Patent Document

BACKGROUND OF THE INVENTION 
     The invention relates to a pump with a rotor, having a bore for receiving a drive shaft with positive locking and which is arranged inside a pump housing, wherein the pump housing comprises a cup-shaped housing part and a further housing part which is provided with a through bore. The invention additionally relates to a pump device with a pump which comprises a rotor having a bore, and relates to a drive device with a drive shaft for driving the pump. 
     Known pumps of this type are designed, for example, in the form of vane-type pumps or gear pumps and are used for conveying gaseous or liquid substances. 
     To drive the rotor, the pump is provided with a pump shaft which is coupled by a coupling to a drive shaft, for example, a motor shaft. The pump shaft is held rotatably inside the pump housing with the aid of bearings. The bearings require space in the pump housing, and this prevents a reduction in the size of the pump housing. Furthermore, additional assembly steps are necessary for fitting the bearings. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a pump device which is small in size and which is inexpensive to produce and assemble. 
     This object is attained by a pump including a pump housing, a pump rotor in the housing, a cup-shaped housing part over the rotor and a novel connection between the rotor and a drive shaft. The further housing part of the pump is provided with a centering aid which pre-centers the drive shaft with respect to the housing part during assembly to ensure simple and reliable assembly of the drive unit and the pump so as to form a pump device. 
     The centering aid is constructed like a sleeve and is in alignment with a through bore passing through the centering aid. The internal diameter of the centering aid exceeds the external diameter of the drive shaft defining a gap between the through bore and the drive shaft. This ensures that during pumping, i.e. while the drive shaft is rotating, unnecessary friction loss does not occur between an outer wall of the drive shaft and an inner wall of the sleeve shaped insertion aid. 
     In addition, the centering aid has a longitudinal sealing portion which is adjacent to the rotor and which is provided with at least one seal. The seal is attached concentrically immediately adjacent to the rotor to ensure that the conveyed medium cannot escape in the direction of the drive unit along the drive axis and also so that undesired particles or substances cannot penetrate into the interior of the pump in the opposite direction. 
     In a preferred embodiment, the centering aid has a longitudinal centering portion which is remote from the rotor and which has axial length which exceeds the axial length of the longitudinal end portion of the drive shaft that is used for the positively locking connection. This ensures that when the drive shaft is inserted in the centering aid, the longitudinal end portion of the drive shaft which is used for the positively locking connection, can engage, pre-centered by the through bore, in the bore in the rotor and thus cannot damage or destroy the seal. This makes it possible to insert the drive shaft into the rotor of the pump without jamming and thus to assemble the pump device without errors. 
     Further, a first housing part, which is over a second housing part, comprises a centering pin which is in alignment with the longitudinal axis of the rotor and which has a smaller external diameter than the internal diameter of the bore in the rotor. The centering pin is securely mounted on the first housing part, so that the first housing part cannot jointly rotate with the rotor. In the unassembled state, i.e. without the drive shaft or without the drive unit, the rotor is held by the centering pin substantially in the center of the first pump housing, so that the drive shaft can safely engage in the rotor when inserted into the pump. Since the rotor is situated precisely centrally in the rotor housing after the assembly of the rotor, and since the external diameter of the centering pin is smaller than the internal diameter of the rotor bore, there is no unnecessary friction between the rotor and the centering pin after the drive shaft has been completely inserted in the rotor. 
     As an additional feature, the bore in the rotor has an internal set of teeth which cooperates with an external set of teeth on the drive shaft. The external set of teeth on the drive shaft is provided on the positively locking longitudinal portion of the drive shaft, as explained above. The set of teeth is used for transmitting force from a drive to the pump rotor and should thus be dimensioned such that the driving moment can be transmitted without slippage. 
     In a further preferred embodiment, the pump is a single-stroke vane-type pump. In the rest position of this pump, its rotor is arranged eccentrically to components of a pump housing forming the pump chamber. This advantageously makes it possible for force acting radially upon one side of a drive shaft of the pump, because of the single-stroke design of the pump, to center the rotor. This ensures that the rotor runs centered even if the drive shaft is bent at the operating point of the single-stroke vane-type pump. In particular, this reduces noise and wear and improves efficiency. 
     In particular, it is preferred if a longitudinal axis of a drive shaft has an offset with respect to a longitudinal axis of the pump. That offset preferably corresponds in its size and direction to the bending of the drive shaft at the operating point of the single-stroke vane-type pump. This makes it possible to compensate for the bending of the drive shaft. 
     In the pump of the invention, a drive shaft engages in the bore in the rotor with positive locking, so that the pump itself is not provided with its own pump shaft. This pump device has the advantage that by reducing the number of components required, the weight of the pump is lower than that of a conventional pump, and more compact and smaller dimensions are achieved. 
     A further advantage of the invention is afforded by dispensing with the structural groups of the mounting and the coupling which are susceptible to wear. This increases the wear resistance of the pump device, in particular for pumps supplying diesel fuel, since on account of its low viscosity, diesel fuel is unsuitable as a lubricant. 
     Other objects and features of the invention are described in an embodiment described below with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a pump device according to the invention in an unassembled state; 
     FIG. 2 is a cross-sectional view of the pump device illustrated in FIG. 1 in a partially assembled state; 
     FIG. 3 is a cross-sectional view of the pump device illustrated in FIG. 1 in the assembled state, and 
     FIG. 4 is a cross-sectional view of a variant embodiment of a pump device in an unassembled state. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The cross-sectional illustration of FIG. 1 shows a pump device  1  for supplying diesel fuel, for example, in a motor vehicle, from a storage tank to a combustion chamber of an internal-combustion engine. The pump device  1 , comprises a vane-type pump  3  and a drive device  43 , or an accessory  45  respectively, which acts as a drive motor, referred to simply as the motor  5 . These are shown in an unassembled state in FIG.  1 . This means that the vane-type pump, referred to simply as the pump  3 , and the motor  5  are not joined mechanically. The term “drive device  43 ”, is intended to cover all variants of a drive which occur in conjunction with a motor vehicle. The pump device  1  can thus be driven by the drive shaft of the internal-combustion engine, by its camshaft and also for example by a so-called drive-through shaft of an air compressor, as used for example in conjunction with the braking system of a truck. It is also possible, however, to use a separate electric motor to drive the pump device. It is assumed below that the motor  5  is used for the drive. 
     The pump  3  in turn is provided essentially with a two-part pump housing  13 , including a cup-shaped housing part  15  attached flush on the outside to a, larger shell-shaped housing part  17 , and the pump  3  further includes a rotor  7  with vanes  41  which can be displaced radially outwards as in a standard vane pump. 
     The two housing parts  15  and  17  of the pump  3  are connected together by the bolts  49 . In the sectional illustration of FIG. 1, however, only one bolt  49  is shown. In addition, for improved centering of the rotary group comprising the rotor  7  with respect to the two housing halves  15  and  17 , a plurality (two in the sectional illustration) of guide pins  69  are provided which extend at right angles to a contact face between the two housing parts  15  and  17 , and the pins  69  are inserted into the housing part  17  and into the rotary group. 
     The pump  3  is a fuel-supply pump (pre-supply pump) which has an inlet and an outlet opening  51  in order to draw the diesel fuel out of the storage tank on the one hand and to supply it to an injection pump on the other hand in accordance with the known principles of a vane-type pump  3 . A detailed description of the mounting of the vanes  41  on the rotor  7  is not provided since this is not relevant to the invention. Further, other pump principles, for example, roller-cell pumps or radial-piston pumps, can also be used. 
     Viewed centrally in the interior of the shell in the illustration, housing part  17  is provided with a centering aid  21 , which in this case is sleeve-shaped and which extends in the direction of a rotational or longitudinal axis  35  and which in this case is formed in one piece with the second housing part. A through bore  19  extends in the axial direction through the centering aid  21 . In the embodiment illustrated, the outer diameter of the centering aid  21  tapers inwards in the direction of the “shell opening”, so that on the attachment  53  of the “shell base”, the centering aid has a greater wall thickness than at the opposite end, i.e. in the “shell opening” direction. The wall thickness of the centering aid  21 , however, is of secondary importance for its operation. In the region of the attachment  53 , two axially adjacent seals  27  are fitted in a longitudinal sealing portion  25  inside the centering aid  21 . It is also possible, however, for only one or even for more seals  27  to be fitted in the center aid  21 . The further axial longitudinal portion of the centering aid  21  remote from the attachment  53  is referred to below as the longitudinal centering portion  29  and is used for pre-centering a drive shaft  11  of a drive device  43 . 
     In FIG. 1, the drive shaft  11  includes an undercutting  55  located close to its free end projecting out of the drive unit. The area between the undercutting  55  and the end face  57  of the drive shaft  11  has an external set of teeth  39  for a positively locking connection with the rotor  7 . An internal set of teeth  37  is provided in a corresponding manner on an inner wall of a central bore  9  formed in the rotor  7 , so that the internal set of teeth  37  of the rotor  7  and the external set of teeth  39  of the drive device  43  can form a positively locking connection  31 . 
     The centering aid  21  has an internal diameter d 1  which is slightly larger than an external diameter d 2  of the drive shaft  11 , producing a small gap  23  (FIG. 3) between the centering aid  21  and the drive shaft  11  in the assembled state, and preventing unnecessary friction loss during operation. 
     It is important that the length  1   l , as viewed in the axial direction, of the longitudinal centering portion  29  of the centering aid  21  be greater than an axial length l 2  which is indicated as the end of the drive shaft in FIG.  1 . That end of the shaft is comprised of the axial longitudinal portion of the external set of teeth  39  plus the axial longitudinal portion of the undercutting  55  of the drive shaft  11 . This length arrangement ensures that during the assembly of the pump device  1 , the external set of teeth  39  and the undercutting and in particular also an area adjoining the portions of the drive shaft  11  are safely guided by the longitudinal centering portion  29 . 
     The pump housing  13  additionally has a centering pin  33  oriented axially and centrally with the longitudinal axis  35 . The centering pin  33  is secured rotationally rigidly inside the first housing part  15 , preferably on an inner wall  59  of the housing, and projects in part into the bore  9  in the rotor  7 . This means that the centering pin  33  does not completely fill the space of the bore  9 , but penetrates therein only so far that the end of the drive shaft  11  can be inserted into the opposite opening of the bore for the positively locking connection  31  (FIG.  3 ). The centering pin  33  has an external diameter d 3  which is slightly smaller than an internal diameter d 4  of the rotor bore  9 . Housing part  15  is also centered with respect to housing part  17  by the centering pin  33 , since the centering pin  33  engages in the rotor of the rotor group, and the rotor group is centered with respect to housing part  17  by centering pins. 
     The cross-sectional illustration of the pump device  1  in FIG. 2 shows the pump device  1  in a partly assembled state, i.e. the pump  3  and the motor  5  are completely assembled in themselves, but the pump and the motor are not yet completely joined together. In FIG. 2 the same reference signs are used as in FIG. 1, but for clarity, the internal and external diameters d 1  to d 4  and the lengths l 1  to l 2  are not reproduced in FIG.  2 . 
     In FIG. 2, the drive shaft  11  is inserted so far into the through bore  19  in the centering aid  21  that the end face  57  of the drive shaft  11  just reaches the longitudinal sealing portion  25 . Because the axial length l 1  of the longitudinal centering portion is greater than the axial length l 2  of the external set of teeth  39 , this ensures that the drive shaft  11  is precisely centered by a guide in a region  61 , i.e. before the external set of teeth  39  reaches the seals  27 . In addition, if the drive shaft  11  is inserted further, the seals  27  and the rotor  7  are reliably prevented from being caught up or damaged. Upon further insertion of the drive shaft  11 , the centering pin  33  ensures that the rotor  7 , which is not in fact provided with its own mounting, is pre-centered such that the drive shaft  11  can be inserted into the rotor bore  9  without complications and/or damage. 
     FIG. 3 shows the pump device  1  in an assembled cross-sectional illustration, with the pump  3  and the motor  5  joined together. It is clear from FIG. 3 that the internal set of teeth  37  in the rotor and the external set of teeth  39  on the shaft  11  engage with each other in the axial center of the rotor  7  so as to produce a positively locking connection  31 . The rotor  7  is now centered so precisely by the drive shaft  11  that the centering pin  33  no longer touches the rotor  7  and the pump  3  can be driven by the motor  5 . 
     Note that the drive device  43  has a step  63  (FIG. 1) open at the edge on a motor-housing cover  65  directed towards the vane-type pump  3 . The step  63  acts as a stop for housing part  17  of the pump  3  and thus prevents the drive shaft  11  from being inserted too far into the rotor bore  9 . This ensures that a gap  47  remains between the end faces  57  of the drive shaft  11  and the centering pin  33 , so no friction loss will occur at this point. 
     The shell-shaped design of housing part  17  forms the stop, as described above, and in addition serves as a housing cover  67  for the end face of the motor  5 , so as to achieve a compact structural shape of the pump device  1 . At the same time, this can be produced inexpensively by dispensing with mounting of the drive shaft  11  inside the pump. It is clear, therefore, that the rotary group need not have its own bearing associated with it. 
     In addition, fixing the above-mentioned diameters d 1  , and d 2  ensures a gap, so as to provide easy assembly by simple centering of the parts joined together and at the same prevents loss of friction in longitudinal centering portions  29 . 
     FIG. 4 shows a further variant embodiment of a pump device, in which the same parts as in FIGS. 1 to  3  are provided with the same reference signs and are not explained again. Only the differences are explained below. 
     In the embodiment in FIG. 4, it is assumed that a single-stroke vane-type pump is involved. Such pumps have the problem that pressure builds up at the operating point of the vane-type pump in the pressure compartment, and the pressure acts radially upon one side of the drive shaft  11 . The drive shaft  11  is thus acted upon by a radial force, indicated for assistance as F in FIG.  4 . It is clear that the force F can occur only when the pump  3  is assembled and in operation. This minimally deflects the drive shaft  11 , causing the rotor  7  to be likewise slightly displaced radially, whereby the rotor is no longer situated in a centered manner with respect to the other components of the pump  3 . This increases the risk of noise generation and causes increased wear and loss of efficiency. In order to eliminate these drawbacks the following provisions are made: 
     As shown in FIG. 4 by broken lines  71 , the housing part  17  is oriented in alignment with the motor-housing cover  65 , so that the pump  3  can be joined to the motor  5  as discussed in relation to FIGS. 2 and 3. At the same time, there is an offset  73  between the longitudinal axis  35 ″ of the drive shaft  11  and a longitudinal axis  35 ′ through the pump  3 . The offset  73  produces an eccentric arrangement of the drive shaft  11  with respect to the pump  3 . 
     During the assembly of the pump device, the offset  73  makes it possible for the rotor  7 , which is mounted on the drive shaft  11  with a positive and non-positive locking connection, to be arranged eccentrically by the amount of the offset  73  with respect to the other components of the pump  3 , in particular, the housing components receiving the rotor  7 , such as the lifting ring and the side plates. To ensure that the pump device  1  is assembled despite the formation of the offset  73  between the longitudinal axes  35 ″ and  35 ′ respectively, the difference between the diameters d 1 , and d 2 , shown by gap  23  in FIG. 3, is selected so that there is sufficient play to permit assembly. At the same time, the at least one seal  27  is formed in such a way that the drive shaft  11  is received in the pump  3  in a sealed manner. 
     The offset  73  makes it possible for the rotor  7  to be arranged centrally with respect to the drive shaft  11  and eccentrically with respect to the other components of the pump  3  in the initial state of the pump device  1 . During the operation of the pump device  1 , which is constructed in the form of a single-stroke vane-type pump, the drive shaft  11  is acted upon radially in accordance with the pressure accumulating in the pressure compartment. The drive shaft  11  is acted upon radially with the force F, so that it becomes bent. The formation of the offset  73  between the longitudinal axis  35 ″ and the longitudinal axis  35 ′ is now selected such that the offset  73  corresponds in its size and direction to the bending of the drive shaft  11  at the operating point of the single-stroke vane-type pump. This compensates for the bending of the drive shaft  11 , so that at the operating point of the single-stroke vane-type pump, the rotor  7  is centered with respect to the other components of the pump  3 . Drawbacks associated with the bending of the drive shaft  11 , in particular noise generation, wear, loss of efficiency, or the like, are thus eliminated. Depending upon the structural size of the single-stroke vane-type pump (the pump  3 ) the size of the offset  73  amounts for example to between 0.05 mm and 0.2 mm. In this case the longitudinal axis  35 ′ is displaced in such a way with respect to the longitudinal axis  35 ″ that between the arrangement of the pressure compartment and the direction of the offset  73  for example an angle range of between 170° and 190°, as viewed over the periphery of the rotor  7 , is observed, i.e. they are effectively opposite. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Technology Category: 2