Patent Publication Number: US-8974207-B2

Title: Gear pump

Description:
BACKGROUND OF THE INVENTION 
     Gear pumps comprise, amongst other things, internal gear pumps and annular gear pumps in which a driving gearwheel runs eccentrically in the internal tooth system of an annular gear. Internal gear pumps, which are particularly suitable for providing high pressures, are used to deliver fluids, for example to deliver fuel to an internal combustion engine. 
     In the prior art, it is known to integrate internal gear pumps or annular gear pumps in an electronically commutated electric motor, with the rotor of the electric motor simultaneously being in the form of an annular gear of the internal gear pump or annular gear pump. 
     DE 10 2006 007 554 A1 describes a delivery pump which is integrated in an electric motor. The delivery pump comprises a first gearwheel and a second gearwheel. A delivery space is formed between the two gearwheels. The second gearwheel is mounted at its center on a mandrel. The first gearwheel is an external gearwheel and forms the rotor, the second gearwheel is an internal gearwheel which is carried along in the eccentric center of the first gearwheel. The first gearwheel comprises glued-in permanent magnets which are arranged in a manner distributed over the circumference. External magnetic field generators generate a circulating rotationally changing field which results in direct motorized tracking of the rotor. 
     However, mounting of the annular gear, which has to adopt the drive torque of the electric motor, is problematical in configurations of this kind. At the same time, the hydraulic forces of the internal gear pump have to be transmitted to the stator and further to the pump housing. 
     EP 1 600 635 A2 describes an internal gear pump which has a pump section with an internal rotor which is formed with teeth on its outer periphery. An external rotor has teeth which are formed on its inner periphery. Both rotors are accommodated in a housing. The external rotor, which is in the form of an annular gear, is mounted by means of specially shaped additional components in this case. 
     The solutions known in the prior art for mounting the annular gear in an internal gear pump or in an annular gear pump have a mechanically complicated design and are therefore structurally elaborate, complex and expensive in terms of production. 
     Therefore, it is necessary to provide a simple and cost-effective solution for mounting an annular gear for an internal gear pump or an annular gear pump. 
     SUMMARY OF THE INVENTION 
     The invention provides a gear pump for delivering a fluid, having an externally toothed gearwheel, which is rotatably mounted on a bearing pin, and an internally toothed annular gear which engage in a meshing manner for the purpose of generating a delivery effect and which are arranged in a housing together with an electrically commutatable stator, with the stator extending around the annular gear in a concentric manner and interacting with an annular magnet for the purpose of generating an electromotive force, with the annular magnet together with the annular gear executing a rotary movement for the purpose of generating the delivery effect, with the annular gear being mounted by a sliding bearing. A structurally simple and therefore cost-effective solution for mounting is provided by mounting the annular gear using a sliding bearing. 
     The annular magnet is preferably arranged between the stator and the annular gear. In this case, the annular magnet does not have the task of providing a sliding bearing. The tasks of a sliding bearing are advantageously adopted by other components of the internal gear pump and the annular gear itself. 
     In a yet further preferred embodiment, the annular magnet and the annular gear are connected to one another in a rotationally fixed manner. Therefore, a drive torque is transmitted from the rotating electromagnetic field to the annular magnet and further to the annular gear of the internal gear pump or annular gear pump. The annular magnet itself does not adopt a bearing function. Said bearing function is advantageously adopted by other components, preferably by the annular gear itself. 
     Further preference is given to the annular gear being produced from a non-magnetic material. This provides magnetic decoupling between the individual components. 
     According to a further preferred embodiment, the annular gear is mounted by an annular section which is formed at least on a surface, which is opposite the annular gear, in the form of a sliding bearing. 
     A second radial gap with a value of 0.1 to 0.5 mm is preferably formed between the stator and the annular magnet. 
     According to a further preferred embodiment, the annular section is integrally formed with the housing and projects radially inward from said housing. 
     According to yet a further preferred embodiment, the annular section is pressed or glued into the housing. 
     Preference is also given to mounting the annular gear by a disk-like element which has a bearing pin which projects from the disk-like element and which is accommodated in a cutout which is correspondingly provided in the housing. The surface of the bearing pin is preferably in the form of a sliding bearing. As an alternative, an inner wall of the recess can be in the form of a sliding bearing. In this embodiment, the fuel connections are to be produced in the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be described in greater detail below with reference to the appended drawings, in which: 
         FIG. 1  shows a section through an internal gear pump according to the prior art, 
         FIG. 2  shows a section through an internal gear pump according to one embodiment, 
         FIG. 3  shows a section through an internal gear pump according to a further embodiment, 
         FIG. 4  shows a section through an internal gear pump according to yet a further embodiment, and 
         FIG. 5  shows a plan view of the internal gear pump of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a section though an internal gear pump  1  according to the prior art. The internal gear pump  1  comprises a pair of gearwheels which comprises an internally toothed annular gear  2  and an externally toothed gearwheel  3 . The gearwheel  3  is arranged in a rotatable manner on a bearing pin  4  eccentrically with respect to the annular gear  2 . If the annular gear  2  is made to rotate, the external tooth system of the gearwheel  3  meshes with the internal tooth system of the annular gear  2  and generates a volumetric delivery flow of the fluid, in which the tooth system runs. The pair of gearwheels comprising the annular gear  2  and the gearwheel  3  is arranged in a housing  5 , with the bearing pin  4  being formed in one piece or integrally with the housing  5 . Furthermore, the annular gear  2  is connected to an annular magnet  6  in a rotationally fixed manner, with the annular magnet  6  extending around the annular gear  2  in a radially encircling manner. The annular magnet  6  runs in an inner face of a stator  7  which has an electrical winding  8 . If the electrical winding  8  is electrically commutated by a control means, a circulating magnetic field is generated in the stator  7 . On account of the circulating magnetic field, the annular magnet  6  is made to rotate, with the tooth system comprising the annular gear  2  and the gearwheel  3  also being made to operate on account of the rotationally fixed connection between the annular magnet  6  and the annular gear  2 . The annular magnet  6  is mounted on the stator  7  in a sliding manner. In this case, the annular magnet  6  is provided with a corresponding coating which is composed of a suitable sliding material. This design is not suitable for the use of high delivery pressures and with liquids which exhibit poor lubrication properties, for example gasoline or diesel. 
     The open side of the housing  5  of the internal gear pump  1  is closed by means of a connection cover  9 , with a sealing element  10  being provided in order to seal off the gap between the connection cover  9  and the housing  5  in a fluid-tight manner. The sealing element  10  is designed as an O-ring and is arranged in a corresponding encircling groove (not illustrated) inside the connection cover  9 . 
       FIG. 2  shows a section through an internal gear pump  1  according to one embodiment. The internal gear pump  1  according to the embodiment and illustrated here differs substantially from the internal gear pump  1  illustrated in  FIG. 1  in that the annular magnet  6  does not adopt the bearing function but rather the external ring or the annular gear  2  is mounted by a sliding bearing. The annular magnet  6  and the annular gear  2  are connected either in an interlocking manner or the connection is established in the embodiment by, for example, adhesive bonding of the two components to one another. A drive torque is therefore transmitted by a rotating electromagnetic field to the annular magnet  6  and further to the annular gear  2  of the internal gear pump  1 . In order to realize magnetic decoupling between the components, the gearwheel  3  is produced from non-magnetic material. In order to realize the sliding bearing on the annular gear  2 , an annular section  11  is provided, this annular section being formed in one piece or integrally with the housing  5  in this case and projecting radially from an inner wall  14  of the housing  5 . The annular section  11  is formed as a sliding bearing  25  on a first surface  15  which is opposite the annular gear  2 . There is a first radial gap  12  between a second surface  16  of the annular section  11 , which is opposite the annular magnet  6 , and the annular magnet  6 . A further second radial gap  13  is designed with low values between the annular magnet  6  and the stator  7  with the objective of achieving good torque transmission and low hydraulic friction. The width of the second radial gap  12 ,  13  is in a range of from 0.1 to 0.5 mm. 
       FIG. 3  shows a section through an internal gear pump  1  according to a further embodiment which differs from the internal gear pump  1  illustrated in  FIG. 2  in that, in this embodiment, the annular section  11  is not integrally produced with the housing  5  but rather is produced as a separate component. The annular section  11  with a bearing function is pressed or glued into the housing  5  or into a cutout  17  which is provided in the inner wall  14  of the housing  5 . 
       FIG. 4  shows a section through an internal gear pump  1  according to yet a further embodiment, with a disk-like element  18  adopting the bearing function for the annular ring  2 , said disk-like element having a bearing pin  19  which projects radially from the disk-like element  18 . The bearing pin  19  of the disk-like element  18  is arranged or mounted in a recess  20  which is formed in the bearing pin  4  of the housing  5 , with the disk-like element  18  bearing against the annular gear  2  from the outside. In this case, the sliding bearing  25  is provided between the bearing pin  19  of the disk-like element  18  and the bearing pin  4  of the housing  5 . In this case, either the surface of the bearing pin  19  or the inner wall  21  of the recess  20 , which is formed in the bearing pin  4  of the housing  5 , can be in the form of a sliding bearing. In this embodiment, fuel connections  22 ,  23  are to be provided in the housing  5 . 
       FIG. 5  shows a plan view of the internal gear pump  1  of  FIG. 4 . In this case, the position of the two fuel connections  22 ,  23 , which are produced in the housing  5 , is once again indicated by the circles which are in each case indicated using double dashed lines. 
     A structurally simple and therefore cost-effective sliding bearing is provided in the gear pump according to the invention.