Abstract:
The invention relates to a centrifugal pump ( 100 ), in particular for a coolant in a motor vehicle, comprising a first centrifugal pump stage ( 102 ) having a first pump housing ( 108 ), and a first impeller ( 110 ) rotatably mounted therein, and to a drive device ( 106 ) for coaxially driving the first impeller. A second centrifugal pump stage ( 104 ) has a second pump housing ( 114 ) and a second impeller ( 116 ) rotatably mounted therein and an intermediate housing ( 120 ) is located between the first and the second pump housing ( 108, 114 ) for diverting a fluid flow dispersed by the first impeller to an inlet region of the second impeller.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a centrifugal pump. In particular, the invention relates to a two-stage centrifugal pump for a coolant in a motor vehicle. 
         [0002]    Single-stage centrifugal pumps, for example for conveying a coolant, are known in various variations. For example, EP 1850448 A1 shows a single-stage centrifugal pump in which a rotor of an electric motor driving the centrifugal pump is designed to be integrated with an impeller of the centrifugal pump. 
         [0003]    In complex environments such as in a motor vehicle, varying requirements are placed on a centrifugal pump. For example, modern motor vehicles comprise diverse additional cooling circuits, for example for intake air cooling or for cooling electronic modules, which can require a higher build-up of pressure with the same or lower delivery volume as compared with a centrifugal pump used in a main cooling circuit. A single-stage centrifugal pump in principle suitable for these requirements, with a higher capacity than the main centrifugal pump, is usually substantially more expensive and has a larger external diameter, so that it cannot as readily be fitted in the motor vehicle as the main centrifugal pump. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore an object of the invention to specify a centrifugal pump which, with the same build-up of pressure, has compact external dimensions and is simple to assemble. 
         [0005]    According to a first aspect of the invention, a centrifugal pump, in particular for a coolant in a motor vehicle, comprises a first centrifugal pump stage having a first pump housing and a first impeller rotatably arranged therein, a drive device for the coaxial drive of the first impeller, a second centrifugal pump stage having a second pump housing and a second impeller rotatably arranged therein, and an intermediate housing arranged between the first and the second pump housing for deflecting a liquid stream discharged from the first impeller to an inlet region of the second impeller. 
         [0006]    By using a two-stage centrifugal pump, the liquid to be conveyed can firstly be conveyed in the first centrifugal pump stage and then placed under increased pressure in the second centrifugal pump stage. In this way, an increased pressure elevation with respect to a single-stage centrifugal pump can be implemented with a constant external diameter, so that an existing installation space can be used unchanged and, if necessary, fixing elements such as a rubber sleeve can be incorporated unchanged. The intermediate housing can comprise deflection elements which deflect the liquid stream from an outflow region of the first impeller that is remote from the axis to an inlet region of the second impeller that is close to the axis. The deflection elements can, for example, run in a sickle shape toward a common axis of rotation of both impellers. 
         [0007]    The intermediate housing can be connected integrally to the second pump housing. Integrity permits a corrosion-resistant and therefore rugged and long-lasting connection. The connection can be made, for example, by means of adhesive bonding, laser welding, ultrasonic welding, hot stamping or another known type of connection. In a further embodiment, the intermediate housing can also be connected to the first pump housing. Furthermore, the intermediate housing can also be connected to one of the two pump housings in an only force-fitting manner by means of any desired known technique. The connection produces a unit that can be handled separately, which may be advantageous when assembling the centrifugal pump. 
         [0008]    The pump housings of the centrifugal pump can adjoin each other, and the intermediate housing can be accommodated in the first pump housing. The intermediate housing can occupy a space in the first pump housing which is provided in a similar way in the second pump housing and is filled there, for example, by a section of the adjacent drive device. Thus, the two pump housings can have internal geometries which are similar or identical in some sections, which can reduce fabrication costs. 
         [0009]    The drive device can comprise a bearing pin and a rotor with a drive sleeve rotatably mounted on the bearing pin, to which the second impeller is connected in a torque-transmitting manner. The bearing pin can be arranged to be rotationally fixed with respect to a stator of the drive device. In this way, the second impeller does not have to be produced in a manner integrated with the rotor but can be connected to the rotor in a torque-transmitting manner only within the context of pre-assembly or final assembly. Furthermore, the first impeller can also be rotatably arranged on the bearing pin, so that axial alignment of the drive device and both impellers is ensured by means of the bearing pin. 
         [0010]    The first impeller can be connected to the drive sleeve in a torque-transmitting manner by means of a driver geometry. The driver geometry can, for example, comprise interengaging crown-like contours on adjacent end faces of the drive sleeve and of the first impeller. The driver geometry can be formed in such a way that the first impeller can be brought into engagement with the drive sleeve without expenditure of force, so that an assembly operation has no influence on the precision of the arrangement. 
         [0011]    The first impeller can also be connected to the second impeller in a torque-transmitting manner by means of a driver geometry. 
         [0012]    The first centrifugal pump stage, the second centrifugal pump stage and the drive device can be arranged axially one after another, and the first pump housing can comprise an intake spigot leading to an inlet region of the first impeller that is close to the axis. As a result, in particular a section of the two-stage centrifugal pump that faces away from the drive unit can be formed as in the single-stage centrifugal pump, so that interchangeability is made easier. 
         [0013]    A gap region between the rotating first impeller and the first pump housing can correspond to a gap region between the rotating second impeller and the second pump housing, so that the second impeller can be inserted into the first pump housing instead of the first impeller, in order to form a single-stage centrifugal pump. During fabrication of centrifugal pumps on a partly or fully automated production line, it is thus possible to change between the production of single-stage centrifugal pumps and two-stage centrifugal pumps with manageable conversion expenditure. 
         [0014]    According to a second aspect of the invention, a method for assembling the above-described two-stage centrifugal pump comprises steps of pushing the second impeller onto the drive sleeve of the rotor, placing the second pump housing with the intermediate housing on the drive device, pushing the first impeller onto the bearing pin and placing the first pump housing on the second pump housing. 
         [0015]    As a result of the chosen structure of the centrifugal pump, its final assembly comprises only a few operations that can be carried out with low requirements, for example on precision, expenditure of force and speed. 
         [0016]    The method can also comprise the prior step of connecting the intermediate housing to the second pump housing. In this way, a unit that can be handled separately is produced, which further simplifies the assembly method. Optionally, the second impeller can also already previously be joined to the drive sleeve and the rotor of the drive device to form a unit that can be handled separately. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will now be described with reference to the appended drawings, in which: 
           [0018]      FIG. 1  shows a longitudinal section through a two-stage centrifugal pump; 
           [0019]      FIG. 2  shows an isometric view of the second pump housing with the intermediate housing from  FIG. 1 ; 
           [0020]      FIG. 3   a  shows a torque-transmitting connection of the first impeller to the second impeller in  FIG. 1 ; 
           [0021]      FIG. 3   b  shows a variation of the connection from  FIG. 3   a ; and 
           [0022]      FIG. 4  shows a method for assembling the centrifugal pump from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Identical or mutually corresponding elements bear the same designations in all the figures. 
         [0024]      FIG. 1  shows a longitudinal section through the centrifugal pump  100 . The centrifugal pump  100  comprises a first pump stage  102 , a second pump stage  104  and an electric motor  106  as drive device. The first pump stage  102  comprises a first pump housing  108  and a first impeller  110 , between which a first gap region  112  is formed. The second pump stage  104  comprises a second pump housing  140  and a second impeller  116 , between which a second gap region  118  is formed. In a region between the first pump stage  102  and the second pump stage  104  there is arranged an intermediate housing  120 . The first pump housing  108  rests on the second pump housing  114  and is sealed off with respect to the latter by means of an O-ring  122 . The second pump housing  114  rests on the electric motor  106  and is sealed off with respect to the latter in a corresponding way by means of an O-ring  124 . 
         [0025]    The electric motor  106  comprises a stator  128 , a rotor  130  having permanent magnets  132 , also a drive sleeve  134 , a bearing pin  136 , an electric control device  138  and a housing  140 . Bolt channels  142  run through the first pump housing  108 , the second pump housing  114  and the housing  140  of the electric motor  106 , in order in each case to accommodate bolts (not illustrated) which hold the centrifugal pump  100  together. 
         [0026]    A flow direction of a liquid through the centrifugal pump  100  is indicated by means of arrows. The liquid enters at the bottom through an intake spigot  144  formed on the first pump housing  108  and then reaches an inlet region of the first impeller  110  that is close to the axis. The impeller  110  rotates about the bearing pin  136  during operation, so that the liquid is accelerated in the radial direction and is discharged outward. On its left-hand side, the intermediate housing  120  has a cut-out, through which the liquid discharged rises and flows along deflection elements  146  of the intermediate housing  120  toward the bearing pin  136 . From there, the liquid passes further upward into an inlet region of the second impeller  116  that is close to the axis. During operation, said impeller  116  likewise rotates about the bearing pin  136 , so that the liquid is again accelerated in the radial direction and is discharged outward. The second pump housing  114  has a larger internal diameter than the external diameter of the second impeller  116 , so that a radial interspace is formed, along which the liquid discharged flows in the direction of a pressure spigot  148  which is formed on the circumference of the second pump housing  114  and through which the liquid finally leaves the centrifugal pump  100 . 
         [0027]    At its upper end, the bearing pin  136  is rotationally fixedly accommodated in a section of the stator  128 , for example by means of a press or fit connection. Rotatably arranged on the bearing pin  136  is the drive sleeve  134 , which is connected in a rotationally stable manner to the permanent magnets  132  and the second impeller  116 . In order to fix the permanent magnets  132  to the drive sleeve  134 , further components can be used, for example a magnet carrier (not shown). The latter can enclose the permanent magnets  132  in a liquid-tight manner. Apart from this, the liquid to be conveyed flows freely around the rotor  130 . A position of the drive sleeve  134  on the bearing pin  136  at the top is bounded by the drive sleeve  134  resting on the stator  128 . 
         [0028]    At its lower end, the bearing pin  136  is arranged in a receptacle formed on the first pump housing  108 . The bearing pin  136  is chamfered at its lower end in order to facilitate its insertion into the receptacle. Above the receptacle, the first impeller  110  is arranged such that it can rotate about the bearing pin  136 . For this purpose, between the first impeller  110  and the bearing pin  136  there is arranged a bearing bush  150 , which is connected in a rotationally stable manner to the first impeller  110 , for example by means of shrinking, pressing, adhesive bonding or injection molding on. A position of the first impeller  110  on the bearing pin  136  at the bottom is bounded by the first impeller  110  resting on the first pump housing  108 . A device for transmitting torque from the second impeller  116  or the drive sleeve  134  to the first impeller  110 , which also delimits the position of the first impeller  110  at the top and of the drive sleeve  134  at the bottom, is not illustrated in  FIG. 1  and will be described extensively below with reference to  FIGS. 3   a  and  3   b.    
         [0029]      FIG. 2  shows an isometric illustration of the intermediate housing  120 . In the middle, the intermediate housing  120  has a round central cut-out  205 ; in the front region a lateral cut-out  210  can be seen, through which the liquid can flow from the underside of the intermediate housing  120  to the deflection elements  146  in the region of the upper side of the intermediate housing  120 . Arranged on an upper surface of the intermediate housing  120  are five sickle-like deflection elements  146 , which run from a radius of the intermediate housing  120  to the central cut-out  205 . The radius is chosen such that liquid can flow unimpeded around a radially outer region of the upper side of the intermediate housing  120 . 
         [0030]    Each deflection element  146  has a pin  220  on its upper side to engage in and optionally to be adhesively bonded to corresponding cut-outs in the second pump housing  114 . In another embodiment, the pins  220  are missing and the intermediate housing  120  is adhesively bonded flat to the second pump housing  114  in the region of the deflection elements  146 . Connecting the intermediate housing  120  to the second pump housing  114  produces a unit that can be handled separately. 
         [0031]      FIG. 3   a  shows a device, not illustrated in  FIG. 1 , for transmitting torque between the first impeller  110  and the second impeller  116 . The first impeller  110  is rotationally fixedly connected to the bearing bush  150 , which is freely rotatably mounted on the bearing pin  136 . As distinct from the illustration in  FIG. 1 , the bearing bush  150  runs through the first impeller only in a lower section. 
         [0032]    The second impeller  116  is rotationally fixedly connected to the drive sleeve  134 , which is freely rotatably mounted on the bearing pin  136 . In the region of the bearing pin  136 , the lower end of the second impeller is shaped so as to point sufficiently far downward that its lower end face adjoins the upper end face of the first impeller  110 . As a result, a distance between the impellers  110  and  116  on the bearing pin  136  is restricted. In the region of the abutting end faces of the impellers  110  and  116  there is a crown profile  152 , of which one peak can be seen on the right-hand side of the bearing pin  136 . With the aid of the crown profile  152 , the impellers  110  and  116  are connected to each other in a torque-stable manner. The interengaging flanks of the crown profile  152  can run around the bearing pin  136  in the form of a rectangle, trapezium or corrugation, and it is possible for one or more peaks to be enclosed by the crown profile  152 . Adjacent flanks of the peaks can run in parallel or else at an angle to one another, so that a torque is preferably transmitted in a direction of rotation. As a result, assembly of the impellers  110  and  116  on each other can be made easier. In a further embodiment, it is also possible for a driver pin (not illustrated) parallel to the bearing pin  136  to engage in corresponding cut-outs in the impellers  110  and  116  and connect the latter to each other in a torque-transmitting manner. 
         [0033]      FIG. 3   b  shows an alternative embodiment of the device shown in  FIG. 3   a  for use in the centrifugal pump  100  from  FIG. 1 . The device corresponds substantially to that from  FIG. 3   a , with the difference that it is not the lower end face of the second impeller  116  but the lower end face of the drive sleeve  134  that engages with the upper end face of the first impeller  110  via the crown profile  152 . 
         [0034]      FIG. 4  shows a method  400  comprising steps  405  to  465  for the assembly of the centrifugal pump  100  from  FIG. 1 . In step  405 , the method  400  is at the start. In the first step  410 , the stator  128 , together with the housing  140  and the control device  138 , is oriented such that the bearing pin  136  points upward. Then, in step  415 , the rotor  130  with the permanent magnets  132  is pushed onto the drive sleeve  134 . After that, in step  420 , the second impeller  116  is pushed onto the drive sleeve  134 . The subassembly created in this way is pushed onto the bearing pin  136  in the following step  425  and lies on the stator  128  of the electric motor  106 . After that, the second O-ring  124  is inserted into the second pump housing  114  and then, in step  435 , the second pump housing  114  is placed on the electric motor  106 . 
         [0035]    Then, in step  440 , the first impeller  110  is pushed onto the bearing pin  136 . Then, in step  445 , the first O-ring  122  is inserted into the first pump housing  108  and the first pump housing  108  is placed on the second pump housing  114  in step  450 . 
         [0036]    In the following steps  455  and  460 , bolts are introduced into the bolt channels  142  and tightened, for example by screwing or riveting. After that, the method is at the end  465 . 
         [0037]    By means of the method  400 , the centrifugal pump  100  can be assembled efficiently, higher forces having to be applied only in the steps  415  and  420 , which can also be carried out separately, and in the final step  460 . In intermediate stages between the method steps  405  to  465  of the method  400 , elements of the pump  100  that have already been arranged on one another are held on one another by gravity, so that no holding or clamping devices are required. As a result of using a crown profile  152 , the mounting of the movable components  110 ,  150 ,  116 ,  134  of the centrifugal pump  100  along the bearing pin  136  is defined and, at the same time, a torque flow to the first impeller  110  is produced without loading elements of the centrifugal pump  100  mechanically by the assembly operation.