Patent Publication Number: US-2009238707-A1

Title: Vane  pump

Description:
PRIOR ART  
     The invention relates to a vane pump as generically defined by the preamble to claim  1 . 
     A vane pump of this kind is known from DE 199 52 167 A1. This vane pump has a pump housing that contains a rotor, which is driven to rotate via a drive shaft. The rotor has a number of grooves distributed over its circumference that extend in an at least essentially radial direction in relation to the rotation axis of the rotor, each of which has a respective vane-shaped delivery element guided in it in sliding fashion. The pump housing has a circumference wall encompassing the rotor and extending eccentrically in relation to its rotation axis, against which the radially outer ends of the vanes rest. The pump housing has housing end walls situated adjacent to the rotor in the direction of the rotation axis of the rotor. Because of the eccentric arrangement of the circumference wall, the vanes form chambers, which expand and contract during rotation of the rotor and between which the medium to be supplied is conveyed with an increase in pressure from a suction region to a pressure region that is offset from it in the circumference direction. Centrifugal forces when the rotor is turning hold the vanes in contact with the circumference wall, but at low speeds, particularly when vane pump rotation is just starting, only slight centrifugal forces are exerted so that the vane pump only delivers a small amount. In the known vane pump, another delivery pump that forms a combined pump unit with the vane pump supplies the inner regions, which are delimited in the grooves by the vanes, with compressed medium, which presses the vanes outward toward the circumference wall in addition to the centrifugal force. In this case, at least one housing end wall is provided with an annular groove extending over part of the circumference of the rotor, which is supplied with compressed medium by the additional delivery pump. The annular groove is separated from the drive shaft by a sealing region in which the rotor and the adjoining housing end wall are situated spaced slightly apart from each other in the axial direction. The annular groove is situated concentric to the rotation axis of the rotor so that the sealing region has a constant radial span. The disadvantage in this known vane pump is that the annular groove extending over only part of the circumference of the rotor only exerts pressure on the inner regions of the grooves of the rotor over a corresponding part of a rotation of the rotor, as a result of which under some circumstances, there is only a slight pressing force of the vane against the circumference wall. Moreover, the sealing region can permit leakage of pressurized medium from the annular groove toward the drive shaft. 
     ADVANTAGES OF THE INVENTION 
     The vane pump according to the invention, with the characteristics according to claim  1 , has the advantage of the prior art that the exertion of pressure on the inner regions of the grooves of the rotor is intensified by means of the annular groove extending over the entire circumference of the rotor. In addition, by means of the eccentricity of the annular groove in relation to the rotation axis of the rotor the sealing region between the annular groove and the drive shaft, it is possible to intentionally enlarge the radial span of the sealing region in a circumference region of the rotor, which can be used to reduce the leakage from the annular groove. 
     Advantageous embodiments and modifications of the vane pump according to the invention are disclosed in the dependent claims. 
    
    
     
       DRAWINGS 
       An exemplary embodiment of the invention is shown in the drawings and will be explained in detail in the subsequent description. 
         FIG. 1  shows a simplified view of a vane pump in a cross section along the line I-I in  FIG. 3 , 
         FIG. 2  shows the vane pump in a cross section along the line II-II in  FIG. 3 , and 
         FIG. 3  shows the vane pump in a longitudinal section along the line III-III in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENT 
       FIGS. 1 through 3  show a vane pump that is preferably provided for delivery of fuel, in particular diesel fuel. In this instance, the vane pump delivers fuel from a tank to a high-pressure pump. The vane pump can be separate from the high-pressure pump, built onto the high-pressure pump, or integrated into the high-pressure pump. The vane pump has a pump housing  10  that is comprised of multiple parts and a drive shaft  12  that protrudes into the pump housing  10 . The pump housing  10  has two housing end walls  14 ,  16  that delimit a pump chamber in the axial direction, i.e. in the direction of the rotation axis  13  of the drive shaft  12 . In the circumference direction, the pump chamber is delimited by a circumference wall  18  that is integrally joined to the housing end walls  14 ,  16  or can be embodied as a component separate from them. 
     As shown in  FIGS. 1 and 3 , the pump chamber contains a rotor  20  that is attached in a torsionally fixed manner to the drive shaft  12 , for example by means of a groove/spring connection  22 . The rotor  20  has a plurality of grooves  24  distributed over its circumference, extending at least essentially radially to the rotation axis  13  of the rotor  20 . The grooves  24  extend into the rotor  20  from the outer circumference of the rotor  20  toward the rotation axis  13 . For example, four grooves  24  are provided; it is also possible for fewer or more than four grooves  44  to be provided. In each groove  24 , a plate-shaped delivery element  26  is situated in sliding fashion, which will be referred to below as a vane and whose radially outer end region protrudes out from the groove  24 . Each vane  26  delimits an inner region  25  situated toward the radial inside in the respective groove  24 . 
     The inside of the circumference wall  18  of the pump housing  10  is situated eccentrically to the rotation axis  13  of the rotor  20 , for example in the form of a circle or some other shape. In at least one housing end wall  14 ,  16 , as shown in  FIG. 2 , a suction region is provided, which communicates with at least one suction opening  28 . The suction opening  28  connects to the suction groove  30 , preferably in its end region oriented opposite the rotation direction  21  of the rotor  20 . The suction opening  28  is connected to an inlet leading from the tank. At least one housing end wall  14 ,  16  is also provided with high-pressure region, which communicates with at least one pressure opening  32 . In the pressure region, preferably in at least one housing end wall  14 ,  16 , an elongated pressure groove  34  is provided, which is curved in an approximately kidney-shaped fashion, extends in the circumference direction of the rotor  20 , and communicates with the pressure opening  32 . The pressure opening  32  connects to the pressure groove  34 , preferably in its end region oriented in the rotation direction  21  of the rotor  20 . The pressure opening  32  is connected to an outlet that leads to the high-pressure pump. The suction opening  28 , the suction groove  30 , the pressure opening  32 , and the pressure groove  34  are situated spaced radially apart from the rotation axis  13  of the rotor  20 , close to the inside of circumference wall  18 . The radially outer ends of the vanes  26  rest against the inside of the circumference wall  18  and slide along it in the rotation direction  21  as the rotor  20  turns. Because of the eccentric design of the inside of the circumference wall  18  in relation to the rotation axis  13  of the rotor  20 , the vanes  26  form chambers  36  with changing volumes. The suction groove  30  and the suction opening are situated in a circumference region in which the rotating motion of the rotor  20  in the rotation direction  21  causes the volume of the chambers  36  to increase so that they are filled with fuel. The compression groove  34  and the pressure opening  32  are situated in a circumference region in which the rotating motion of the rotor  20  in the rotation direction  21  causes the volume of the chambers  36  to decrease so that fuel is displaced from them into the pressure groove  34  and from there into the pressure opening  32 . 
     In at least one housing end wall  14 ,  16 , as shown in  FIG. 2 , an annular groove  38  is provided, which extends over the entire circumference of the rotor  20  and communicates with the pressure groove  34  via a connecting groove  40 . In lieu of the connecting groove  40 , it is also possible for a connecting bore to be provided. Between the annular groove  38  and the drive shaft  12 , a sealing region  39  is formed in which there is only a slight axial distance between the rotor  20  and the adjoining housing end wall  14 ,  16 . In the region around the drive shaft  12 , there is only a slight amount of pressure so that between the annular groove  38  and the region around the drive shaft  12 , there is a pressure difference. The annular groove  38  extends eccentrically in relation to the rotation axis  13  of the rotor  20  so that the radial span s of the sealing region  39  is different over the circumference of the annular groove  38 . The annular groove  38  can, for example, be at least approximately circular, having a center point M, which is situated offset from the rotation axis  13  of the rotor  20  by a distance e that constitutes the eccentricity. Preferably, the eccentricity e of the annular groove  38  is at least approximately of the same magnitude and oriented in the same direction as the eccentricity of the inside of the circumference wall  18  of the pump housing  10 . Preferably, the center point M of the annular groove  138  is situated offset from the rotation axis  13  in a direction toward a region of the circumference wall  18  situated between the suction groove  30  and the pressure groove  34  in the rotation direction  21  of the rotor  20 . This eccentric arrangement of the annular groove  38  increases the radial span s 1  of the sealing region  39  inside the annular groove  38  in relation to the drive shaft  12  on the side toward which the center point M is offset in relation to the rotation axis  13  while decreasing the radial span s 2  of the sealing region  39  on the opposite side. It is also possible for the annular groove  38  to not be circular, but to have an eccentric course in relation to the rotation axis  13 , in which case the radial span s 1  of the sealing region  39  in a region between the suction groove  30  and the pressure groove  34  in the rotation direction  21  of the rotor  20  is greater than the radial span s 2  of the sealing region  39  in the opposite region. 
     The connecting groove  40  can, for example, extend inward from the pressure groove  34  in a radial direction or at an angle to a radius with regard to the rotation axis  13 . The connecting groove  40  can, in particular, extend in such a way that it approaches the annular groove  38  in the rotation direction  21  of the rotor  20 . In addition, the connecting groove  40  can extend in a spiral curve. The connecting groove  40  is preferably connected at one end at least approximately tangentially to the pressure groove  34  and/or at the other end, at least approximately tangentially to the annular groove  38 . Preferably, the connecting groove  40  connects to the end region of the pressure groove  34  oriented opposite from the rotation direction  21  of the rotor  20 . As a result of the connection of the annular groove  38  to the pressure groove  34 , an increased pressure prevails in the annular groove  38  and therefore in the inner end regions of the grooves  24  of the rotor  20  with which it communicates, which increases the contact force with which the vanes  26  rest against the inside of the circumference wall  18 , thus improving the delivery capacity of the vane pump. The curved course of the connecting groove  40  also generates a drag flow in it as the rotor  20  turns, resulting in a further pressure increase in the annular groove  38  and therefore in the grooves  24 , thus further increasing the contact force of the vanes  26  against the circumference wall  18 . In particular, this drag flow achieves a pressure increase in the annular groove  38  even when the vane pump rotation is just starting so that the vane pump delivers a sufficient quantity of fuel even as it is starting to turn. The curved course of the connecting groove  40  also assures that when the rotor  20  is turning, the vanes  26  move across the connecting groove  40  in an approximately tangential fashion, which minimizes the wear on the vanes  26  and the housing end wall  14 ,  16 . 
     It is possible for the annular groove  38  and the connecting groove  40  that connects it to the pressure groove  34  to be provided in only one housing end wall  14  or  16  or for an annular groove  38  and a connecting groove  40  to be provided in both housing end walls  14  and  16 , which grooves are then preferably situated in mirror-image fashion in relation to each other in the housing end walls  14  and  16 . It is also possible for a respective annular groove  38  to be provided in each of the two housing end walls  14  and  16 , but for a connecting groove  40  to be provided in only one housing part  14  or  16 . It is also possible for the suction groove  30  and/or the pressure groove  34  to be provided in only one housing end wall  14  or  16 , in which case the other housing end wall  16  or  14  is embodied as smooth or for a respective suction groove  30  and/or pressure groove  34  to be provided in each of the two housing end walls  14  and  16 , which grooves are then preferably situated in mirror-image fashion in relation to each other in the housing end walls  14  and  16 . In this case, however, the suction opening  28  and the pressure opening  32  are each provided in only one respective housing end wall  14  or  16 , with the suction opening  28  provided in one housing end wall  14  and the pressure opening  32  provided in the other housing wall  16 . With the mirror-image arrangement of the suction grooves  30  and pressure grooves  34  and of the annular grooves  38  and connecting grooves  40  in the two housing walls  14  and  16 , the rotor  20  and the vanes  26  are loaded in at least approximately equal fashion at both ends in the axial direction so that little or no resulting force is exerted on the rotor  20  and the vanes  26  in the direction of the rotation axis  13 . For example, the depth of the annular groove  38  and connecting groove  40  in the housing end wall  14 ,  16  is between 0.1 and 2 mm and the width of the grooves  38 ,  40  is preferably greater than their depth.