing floor  6 . If corresponding pressure conditions are present, the oil runs through check valve  64  into oil outlet  13 , which runs through flange part  60 . Check valve  64  is always open when a greater pressure prevails on the side of oil collecting channel  63  than on the side of oil outlet  13 . If, under certain operating conditions of the associated internal combustion engine, a higher pressure is present in oil outlet  13  than in oil collecting channel  63 , check valve  64  then closes and prevents an undesired flow of gas through oil outlet  13  into gas purification chamber  14 . 
       FIG. 5  shows centrifugal precipitator  1  of  FIGS. 2 through 4  in a horizontal cross-section at the level of housing floor  6  and of flange  50 ,  60 . In the center of  FIG. 5 , central screw  56 , screwed into threaded bore  55 , is sectioned. At the left and right thereof there runs crude gas annular channel  61 . In  FIG. 5 , crude gas inlet  11  opens from below into crude gas annular channel  61 . 
     At the left in  FIG. 5 , oil refilling channel  67  is visible, connected in terms of flow to oil outlet  13 . When centrifugal precipitator  1  is installed on an internal combustion engine, oil refilling channel  67  is connected to an outer oil filling port (not shown here) that is used to refill smaller quantities of oil, the so-called daily oil filling, to the internal combustion engine. Here it is not required that the main oil filling port, which is often situated so as to be covered, be made accessible, which would require for example a tilting forward of the driver cab of a truck. 
     In the region of oil outlet  13 , a part of oil collection channel  63  can be seen, which is connected in terms of flow to oil outlet  13  via check valve  64 . 
     In  FIG. 5 , flange parts  50  and  60  of main element  5  and housing floor  6  are situated on the right side of centrifugal precipitator  1 , and are here shown in a state in which they are connected to a counterflange  8 . Counterflange  8  can for example be situated immediately on the engine block of an associated internal combustion engine or on a module, belonging to the associated internal combustion engine, that contains further components. An oil outlet channel  83 , which usefully leads to the oil pan of the associated internal combustion engine, runs through counterflange  8 . In the region of flange part  50 , reinforcing webs  53  thereof are partly visible. 
     In addition to oil outlet  13 , one or more further channels can also be guided through flange parts  50  and  60  and through counterflange  8 , e.g. for crude gas inlet  11  and/or for pure gas outlet  12 . 
     Flange part  60  is a part of housing floor  6 , and in the depicted example contains oil outlet  13 . On its outer edges, which here describe a rectangle, flange part  60  has rim  65 , which bears sealing ring  65 ′ on its side pointing toward counterflange  8 . 
     Flange part  50  is a part of main element  5 , which is made of metal, and with its collar  51  engages rim  65  of housing floor  6  from behind, the housing floor usefully being a plastic part. In this way it is achieved that when clamping screws are screwed through bores  54  into threaded bores  85  in counterflange  8 , flange part  50  presses flange part  60  against counterflange  8  and clamps it there in gas-tight and liquid-tight fashion. Here, flange part  60  does not require any clamping screws of its own. The dimensions of rim  65  and of collar  51  are matched to one another in such a way that rim  65  is pressed against counterflange  8  with sufficient force and sealing tightness, but without risk of damage. 
     As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art. 
     LIST OF REFERENCE CHARACTERS 
     
         
           1  centrifugal precipitator 
           10  housing 
           11  crude gas inlet 
           12  pure gas outlet 
           13  oil outlet 
           14  gas purification chamber 
           15  oil conducting insert 
           2  rotor 
           20  plate 
           3  shaft 
           31  first bearing 
           32  second bearing 
           4  rotational drive 
           40  electric motor 
           41  power connection for  40   
           5  main element 
           50  flange part on  5   
           51  collar 
           52  pressure rib 
           53  reinforcing webs 
           54  bores in  50   
           54 ′ bores at top in  5   
           55  central threaded bore in  5   
           56  central screw 
           59  sealing surface for  69 ′ 
           6  housing floor 
           60  flange part on  6   
           61  crude gas annular channel 
           63  oil collection channel 
           64  check valve 
           65  rim on  60   
           65 ′ sealing ring in  65   
           66  central bore in  6   
           67  oil refilling channel 
           69  sealing ring groove 
           69 ′ sealing ring in  69   
           69 ″ sealing lip on  6   
           7  housing cover 
           76  screws 
           79 ′ sealing ring on  7   
           8  counterflange 
           83  oil outlet channel in  8   
           85  threaded bores in  8   
           9  crankcase pressure regulating valve