Abstract:
A cooling and lubricating arrangement of tribological contact areas is disclosed. The arrangement includes tribological contact areas that slide over one another, of which at least one contact area has a surface contour with surface depressions in which a lubricant is stored. The surface contour forms a number of elongate grooves, the gap heights of which, at least in respect of respectively two adjacent grooves, are preferably different.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2010 054 416.7, filed on Dec. 14, 2010 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a rising arrangement for tribological contact areas for cooling and lubricating the latter and in particular to a rotary vane pump with an adjustable lifting ring, which is provided with a rinsing arrangement according to the disclosure. 
         [0003]    In principle, tribology examines friction, lubrication and wear of bearings, guides, gears, motors and other machine elements. In addition to developing suitable lubricants, questions in respect of material selection, surface coating and surface topography are at the forefront of current developments. In addition to questions from mechanical engineering, there are numerous further fields in which friction and wear are of great importance, for example in endoprosthetics. 
         [0004]    In the case of hydraulic machines such as e.g. rotary vane pumps, but also in the case of other machines with components that are in frictional contact, there is the basic problem of adhesive wear and abrasive wear resulting therefrom at so-called tribological contact points, particularly if a normal force acts on these contact points/areas and the latter merely move microscopically, i.e. only very little, with respect to one another, at least over a certain period of time. There is virtual dry operation at the contact point, in which the tribological partner “fluid” is barely or not at all present. As a result, there is overheating of the areas, coking of the possibly present remaining fluid, frictional corrosion and, not least, premature adhesive wear. Adhesive wear may also occur in the case of macro-movements where very much frictional heat is generated. 
         [0005]    A pump unit with a main pump and a charge pump, which has an adjustable delivery volume and is embodied as a rotary vane pump, is mentioned here as a user-related example, as known, inter alia, from the prior art, for example as per DE 10 2007 032 103 A1. 
         [0006]    This pump unit comprises an axial piston pump as the main pump, the rotary vane pump also being driven via the driveshaft thereof. Here, the rotor of the rotary vane pump is seated directly on the extended driveshaft of the main pump in a rotationally fixed fashion. Here both pumps are housed in a common housing. As an alternative, the rotary vane pump can also have its own driveshaft, which is coupled to the driveshaft of the main pump via a bushing, for example. 
         [0007]    A number of slits lying substantially in axial planes running parallel to the axis of the rotor have been introduced into the rotor of the rotary vane pump. Each slit holds a radially moveable pump vane, which rests against the internal wall of a lifting ring in a sealing fashion as a result of the centrifugal force, which occurs when the rotor rotates, and an occasionally additionally present restricted guidance and slides along said lifting ring. In respect of its relative position with respect to the rotational axis of the rotor, the lifting ring is, with the pump vanes, mounted in the housing in a displaceable fashion with respect to the radial direction in order thus to change the measure of eccentricity of the inner wall of the lifting ring with respect to the rotational axis, and hence to change the swept volume of the rotary vane pump. According to DE 10 2007 032 103 A1, the lifting ring is mounted externally in displaceable fashion in diametrically opposing parallel bearing areas on corresponding counter areas of the housing. The adjustment is brought about as a function of the output pressure of the rotary vane pump, wherein the pressure acts on an operative area on the lifting ring, determined by the spacing of the two bearing areas and the axial extent of the lifting ring, and acts against a spring. 
         [0008]    The ratio between guidance length and guidance width of the lifting ring in the pump housing is not very expedient in the known rotary vane pump. As this ratio decreases, the risk of jamming increases. This is linked to the lever length available to the frictional forces. 
         [0009]    In view of these circumstances, it is the object of the present disclosure in general to design so-called tribological contact areas such that the fictional forces are kept low. In particular, an increase in the frictional forces as a result of adhesive and abrasive wear to have and as a result of excessive heat influx should be kept low during operation. A particular goal of the disclosure is to improve the tribological contact areas between a lifting ring and its sliding partner in the case of a rotary vane pump such that the frictional forces, and hence the risk of the lifting ring jamming, are kept low. 
       SUMMARY 
       [0010]    This object is achieved by a rinsing arrangement for tribological contact areas, particularly on the lifting ring of a rotary vane pump and the sliding partners thereof, as per the features of patent claim  1 . Advantageous embodiments of the disclosure are the subject matter of the dependent claims. 
         [0011]    Accordingly, the disclosure provides for a rinsing arrangement of tribological contact areas, consisting of two tribological contact areas that slide over one another, wherein a number of grooves or groove sections are formed in at least one of the tribological contact areas. According to the disclosure, the surface contour forms a number of elongate grooves or groove sections, the gap heights of which in respect of respectively two adjacent grooves preferably differ. As an alternative or in addition thereto, the grooves can extend in labyrinthine fashion, wherein the general alignment of the grooves however should basically run in the movement direction of the surface-structured contact area. 
         [0012]    An embodiment in which the grooves run in a zigzagged or wavy form between the different pressure potentials appears particularly expedient. Here, the groove sections running at an angle to the movement direction are particularly helpful because, in the case of an adjustment movement, fluid is dragged out of the grooves into between the contact regions of the tribological contact areas. Here, the groove depth preferably alternates from groove to groove. 
         [0013]    The grooves, which act as gaps, interconnect at least two different lubricant pressure potentials that are spaced apart in the movement direction of the tribological contact areas. As a result, a pressure difference or pressure drop is created along the tribological contact areas. This effect can now be utilized by designing and/or aligning the grooves such that the pressure drop as it were leads to the lubricant jumping over the separating webs forming between the grooves, as a result of which dirt particles and abrasive particles adhering to the web surfaces (contact zone sections to the opposing contact area) are rinsed out of the fluid and, moreover, the webs are cooled and lubricated. In respect of the embodiment and/or alignment of the grooves, a number of options are proposed, which can be applied individually or in combination with one another: 
       1. Different Gap Heights of Respectively Adjacent (Adjoining) Grooves 
       [0014]    The flow through the gap is proportional to the 3rd power of the respective gap height. By contrast, the groove cross section is merely proportional to the 1st power of the gap height. It is for this reason that the quotient of through-flow to groove cross section (i.e. the lubricant speed) is very different compared to the respectively adjacent groove. The static pressure of the resting lubricant (liquid) at the higher pressure potential is reduced in the grooves by the dynamic pressure component, which in turn is proportional to the 2nd power of the above-defined lubricant speed. Accordingly, this results in significant static pressure differences to the respectively adjacent groove. 
         [0015]    It follows that the volume flows generated by the pressure differences between adjacent grooves pass over the separation or sealing webs between the respectively adjacent grooves, and hence the latter are lubricated, cooled and also cleaned. This avoids or at least improves both the primary adhesive and secondary abrasive wear (inter alia as a result of washing out dirt particles or decomposition products of the lubricant (e.g. coking, etc.) as well). 
         [0016]    The depth of the grooves and the depth difference is based on the requirements in respect of the volumetric losses and the cooling/lubricating dependent on the energy influx and the tendency for dry operation. 
       2. Reducing the Groove Spacing to a Minimum Dependent on the Maximum Permissible Surface Pressure 
       [0017]    It is advantageous if the number of grooves is increased up to a limit value (resulting from a surface pressure value that may not be exceeded) in order to install the lubrication/cooling in a uniform and finely distributed fashion. Moreover, more lubricant for cooling/lubrication will flow (leak out) over the thin sealing webs/ribs between the grooves resulting from this. 
         [0000]    3. Groove Profile Across the Movement Direction, at least in Sections 
         [0018]    Moreover, it is advantageous if the profile of the grooves is not, or not everywhere, aligned in the movement direction of the tribological contact areas (although, in principle, it goes without saying that this is also possible). Thus, the grooves can have a wavy shape, a zigzagged shape, a diagonal extent, etc. This carries lubricant over the support webs as a result merely of the relative movement and, moreover, the contradirectional partner (i.e. the opposing contact area) is not always covered at the same point. Here there also is a small flow over the web from one groove section to a subsequent groove section of the same groove because there is a pressure drop between successive groove sections of the same groove as a result of the pressure drop over the entire length of the groove. 
       4. Labyrinthine Groove Profile 
       [0019]    In this profile variant of the grooves there is a pressure difference or a pressure drop along each groove section merely due to the pressure drop when liquid respectively flows through the groove as a result of the hydraulic resistance caused by the groove. Since groove sections with different pressure levels respectively adjoin one another as a result of this, liquid passes over the support webs between the adjoining groove sections, as mentioned above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The disclosure will be explained in more detail below on the basis of preferred exemplary embodiments, with reference being made to the accompanying figures. 
           [0021]    In detail: 
           [0022]      FIG. 1  shows a view in the axial direction of the lifting ring of a rotary vane pump, which lifting ring is situated in a housing and the bearing areas (tribological contact areas) of which are, according to the disclosure, provided with grooves for rinsing, 
           [0023]      FIG. 2  shows a plan view of a tribological contact area with a surface profile as per a first exemplary embodiment, 
           [0024]      FIG. 3  shows a plan view of a tribological contact area with a surface profile as per a second exemplary embodiment, 
           [0025]      FIG. 4  shows a plan view of a tribological contact area with a surface profile as per a third exemplary embodiment, 
           [0026]      FIG. 5  shows a preferred cross-sectional shape for grooves which are formed into the tribological contact area as per  FIGS. 2 to 4 , and 
           [0027]      FIG. 6  shows the lifting ring from  FIG. 1  with one of the two bearing areas being visible. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    According to  FIG. 1 , on opposing sides of a lifting ring  6  of a rotary vane pump and on an elongate recess  12  in a housing  10 , in which the lifting ring is situated, there are two mutually corresponding guidance regions  8  and  9  on the lifting ring and guidance regions  14  and  15  on the housing. The housing  10  has a suction channel  21 , which opens into a suction kidney  22 , and a pressure channel  23 , which originates from a pressure kidney  24 . The guidance regions  8  and  9  on the lifting ring are formed by bearing areas (tribological contact areas) situated on the external circumference, which bearing areas run parallel to one another and parallel to a displacement axis  16  of the lifting ring  6  and are diametrically opposite to one another in the same direction as the two kidneys  22  and  24 . Accordingly, the guidance regions  14  and  15  on the housing are bearing areas (tribological contact areas), with these bearing areas having a greater extent in the direction of the displacement axis than the bearing areas on the lifting ring and so the bearing areas of the lifting ring fully lie thereon. In order to adjust the delivery volume of the rotary vane pump, a force, applied radially from the outside, in the direction of the displacement axis  16  is applied to the lifting ring  6 , as a result of which there is a change in the distance between the axis of the lifting ring  6  and the axis  18  of the rotor, not visible in  FIG. 1 , of the rotary vane pump. During the adjustment, the bearing areas  8  and  9  on the lifting ring  6  slide along the opposing guidance regions  14  and  15  on the housing  10 . Here there is a greater load on the bearing areas  9  and  15  because these are situated outside of the pressure kidney  24  and the pump pressure acts from the inside on the lifting ring  6  in the region of the pressure kidney  24 . 
         [0029]    According to  FIG. 2 , a tribological contact area, which is the bearing area  9  in the exemplary embodiment according to  FIG. 1 , in general has a number of grooves  2  spaced apart in parallel that basically extend along an intended movement direction of the tribological contact area  9 . Support or sealing webs  4 , which define a support area (-line) on their free upper edge, are formed between the grooves  2  and are in sliding contact with a contradirectional partner (opposing tribological contact area), which is not shown in any more detail in  FIG. 1 . In order to reduce the friction between the contact areas, provision is made for a preferably liquid lubricant, e.g. oil, which is applied to the contact areas or pressed therein. 
         [0030]    Here the assumption is made that, as seen in the movement direction of the tribological contact area  9 , the lubricant is under higher pressure on the one side of the tribological contact area  9  than on the other side of the tribological contact area  9 . Thus there is a pressure drop over the tribological contact area in the movement direction. 
         [0031]    According to  FIG. 2 , the design of the grooves  2  in the longitudinal extent is such that this results in groove sections that extend across or at an angle to the movement direction. In concrete terms, the grooves as per  FIG. 1  have a zigzagged shape along the movement direction. 
         [0032]    As a result of this shaping, groove sections of two directly adjacent grooves  2  adjoin one another, which groove sections lie behind one another as seen in the movement direction and thus have different partial pressure levels. These different pressure levels result in a flow over the sealing webs  4  separating the grooves  2 , as a result of which particles adhering to said webs are rinsed off and the contact areas are lubricated and cooled. This flowing-over occurs between adjacent grooves, and also, because there is a pressure drop between these groove sections, between groove sections of the same groove, which groove sections lie behind one another in the direction from higher to lower pressure potential and run at an angle to one another. 
         [0033]    Directly adjacent grooves  2  are preferably formed with groove depths that differ from one another. In the simplest variant, two different depth values are provided, which are distributed alternately to the respectively adjacent grooves and are preferably substantially constant over the whole length of the groove. However, reference is also made here to the fact that the respective groove depths may change along the groove (e.g. increase or decrease). 
         [0034]    In the embodiment according to  FIG. 3 , the grooves  2  are formed in a straight line and parallel to one another along the intended movement direction of the respective tribological contact area  9 . Since there is a uniform pressure drop along the contact area  9  in all grooves  2  in this case, there first of all is no pressure difference between two grooves  2  (90°) which are transverse to the movement direction. However, in this case the respectively adjacent grooves  2  are necessarily formed with groove depths that differ from one another, in accordance with the optional embodiment as per  FIG. 1 , as a result of which a pressure difference is respectively set locally in a (90°) transverse direction to the movement direction. The effect is the same as in the first exemplary embodiment. 
         [0035]    In the embodiment as per  FIG. 4 , the contour of the tribological contact area  9  exhibits a labyrinthine profile consisting of a groove  2 , which in the present case while forming right-angled bends extends sections that run parallel to one another over the tribological contact area  9 . Accordingly, in a manner comparable to the first preferred exemplary embodiment of the disclosure, this results in groove sections with respectively different sections lengths coming to rest directly behind one another when viewed in the movement direction, up to the front region in respect of the tribological contact area  9  with a higher pressure potential. However, there is a pressure difference between different groove sections because the groove sections are at different distances from the sides with higher and lower pressure potential. There is also a pressure drop between adjacent groove sections as a result of the different length of adjacent groove sections and hence differing gap lengths. Thus, rinsing liquid (lubricating fluid) flows over between both the groove sections running perpendicular to the movement direction and those running parallel to the movement direction. 
         [0036]    As a result of this, different pressure levels act upon adjacent groove sections directly behind one another, as seen in the movement direction, and so the same effect can be obtained as already described above on the basis of the first and the second exemplary embodiment. Moreover, in the case of a plurality of grooves, these can be formed with different groove depths. 
         [0037]    In this respect, reference is at this point made to  FIG. 5 , which illustrates a cross section of two directly adjacent grooves as per the preceding description. It is possible to gather from this that both grooves are formed with a partial-circle profile, with the two partial circles having the same radius. Meanwhile, the partial circle section of the one groove is greater than the partial circle section of the directly adjacent groove. This leads to the groove depth and in this case also the groove width of the two grooves being different to one another. Here, the depth of the deeper groove is 0.15 mm and the depth of the less deep groove is 0.10 mm. Hence the depth of the one groove is only ⅔ that of the other groove. In terms of the flow cross section, the grooves differ by a factor of between 3 and 5. 
         [0038]    As an alternative to this, it is of course also possible to embody the grooves with different radii or even with different cross-sectional shapes, with the latter optionally leading to different hydraulic resistances of the groove shapes. 
         [0039]    Finally,  FIG. 6  shows purely a lifting ring  6  as a practical application option of the rinsing arrangement according to the disclosure, as used in particular in rotary vane pumps as per e.g.  FIG. 1 . The lifting ring is guided between the bearing faces  14  and  15  of the housing  10  (see  FIG. 1 ) on the two diametrically opposing flattenings  8  and  9 . The two flattenings constitute two tribological contact areas. The flattening  9 , i.e. the flattening in the pressure region, is embodied as per the exemplary embodiment according to  FIG. 2 . It goes without saying that embodiments as per  FIG. 3  or  FIG. 4  are also possible. The flattening  8  can likewise also be provided with a rinsing arrangement for improving the cooling and lubrication. 
         [0040]    According to  FIG. 6 , the bearing areas on the lifting ring are equipped with the rinsing arrangement as per one of the preceding exemplary embodiments. However, in principle, the contradirectional partner on the side of the pump housing can exclusively or in combination with the lifting ring  6  have a rinsing arrangement as per the disclosure. 
         [0041]    The profile in a tribological contact area can be introduced by stamping, pressing, machining or else by means of lasers. The depth of the profile preferably lies in the region between 0.05 and 0.20 mm.