Abstract:
A positive-displacement pump including a rotating vane disposed within a pump housing. The rotating vane is driven by a rotating drive shaft and the rotating vane is radially displaceable relative to the drive shaft wherein the ends of the rotating vane carry sealing strips that adjoin an inner wall of the pump housing. At least one energy storage device is included for engaging the vane and holding the sealing strips in sealing contact with the housing.

Description:
TECHNICAL FIELD 
     The invention generally relates to pumps, and more particularly relates to a positive-displacement pump with a vane for mutually separating the two chambers in the interior of the pump housing. 
     BACKGROUND OF THE INVENTION 
     A positive-displacement pump of this type is already known from FIG. 2A of DE 41 07 720 A1. In this case, both end faces of the vane that separates the two chambers of the pump housing interior from one another and is guided in a restricted fashion respectively carry one sealing strip that is movably guided in the longitudinal direction of the vane and adjoins the inner circumferential wall of the housing interior. 
     In order to realize this movable arrangement of the sealing strips, they are realized with a T-shaped cross section, with the cross section of the outside of the T-bar being convexly curved and consequently contacting the circumferential wall along only one surface line. 
     The central web of the strip is engaged with a longitudinal groove machined into the end face of the vane such that it can be moved in the longitudinal direction of the vane, so that the sealing strips automatically adjoin the inner circumferential wall of the housing when the drive shaft rotates due to the effect of centrifugal force. 
     The disadvantage of this construction can be seen in the fact that the sealing strips only adjoin the inner circumferential wall of the housing interior in a sealing fashion due to the centrifugal force once a certain rotational speed of the drive shaft is reached. This means that a chamber seal which ensures a reliable transport of the gaseous or aqueous medium is not realized until this time. 
     Positive-displacement pumps of this type consequently are, for example, not suitable for evacuating a brake booster of a motor vehicle since an evacuation needs to be ensured at slow rotational speeds in this case. 
     The present invention is based on the objective of disclosing a positive-displacement pump, in which a transport of the respective medium starts at a rotational speed&gt;0 or when the centrifugal force during the start of the motor-driven pump does not yet suffice for displacing the sealing strips of the vane into their maximum radial sealing position. 
     Due to the fact that the vane is equipped with an energy storing device, a permanent contact of both sealing strips with the circumferential wall of the housing interior is also ensured while the shaft is at a standstill, so that the respective medium is displaced or transported at the beginning of the shaft rotation. 
     In this context, it should be mentioned that FIG. 4 of DE 41 07 720 A1, which was cited above with reference to the state of the art, discloses a pump construction, in which the vane is already equipped with energy storing devices in the form of compression springs. In contrast to the construction according to the invention, the sealing strips are immovably held on the vane ends, i.e., the compression springs do not serve for holding the sealing strip in constant contact with the inner circumferential wall of the housing interior, but rather for supporting the end of the vane that moves into the lower dead center in the oval housing interior in order to compensate for the effects of centrifugal force (see column 5, lines 5 ff.). 
     According to one advantageous embodiment of the invention, the vane may be guided such that it can be radially displaced on the drive shaft or in a pump rotor that is driven by said drive shaft. In this case, it may, as mentioned above, already suffice to merely arrange one energy storing device between the vane and one of its sealing strips. However, it is preferred to arrange both sealing strips such that they can be moved in the longitudinal direction of the vane, with both sealing strips being supported by one respective energy storing device. 
     The movable arrangement of the sealing strips may be realized in accordance with FIG. 2A of DE 41 07 720 A1. In this case, the energy storing devices may be respectively arranged between the base of the vane groove and the web of the T-shaped cross section of the sealing strips. 
     One preferred arrangement of the movable sealing strips on the vane makes it possible to eliminate mold slides for forming guide grooves on the end face of the slide vane as well as on the strip during the injection molding of the vane and the sealing strips. In addition, the sealing strips that are attached to or overlap the vane end in this construction have a higher stability because the bending moments during the vane rotation which result from radial support forces can be favorably absorbed by the U-limbs of the sealing strips. 
     The energy storing device that is realized in the form of a leaf spring can be advantageously positioned such that the vane and the sealing strips simultaneously remain exactly aligned relative to one another in the lateral direction. 
     An alternative arrangement of the energy storing device is disclosed wherein this construction is primarily advantageous if the interior of the pump housing has a shape that highly deviates from a circular cylindrical circumference and the sealing strip or strips need to be displaced by relatively large radial distances during the rotation of the vane. 
     Another advantageous vane construction is disclosed wherein the sealing strips are arranged on the vane ends such that they can be moved in the longitudinal direction of the vane. 
     It should also be mentioned that the invention can be utilized in an equally advantageous fashion on the vane of vane-cell pumps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, a partially sectioned representation of a positive-displacement pump with a pump rotor that contains a vane realized in accordance with the invention; 
     FIG. 2, a longitudinal section through the rotor vane according to FIG. 1; 
     FIG. 3, a longitudinal section through one variation of the rotor vane; 
     FIG. 4, a view of a longitudinal vane edge; 
     FIG. 5, a view into the interior of a positive-displacement pump, the vane of which represents another embodiment of the invention; 
     FIG. 6, a side view of a positive-displacement pump according to FIG. 5, and 
     FIG. 7, a perspective representation of the pump vane that is formed by two partial vane elements. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The positive-displacement pump according to FIG. 1 conventionally contains a pump housing  10 , a pump rotor  16  that is eccentrically arranged in the, for example, circular cylindrical interior  12  of the pump housing and connected to the drive shaft  14  in a rotationally rigid fashion as well as a rotor vane  18  that is guided in a radially movable fashion in said pump rotor and carries one respective sealing strip  20  and  22  on its vane ends. 
     The pump rotor  16  preferably contains a hollow cylindrical rotor casing  24 , in which an inner vane guide strip  26  that extends along its inside diameter is provided. The rotor vane  18  is accommodated in this vane guide strip such that it can be radially displaced. The reference symbol  28  identifies inner rotor webs for reinforcing the rotary casing. The rotor  16  is slotted toward the drive shaft  14  in order to guide the vane  18  and attached, inserted or integrally injection-molded into/onto the shaft  14 . 
     Although not shown in the figures, the housing interior  12  is tightly sealed on both end faces, with the drive shaft  14  extending through one end face of the housing in a fluid-tight fashion. An inlet line and an outlet line are also connected to the housing interior  12  in order to supply and discharge a medium to be conveyed by the positive-displacement pump. 
     The sealing strips  20 ,  22  of the rotor vane  18  preferably have a U-shaped cross section, with the U-limbs  30 ,  32  respectively overlapping a guide web  34  that preferably is integrally formed onto the vane end faces over the entire width of the vane. In order to achieve an exactly linear relative movement of the sealing strips  20 ,  22  in the longitudinal direction of the rotor vane  18 , the sealing strips are preferably equipped with two guide elements  36 ,  38  that are laterally spaced apart and extend parallel to one another. These guide elements are integrally formed onto the spine  40  that connects the U-limbs  30 ,  32  and extend parallel thereto, with the length of said guide elements preferably being smaller than that of the U-limbs  30 ,  32 . 
     The guide elements  36 ,  38  respectively engage depressions  42  and  44  that are realized similar to blind holes and thusly also ensure an exact alignment of the sealing strips  20 ,  22  perpendicular to the longitudinal direction of the vane. 
     The spine  40  of the sealing strips  20 ,  22  which connects the U-limbs preferably has such a cross section that it simultaneously defines a sealing edge  46  on the outer side. In order to constantly hold this sealing edge in a sealing contact with the inner circumferential wall of the housing interior  12 , an energy storing device that is preferably realized in the form of a leaf spring  48  is provided between the guide web  34  of the vane and the spine  40  of the strip. This energy storing device constantly displaces the respective sealing strip  20  or  22  in the direction of the inner circumferential wall of the housing interior  12  and holds the respective sealing strip in contact with this inner circumferential wall. 
     In an alternative variation, one respective compression spring  50  and  52  may, for example, be arranged in each depression  42 ,  44 , with the strip guide elements  36 ,  38  being supported on said compression springs (FIG.  3 ). 
     The rotor vane  18  as well as the sealing strips  20 ,  22  are preferably realized in the form of injection-molded plastic parts, with the rotor vane  18  being provided, for example, with three recesses  54  that are realized in the form of flat slots and transversely extend through the rotor vane parallel to its flat sides, in particular, to achieve a uniform material distribution during the injection molding process. The pump rotor  16  may also be centrally arranged in the housing interior  12  if the latter has an oval circumferential shape. 
     The positive-displacement pump according to FIGS. 5 and 6 contains a flange body with a cylindrical pot  62  that forms a pump housing  61 , a pump drive shaft  63  that is arranged in the pump housing and contains an attached rotor  64  and a two-part vane that is identified by the reference symbol  65  and guided in a recess that extends over the rotor center. FIG. 7 shows that this vane is preferably formed by two flat, symmetrically stepped partial vane elements  65 ′,  65 ″ which respectively contain a pivot bearing on their outer end. A sealing strip  66  is arranged on this pivot bearing such that it can be pivoted about an axis that extends parallel to the rotational axis of the rotor. 
     The other end of the partial vane elements  65 ′,  65 ″ is designed in such a way that the elements are engaged with one another in a symmetrically, half-lap, flush fashion (see FIG. 7) or in the form of a tongue-and-groove arrangement (see FIG.  5 ). 
     Although not shown in the figures, a suitable compression spring needs to be positioned within the partial vane element  65 ″ in the latter instance. In the former instance, a Z-shaped spring  67  is arranged between the two partial vane elements  65 ′,  65 ″ as shown in FIG. 7, wherein the end faces of the elements are respectively supported on one limb of the Z-shaped spring. This spring moves the two partial vane elements  65 ′,  65 ″ apart from one another such that the sealing strips  66  contact the inner circumference of the cylindrical pot  62  with a defined force. 
     The sealing strips  66  have a concave radius  68  toward the wall of the cylindrical pot  62  (FIG.  5 ). This results in two contact lines  69  and  70  that serve for sealing the chambers in front and behind the vane  65  in cooperation with the flat partial vane elements  65 ′,  65 ″. Radii  71  and  72  are provided on the ends of the sealing strips  66  such that an optimal subsequent sealing effect is achieved. 
     The rotor  64  is slotted toward the drive shaft  63  in order to guide the vane  65  and is attached, inserted or injection-molded into/onto the shaft  63 . 
     During the rotation of the drive shaft  63 , the two partial vane elements  65 ′,  65 ″ are able to radially move in the rotor  64  independently of one another. The ends ( 69  and  70 ) of the sealing strips  66  adjoin the inner circumference of the cylindrical pot  62  at any rotational angle and thusly change their angle of contact relative to the translational axis of the vane  65 . Due to the fact that the sealing strips  66  are fixed in the pivot bearings of the partial vane elements  65 ′,  65 ″ and the fact that their angle of contact changes when the drive shaft  63  rotates, the axial distance between the two pivot bearings becomes variable in addition to the variable geometric size of the theoretical axial dimension in the vane axis when the sealing strips  66  adjoin the inner circumferential surface of the cylindrical pot  62 . 
     This length change is compensated by the radial mobility of the partial vane elements  65 ′,  65 ″. The adaptation to the variable length in the respective angle of rotation is realized by pressing the sealing strips  66  against the inner circumferential surface and driving the vane  65  by the drive shaft  63  via the spring  67  or a corresponding compression spring that presses the partial vane elements  65 ′,  65 ″ apart from one another and consequently presses the sealing strips  66  connected to these partial vane elements against the wall of the cylindrical pot. 
     The rotor vane  18 ;  65 , the partial vane elements  65 ′,  65 ″, the sealing strips  20 ,  22 ;  66  and the rotor  28 ;  64  can be advantageously manufactured from metal, plastic, ceramic, a metal-plastic combination, a metal-ceramic combination, a metal-plastic-ceramic combination or a plastic-ceramic combination. 
     With respect to plastic materials, polyether ether ketone (PEEK), polyether sulfide (PES), syndiotactic polystyrene (SPS) and polyphenylene sulfide (PPS) are preferably utilized.