Abstract:
A vane for a vane cell pump, in particular a vacuum pump, including: a vane body, wherein the vane body has an opening on at least one end-facing side facing a cover or base of a pump space of the vane cell pump; and an insert which is arranged in the opening and guided such that it can be axially moved in the opening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 10 2014 107 735.0 filed Jun. 2, 2014, the contents of such application being incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a vane for a vane cell pump, preferably a vacuum pump, wherein the vane comprises an opening on at least one of its end-facing sides facing a cover or base of a pump space of the vane cell pump, wherein an insert is arranged in the opening which is pressed against the cover and/or base by means of a tensing device. The invention also relates to a vane cell pump, comprising: a pump body made of a first material having a first coefficient of expansion; and a vane made of a second material having a second coefficient of expansion which is different to the first coefficient of expansion. Lastly, the invention relates to a method for increasing an evacuating output of a vacuum pump at low and/or higher temperatures. 
       BACKGROUND OF THE INVENTION 
       [0003]    In order to save weight and cost, but also from a tribological viewpoint, metal materials are more and more frequently being replaced with plastics, including in the manufacture of pumps. The vane of a vacuum pump can for example be formed from a plastic, while the pump body and therefore also the pump chamber consists of a metal, for example aluminium. The two materials being used together in this case generally exhibit different coefficients of expansion. This can lead to deviations in the dimensions of the two parts when the pump is heated or cooled, which at least compromise the separation between the suction side and the pressure side in the pump space, since the oil which is otherwise used for sealing is no longer sufficient to reliably seal the gap. 
         [0004]    On the other hand, component part tolerances which are inevitable and/or permissible in terms of production can be equalised by intelligently using materials having different coefficients of expansion. This can mean that the produced parts need not exhibit a minimum producible degree of tolerance, which can be achieved only at great expense, in order to nonetheless securely and reliably establish a necessary strength of seal. The reduced production expense enables cost savings, for example due to simpler production or fewer rejects. 
       SUMMARY OF THE INVENTION 
       [0005]    An aspect of the invention provides a vane for a vane cell pump, a vane cell pump and a method for sealing a vane cell pump in its pump space which do not exhibit the aforementioned disadvantages. 
         [0006]    Other embodiments of the invention are respectively the subject of the sub-claims. They can be combined with each other in any technologically expedient way, wherein features of the sub-claims can, where expedient, be combined across categories with any of the independent claims. The description, in particular in connection with the drawings, additionally characterises and specifies the invention. 
         [0007]    In accordance with a first aspect, the invention relates to a vane for a vane cell pump, in particular a vacuum pump. The vane comprises a vane body made of plastic and/or metal which comprises an opening on at least one end-facing side facing a cover or base of a pump space of the vane cell pump. An insert is arranged in the opening and guided such that it can be axially moved. A tensing device which is for example arranged in the vane body biases the insert towards the base or the cover. 
         [0008]    The tensing device can bias the insert axially towards the base or the cover of the pump space. 
         [0009]    When the vane is installed, the insert forms an axial sealing gap with the axially facing base or cover, i.e. with a respective end-facing surface of the pump space, and thus reduces leakage losses on the end-facing side of the vane on which the insert is arranged. The terms “axial” and “axially” refer to the rotary axis of a rotor of the vane cell pump and denote a direction or extension parallel to said rotary axis. The rotor can guide the vane such that it can be moved translationally in a direction transverse to the rotary axis. Alternatively, the vane can be fastened to the rotor, for example such that it can be pivoted. The opening in which the insert is arranged axially faces the cover or the base of the pump space. 
         [0010]    The insert can likewise be manufactured from plastic and/or metal or at least comprise parts made of a plastic. It can consist of multiple layers and/or multiple separate or connected parts. The insert can thus for example comprise a base body which is formed from a plastic, and a metal film or a varnish which forms a surface of the insert can be applied to the base body. The insert can however also consist of multiple layers and can be formed integrally or be original-moulded in one piece from one material as a compact body. 
         [0011]    The material can be one with low elastic deformability, no or only very little attrition and good sliding properties, which can be optimally adapted to the shape of an inner surface of the base or cover, thereby generating as far as possible no frictional forces or only very small frictional forces which slow a rotation of the vane. The shape of the insert can also be selected such that the insert only touches the base or cover linearly, for example by rounding or acuminating the surface facing the cover or base. The end-facing side(s) of the vane can thus exhibit a wedge-shaped gap geometry for conveying a hydraulic lubricating pressure build-up, in order to prevent mixed frictional states from occurring during operation. The aim is to reduce friction between the end-facing side of the vane and the radial inner wall of the pump chamber and/or to reduce the wear on at least one of the sliding surfaces on the vane or the radial wall of the pump chamber. 
         [0012]    Alternatively, the insert can be formed from a material with no elastic deformability. The abutting surface of the insert for abutting the base or cover can also be formed in the shape of a lip, comprising at least one straight lip or at least a circumferential lip, wherein the at least one circumferential lip encloses a region which can for example accommodate lubricant of the pump or fluid to be conveyed, for example oil, for further reducing the frictional forces. 
         [0013]    In the region in which the insert engages the opening, the surfaces of the vane and/or the corresponding complementary surfaces in the interior of the opening can be coated in order to ensure that the insert slides in the vane body with as little resistance as possible. This engaging region can simultaneously form a guiding region in which the insert is guided, preferably narrowly, in the vane body in order to prevent the insert from tilting or bending while the pump is in operation. The insert itself can be a compact body or a hollow profile which can comprise reinforcing fins in order to increase the rigidity of the insert. The hollow profile and the reinforcing fins can be formed integrally, for example in an injection-moulding or sintering process. The surface which forms the outer side of the insert can then be coated or can be provided with a suitable surface while still in the die. 
         [0014]    The insert can also comprise a form of wear monitoring, for example a conductive layer, which generates corresponding information, for example in a central computer of an automobile, in good time before the insert reaches a critical thickness, for example due to attrition, wherein said information can then be read off at the next inspection. 
         [0015]    The vane can be formed from a metal but is preferably formed from a plastic. The plastic can in particular be a polymer. The plastic can be a fibre-reinforced or otherwise reinforced plastic. 
         [0016]    In one embodiment, the vane or vane body can comprise an opening on each of said end-facing sides. An insert can then be respectively arranged in each of the openings. The vane body between the two openings can in particular be formed as a hollow body. The hollow body can comprise reinforcing fins in its interior for stabilising, which prevent the hollow body from being deformed or collapsing under the pressure of the fluid to be conveyed. The reinforcing fins can be linearly extending fins which are arranged parallel to each other and/or which intersect at a right angle or for example form a honeycomb structure. The reinforcing fins can be formed separately from the vane body and subsequently inserted into the vane body and connected to it. Alternatively, the reinforcing fins can be formed in one piece or original-moulded together with the vane body. The vane body, with or without the reinforcing fins, can also be constructed from two half-shells which are connected to each other in a positive fit, a force fit and/or a material fit after the shaping process and/or after the tensing device and/or insert(s) has/have been installed. The vane body can also be rigidified by spacers, in the form of pillars, instead of fins. Alternatively or additionally, the structure of the vane can exhibit geometries which guide, fix and/or position the tensing device and/or inserts relative to the vane. Additionally or alternatively, the side(s) which lead and/or trail in the rotational direction of the vane can exhibit a stabilising shape, for example a corrugated shape comprising sinusoidal, rectangular, triangular or serrate corrugations. 
         [0017]    The tensing device can comprise at least one spring element or can be formed by a pressure applying device which applies a pressure fluid to the insert. A cylinder which is filled with gas and comprises a piston can for example serve to apply pressure fluid to the insert, or the pressure fluid can be channelled from the pressure side of the pump into the interior of the vane. The pressure fluid can alternatively be provided by another unit of for example an internal combustion engine or a separate source. 
         [0018]    The spring element can consist of a solid body with elastic deformability or can comprise at least a leaf spring, spiral spring or other pressure spring. In order to ensure that the insert is pressed uniformly over its axial length onto the cover or base, it is in particular possible to arrange two, three or more spring elements adjacently and/or sequentially. 
         [0019]    The respective spring element can in particular be a pressurised helical spring. The vane body can comprise a guiding structure which, if the respective spring element is embodied as a helical spring, surrounds or protrudes through the respective spring element and thus supports it transverse to the axial direction and restricts the possibility of it yielding transverse to the axial direction. The guiding structure can in particular be a guiding sleeve. The guiding structure can be an insert element or can be formed directly by the vane body. 
         [0020]    If the vane comprises an insert on each end-facing side, each of these inserts can comprise a separate tensing device which is supported on a structure of the vane at its end pointing away from the insert. Alternatively, the two inserts can be jointly biased in their respective direction by a common tensing device, i.e. in this case, the tensing device is arranged between the two inserts in the vane body and is supported on both inserts. 
         [0021]    If the vane comprises an insert on each of the two axial end-facing sides, the above statements made with respect to one insert apply equally to the other insert. 
         [0022]    In the latter case in particular, the tensing device can be fixedly connected to both inserts, such that the tensing device and the inserts form a component part which can be inserted in its entirety into the vane through one of the openings. 
         [0023]    The vane body can in particular surround the at least one opening or the respective opening and therefore also the insert or the respective insert. 
         [0024]    The vane body can guide the insert or the respective insert such that it can slide axially. The insert or the respective insert can in particular be guided, such that it can slide axially, on an inner circumferential surface of the vane body which forms the respective opening. The surfaces which are in guiding engagement with each other—the surfaces of the respective insert on the one hand, and the inner circumferential surface of the vane body on the other hand—can in particular form a sealing gap with each other. The sealing gap preferably encircles the insert completely, i.e. over an angle of 360°. The respective insert can slide, in a tight fit, on the inner circumferential surface which axially guides it, in order to reduce leakage loss in the region of the sliding guide. 
         [0025]    The vane, which is formed for example from a plastic, can exhibit a wall thickness which is equal to or less than 1.5 mm, at least in the region in which the opening is formed in the vane. If the vane forms a hollow structure, as described above, then the vane can have a thickness of between 1 mm and 3 mm. In this case, the vane preferably exhibits a maximum local thickness of 2 mm, while the average thickness of the vane wall is less than 2 mm, particularly preferably less than 1.8 mm. 
         [0026]    The insert is in particular a sealing strip made of a solid material or a hollow structure which abuts the cover and/or base while the pump is in operation and reliably separates a pressure side of the pump from a suction side of the pump. Since the vane is fitted with the axially movable sealing strip(s) as described above, this reliable separation between the suction side and the pressure side is ensured even at higher temperatures of more than 50° C. 
         [0027]    While the medium to be pumped, such as for example oil, exhibits a lower viscosity as the temperature increases, the part comprising a material exhibiting a higher coefficient of thermal expansion—in this case, for example, the vane or vane insert made of plastic—can expand more than the pump chamber made for example of metal, i.e. the end-facing side of the vane and/or the insert “grow” relative to the pump chamber, thus pressing the end-facing side against the radial inner wall of the pump chamber with increasing pressure. This higher pressure generates higher frictional forces, thus slowing the vane. Since the insert can retract into the vane, said increasing pressure can be equalised, such that a contact pressure of the end-facing side on the inner wall of the pump chamber substantially exhibits a constant value, despite the changing temperature in the pump chamber. 
         [0028]    The same also applies if the coefficient of thermal expansion of the pump chamber is greater than that of the vane and/or insert. In this case, the contact pressure of the end-facing side on the radial inner wall of the pump chamber would decrease as the temperature increases, which would enable a gap to open between the wall of the pump chamber and the end-facing side of the vane, resulting in an overflow of medium from the pressure side to the suction side. In this case, the tensing device can press the vane or insert against the wall of the pump chamber, such that the contact pressure of the vane on the wall of the pump chamber remains substantially constant and the gap does not open when temperatures rise in the pump chamber, despite the different coefficients of thermal expansion. 
         [0029]    Another aspect relates to a vane cell pump, comprising: a pump body made of a first material having a first coefficient of expansion; and at least one vane made of a second material having a second coefficient of expansion which is different to the first coefficient of expansion. 
         [0030]    The vane comprises a vane body, comprising: at least one opening on an end-facing side facing a base or a cover of a pump space of the pump; and an insert which is arranged in (each of) the opening(s) and biased towards the base or the cover by means of at least one tensing device. 
         [0031]    The vane cell pump comprises a pump housing, a stator and a rotor. The stator can be at least partially formed by the pump housing and forms a pump chamber comprising an inlet and an outlet for the fluid to be pumped. The rotor is arranged in the stator, eccentrically with respect to a circumferential wall which surrounds the rotor, and can be rotated relative to the stator about a rotary axis. The stator can be formed directly by the pump housing or by an insert structure arranged in the pump housing. The pump space is or comprises the pump chamber. The pump space comprises: the circumferential wall which surrounds the rotor and the vane or vanes; an end-facing wall which is formed by the base of the pump space; and an end-facing wall which is formed by the cover, wherein the end-facing walls lie axially opposite each other and are axially assigned across the circumferential wall. 
         [0032]    A setting member can be arranged in the pump housing, such that it can be moved back and forth relative to the rotor, and can form the circumferential wall, in order to be able to alter the eccentricity between the circumferential wall and the rotor and therefore a specific delivery volume of the pump. 
         [0033]    The following treatment centres on a single-vane vacuum pump, which is advantageous with respect to ease of construction and degree of effectiveness. In principle, however, the vane design described can also be advantageously used in multi-vane pumps. 
         [0034]    The rotor comprises a shaft which is connected to at least one rotor vane or other vane. The vane comprises a side which leads in the rotational direction and a trailing side and four end-facing or side walls, two of which move on a running surface formed for example by a circumferential wall of the stator, while at least one of the other two end-facing sides abuts and progresses on a wall which laterally delineates the pump chamber, for example a base or a cover of the pump chamber, forming a seal at least to the greatest extent possible. This prevents the suction side of the pump from being shorted to the pressure side of the pump, which would make a change in the pressure of the fluid transported by the pump impossible. 
         [0035]    At the operating temperature of the pump, the coefficient of expansion of the vane can in particular be greater than the coefficient of expansion of the pump body. The pump body can thus for example consist of a metal such as aluminium, while the vane is produced from a plastic. 
         [0036]    The vane can in particular be the vane described above, wherein it is advantageous if the coefficients of expansion of the vane body and the insert are as equal as possible, so that a gap is not formed in the region in which the insert engages the vane body, through which the medium to be conveyed can enter the interior of the vane. 
         [0037]    The two different coefficients of expansion of the vane and the pump chamber housing have a particularly advantageous effect at higher temperatures of the fluid to be conveyed, for example 50° C. and more, since the faster expansion of the vane in this temperature range ensures that the vane abuts the base or cover tightly and securely. 
         [0038]    The vane cell pump can in particular be a vacuum pump, for example the vacuum pump of an automobile, which is driven by an internal combustion engine or a separate electric motor. The vacuum pump can for example serve to vent a brake or to supply another unit with a vacuum. 
         [0039]    Another aspect relates to a method for increasing an evacuating output of a vane cell pump comprising a pump body made of a first material having a first coefficient of expansion and at least one vane made of a second material having a second coefficient of expansion which is different to the first coefficient of expansion. 
         [0040]    At least one tensing device and at least one insert are then inserted into the vane. The vane, together with the tensing device and the insert, is then arranged, such that it can be rotated, in a pump space of the vane cell pump, such that the insert or inserts is/are pressed against a cover and/or a base of the pump space of the pump by the tensing device. Occurrent differences in expansion between the pump body and the vane are compensated for by the axially movable inserts, since the insert(s) is/are pressed onto the cover and/or base in a seal, even at low temperatures. This in particular applies even at temperatures below 50° C. 
         [0041]    It holds for the entire description and the claims that the expression “a(n)” is used as an indefinite article and does not limit the number of parts to one. Where “a(n)” is intended to have the meaning of “only one”, this will be understood by the person skilled in the art from the context or will be unambiguously disclosed by the use of suitable expressions such as for example “one”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    An example embodiment is described below in more detail on the basis of two drawings. Technical features essential to the invention which can only be gathered from the figures form part of the scope of the invention and can advantageously develop the invention, on their own or in any combination shown. 
           [0043]    There is shown: 
           [0044]      FIG. 1  a vane in a sectional view; 
           [0045]      FIG. 2  a view onto an insert. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]      FIG. 1  shows an embodiment of a vane  1  in accordance with the invention—in this case, in a sectional view through the vane  1 . The vane  1  comprises a vane body  2 . The vane body  2  comprises two end-facing sides  3 ,  4  which, when the vane is installed in a pump space of a vane cell pump (not shown), face a cover of the pump space and a base of the pump space, respectively. In order to reduce the wear on the rounded end-facing sides of the vane  1 , it can be expedient to provide them with a wearing layer and/or wearing structure made of a particularly resistant material. 
         [0047]    The end-facing side  3  of the vane body  2  comprises an opening  5  in which an insert  6  or a sealing strip  6  is guided such that it can be moved in the axial direction. In order to be able to automatically move the insert  6  at least partially into and out of the opening  5 , a tensing device  7 ,  8  is arranged in the interior of the vane body  2  and biases the insert  6  in the direction out of the opening  5 . The insert  6  can be pressed into the opening  5  against the force of the tensing device  7 ,  8 . 
         [0048]    In the example embodiment shown, the tensing device  7 ,  8  is formed by spring elements  7 ,  8 . The spring elements  7 ,  8  are spiral springs which can be surrounded by guiding sleeves or guided by a journal which is preferably made of plastic and protrudes into the spring element  7 ,  8  (not shown in  FIG. 1 ), in order to prevent the spring elements  7 ,  8  from yielding laterally under pressure. As an alternative to or in addition to the helical or spiral springs shown, leaf springs, wave ring springs, disc springs or the like (not shown) can also be used. 
         [0049]    The ends of the spring elements  7 ,  8  facing away from the insert  6  are supported on a reinforcing fin  9  of a reinforcing structure for the vane body  2 . Additional reinforcing fins  10  are shown which extend transverse to the reinforcing fin  9 . The vane body  2  can be formed as a hollow structure, at least in regions, and the reinforcing structure serves to prevent the vane body  2  from collapsing under pressure. 
         [0050]    The insert  6  can comprise a coating in the region in which it is or can be in engagement with the opening  5 , wherein said coating, together with a smooth surface of the inner walls of the opening  5  (with or without a coating) keeps a frictional value between the outer surfaces of the insert  6  and the inner walls of the opening  5  small. 
         [0051]    Though not shown in  FIG. 1 , it is possible for each of the two end-facing sides  3 ,  4  to comprise an opening  5 , in each of which an insert  6  is arranged. In this case, each of the two inserts  6  can be assigned a tensing device  7 ,  8  each, wherein the two tensing devices  7 ,  8  can be supported on the reinforcing fin  9 . Alternatively, the two inserts  6  can be biased towards the cover and the base, respectively, by one tensing device  7 ,  8  which in this case can be supported on the two inserts  6 . 
         [0052]      FIG. 2  shows the insert  6  in a plan view onto the vane  1 . The vane body  2  and/or wall of the vane body  2  which surrounds the opening  5  and forms a receptacle and guide for the insert  6  is shown. The insert  6  can be formed as a solid body or as a hollow profile. If it is formed as a hollow body, it can comprise reinforcing fins (not shown) in its interior which stabilise and rigidify the insert  6 . 
         [0053]    The insert  6  can be manufactured in one piece, for example in an injection-moulding process. The region of the insert  6  which abuts the cover or the base can comprise a coating which is for example harder and/or more attrition-resistant and/or exhibits better sliding properties than the plastic from which the insert  6  is injection-moulded. The four circumferential sides of the insert  6  and/or the surfaces of the inner walls of the opening  5  can comprise a corresponding coating, so that frictional forces between the outer sides of the insert and the inner walls of the opening  5  are kept small in a region in which the insert  6  engages the opening. 
         [0054]    A wall thickness of the vane body  2  in the region of the opening  5  should not exceed a value of 2 mm if the vane  1  is formed as a hollow body and comprises two inserts  6 . If the insert  6  is formed as a hollow profile body, the thickness of the profile wall is similar to the wall thickness, i.e. preferably exhibits a value of 1.5 mm or more. 
         [0055]    Although a number of possible improving embodiments have been disclosed in the preceding description, it will be appreciated that numerous other variants of embodiments exist through possible combinations of any of the technical features and embodiments mentioned and also any of the technical features and embodiments which are obvious to the person skilled in the art. It will also be appreciated that the example embodiments are to be understood merely as examples which in no way limit the scope of protection, applicability or configuration. The preceding description is instead intended to illustrate to the person skilled in the art a suitable way of realising at least one example embodiment. It will be appreciated that numerous changes with respect to the function and arrangement of the elements can be made to an example embodiment, without departing from the scope of protection disclosed in the claims and its equivalents. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  vane 
           2  vane body 
           3  end-facing side 
           4  end-facing side 
           5  opening 
           6  insert, sealing strip 
           7  tensing device, spring element 
           8  tensing device, spring element 
           9  reinforcing fin 
           10  reinforcing fin