Abstract:
A pump-motor combination features a motor ( 30 ) and a pump ( 20 ). The pump has a first rotor ( 21 ) and a first housing  300 ). The motor is an electric motor ( 30 ) having a second rotor ( 31 ), a stator ( 33 ) and a second housing ( 32 ). The first (pump) rotor ( 21 ) is at least partially coupled, and the second (motor) rotor ( 31 ) is completely coupled, to a common rotating shaft ( 40 ), in order to enable transmission of rotation of the second (motor) rotor ( 31 ) to the first (pump) rotor ( 21 ). The structure has significant advantages when installed with the gearbox (G) or transmission of a motor vehicle, to assure supply of lubricant ( 360 ) when a primary lubricant pump ( 350 ) has not been operating, for example, upon start-up. Use of the common shaft ( 40 ) minimizes frictional losses during operation and reduces the cost of manufacture, since fewer bearings are needed, compared to the prior art.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority from German Utility Model application 20 2015 105 244.8 filed 2015 Oct. 5 by ebm-papst St. Georgen GmbH &amp; Co KG. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a pump-and-motor unit and, more particularly, to a structure in which the pump and an electric motor have a common shaft, so that the pump is driven by the electric motor in accordance with electronic control signals. 
       BACKGROUND 
       [0003]    Pump-motor units are used, particularly in the motor vehicle field, for feeding of hydraulic fluids, particularly of lubricating oil or fuel. A rotor of the pump, which conveys the fluid from the tank and compresses it, is driven by a motor, usually an electric motor. A shaft of the electric motor is connected to a rotor of the pump, in order to drive the pump. For this purpose, generally the shaft of the electric motor is rotatably journaled, by means of a bearing arrangement, in the electric motor. A pump shaft of the pump, which is securely connected to the rotor of the pump, is rotationally journaled in the pump with the help of a further bearing arrangement. To connect the shaft to the pump shaft, a coupling is provided. 
         [0004]    Thus, conventional pump-motor units have at least two bearing arrangements, as well as a coupling, leading to high development and manufacturing costs. Further, a configuration with multiple bearing arrangements means that one must reckon with elevated frictional losses, since each bearing position of the bearing arrangement creates a respective frictional loss. Higher frictional losses, in turn, necessitate an increase of the required motor capacity of the electric motor, for any given pump capacity. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is therefore to furnish a pump-and-motor unit which is cost-effective and efficiently configured. 
         [0006]    The object is achieved with a pump-motor unit wherein the pump has a first rotor and a first housing, the motor is an electric motor having a second rotor, and the first and second rotors are rotationally coupled at a common shaft, so that rotation of the electric motor rotor is transmitted, via the common shaft, to drive the rotor of the pump. Advantageous embodiments with effective and non-trivial refinements of the invention are set forth in the following description. 
         [0007]    The pump-motor unit has a motor and a pump, the pump having a first rotor and a first housing, the motor being an electric motor which has a second rotor, a stator, and a second housing. 
         [0008]    The first rotor is, at least partially, coupled for rotation with the second rotor, in order to enable transmitting a rotation of the second (motor) rotor to the first (pump) rotor. 
         [0009]    The use of a common shaft, which is at least partially connected to the first rotor, to make a connection between the first and second rotors, makes possible a cost-effective and efficient pump-motor combination. In contrast to prior art combinations, which needed two shafts, the pump-motor combination of the present invention needs only a single shaft. 
         [0010]    Reduced manufacturing cost follows directly from the reduction in component count, since providing a second shaft is no longer necessary. Further, due to using a single shaft, there is an additional cost saving because the bearing configuration is more cost-effective. Generally, each rotatable shaft needs at least two bearings. Therefore, the prior art structures with two shafts need, for reliable operation, at least four bearings. Thus, reducing the number of shafts required automatically reduces the number of bearings, so the pump-motor unit is even more cost-effective. 
         [0011]    The reduction in the bearing count leads to a reduction in friction losses since, during operation, each bearing contributes to the aggregate friction loss. This means that, with the pump-motor unit of the present invention, the same pump capacity or rating can be achieved using a smaller-capacity motor, thereby achieving an efficient pump-motor combination. Thus, the electric motor, and the complete pump-motor unit, can be made smaller and compacter, compared to those of the prior art. 
         [0012]    A further advantage is the provision of a compact pump-motor unit, since the count of bearings is reduced, and the pump-motor unit, at least in its axial dimension, can be made compactly. 
         [0013]    A further saving measure or cost reduction is the elimination of a coupling, which would otherwise be needed to connect two shafts together. 
         [0014]    A further advantage, beyond the cost-effective manufacture of the pump-motor unit, is an extension of the service life of the pump-motor unit since, due to the reduction in component count, there are fewer components which are vulnerable to failure or breakage. 
         [0015]    According to a preferred embodiment of the invention, the first rotor, which is at least partially connected to the shaft, and/or the second rotor, are coupled by press-fitting to the shaft. A force-locking coupling in the form of press-fitting or press-coupling connection between the rotors and the shaft has advantages over other types of connections. A secure connection can be created, in a simple manner, with the aid of a press-on connection. In contrast to a screw connection, no additional fastening elements are needed. 
         [0016]    Under appropriate circumstances, this connection can be undone by a corresponding application of force; during creation of the press-fit connection, releasibility by application of a predetermined amount of force can be engineered-in. Such possible releasibility is an advantage over a bonded connection, since that would form a non-releasable connection between the rotors and the shaft. 
         [0017]    According to a further embodiment, the shaft is radially journaled by using a first radial bearing and a second radial bearing, the first rotor being arranged between the first radial bearing and the second radial bearing. For radial support of the shaft, associated with the rotors, two radial bearings are provided. 
         [0018]    These two radial bearings provide a radially secured positioning of the shaft within the pump-motor unit. The advantage of the positioning of the first rotor between the two radial bearings is the achievement of a shaft which has little to no bowing, and thus a pump-motor unit with minimized wear, since such a positioning of the rotors and of the radial bearings enables a rotation-dynamically imbalance-reduced system, whose bearing loading is minimal. 
         [0019]    Due to the placement of the first rotor between the two radial bearings, the second rotor can be mounted on a side of the shaft opposite that of the first rotor, so that one of the two radial bearings is positioned between the first rotor and the second rotor. Thus a rotation system is formed having, along the shaft, a serial arrangement of a bearing-rotor pair. The first rotor, positioned between the two radial bearings, is to be arranged spaced from the two radial bearings such that its mass causes a bowing of the shaft, which can be compensated by corresponding positioning of the second rotor as a function of its mass, since one of the two radial bearings is located between the two rotors. By contrast, if both rotors were to be arranged between the two radial bearings, this would lead to severe bowing of the shaft which, due to the so-called “edge-carrying” effect adjacent the radial bearings, would subject the shaft to increased probability of failure. The same negative effect would occur with the positioning of both radial bearings between the two rotors. Thus, due to the positioning of the first rotor between the two radial bearings, a wear-minimizing pump-motor unit structure is cost-effectively achieved. 
         [0020]    To the extent that the first radial bearing and/or the second radial bearing is implemented as a slide or plain bearing, a further cost-favorable manufacture of the pump-motor unit can be achieved, since slide bearings can be made more economically than rolling bearings. 
         [0021]    According to a further embodiment, the first housing has a first housing segment and a second housing segment, wherein the first housing segment serves as the first radial bearing and the second housing segment serves as the second radial bearing. Thus, both radial bearings are implemented in the pump housing, and radial bearing support of the shaft in the electric motor becomes unnecessary. Thereby, one can create a compact pump-motor unit whose axial extent is relatively short, since one need not allocate corresponding space for arrangement of the radial bearings in the electric motor and, on a pump-remote side the electric motor, one can directly attach a control electronics module for controlling the pump-motor unit. 
         [0022]    According to a further embodiment, the first housing segment is formed as a housing cover of the pump, which advantageously simplifies assembly of the radial bearing. The first radial bearing can be formed, starting from an inner surface of the cover, particularly from a first-rotor-facing surface of the cover, as an axial extension of the first housing, and can be inserted into the cover, e.g. by press-fitting. Further, the building-in of the second radial bearing is substantially simplified, since that second radial bearing can similarly be implemented as a first-rotor-receiving inner region of the housing. 
         [0023]    According to a further embodiment, the radial bearings are formed of an aluminum-containing material. Aluminum-containing materials and aluminum alloys recommend themselves due to their relatively low weight, yet simultaneous high strength. As a function of the alloy composition, one can thus obtain high strength in the radial bearings. Especially when the radial bearings are implemented as slide or plain bearings, the bearing friction properties are favorable and, due to the high strength, the wear risk is reduced. The aluminum alloy material AlSi10Mg has proven itself to be particularly advantageous. 
         [0024]    For further component-count-reduction and thus cost-reduction in the pump-motor unit, it is advantageous if the first rotor serves for axial journaling of the shaft. Thus, in a simple manner, one can dispense with a further component, in the form of an axial bearing. 
         [0025]    Advantageously, the first housing is configured such that it limits a possible motion of the first rotor in one axial direction of the shaft, or in both axial directions of the shaft, in order to thus carry out the function of axially journaling the shaft. The first rotor is positioned, in a limiting manner, at an inner wall of the first housing. Axial displacement of the first rotor, which would tend to impair the functioning of the pump-motor unit, can be avoided by suitable configuration of the housing inner wall (preferably formed in the housing cover), so that the first rotor may abut the inner wall. Thus, the inner wall has the function of a stop. Axial displacement of the first rotor in a direction away from the housing cover can be avoided by a possible placement of the first rotor against the first housing. Thus, the first housing provides a stop which limits axial movement of the first rotor. 
         [0026]    According to a further feature of the invention, a first end of the shaft, and a second (opposing) end thereof, extend outward beyond the first housing. The advantage of having these ends projecting, with respect to the first housing, is to be seen in how an operationally-reliable assembly of the pump-motor unit is carried out. 
         [0027]    For example, in the course of making the pump-motor unit, first the first rotor of the pump is joined to the shaft by press-fitting. The shaft is then placed in the second housing segment, with both ends extending outward of the second segment. Subsequently, the housing cover is shoved over the shaft until merely enough space is left, between the first rotor and the housing cover, for rotational movement of the first rotor. Both ends of the shaft are, at the end of this assembly step, projecting beyond the first housing. Finally, the second rotor of the electric motor is secured by press-fitting to the shaft; the second rotor is thereby pushed nearly flush to the second end of the shaft. Since the press-fitting happens at a specified pressure loading, or by applying a specified force value, the first shaft end, extending beyond the first housing, is used to absorb the force, or provide a counter-force to the position-exact assembly force employed to attach the second rotor. The projection of the first end beyond the first housing permits one to avoid any damage to the connection of the shaft with the first rotor, arising from the pressing force applied during assembly with the second rotor. Thus, the need to allow, during assembly to the second rotor, the application of a predetermined pressing force to be exerted, can be compensated, without any damage to the pump resulting. 
         [0028]    According to a further feature of implementing the invention, namely a friction-minimized pairing of the radial bearing and the shaft, the shaft is composed of steel. 
         [0029]    The implementation of the pump-motor unit as a “wet-runner” has the advantage that the radial bearings (provided for journaling of the shaft) and the axial bearing can be supplied in a simple manner with lubricant, since the required lubricant can flow into and out of the pump. Thereby, a particularly long service life of the pump-motor unit is achieved. 
         [0030]    According to a further feature, the pump is implemented as a “gerotor” pump which, in comparison to other conveying pumps at the same throughput, represents a cost-effective alternative, and which permits axial forces to be particularly well taken up by the pump rotor. In gerotor pumps, the outer hollow wheel behaves like a slide bearing and, over a wide operating range, there is a positive fluid friction relationship among the components. 
         [0031]    According to a further embodiment of the pump-motor unit of the invention, at least a portion of the shaft, between the first housing and the second rotor, is free. This has the advantage that the pump-motor unit can be manufactured in a cost-saving modular structure, since a rotor packet for the electric motor can be chosen that has a length matched to that of the pump-motor unit, in which it will be used. 
         [0032]    Further advantages, features, and details of the invention will be apparent from the following description of preferred embodiments and from the drawing figures. The features, and feature combinations, described above, and the features and feature combinations disclosed in the following detailed description and accompanying drawings are usable, not just in the disclosed combination(s) but also in other combinations, or individually, without departing from the framework of the invention. Identical or identically-functioning elements are designated with identical reference numbers. For clarity of depiction, the elements may not be tagged in all the figures with their reference numbers, but their relative arrangement and functions are not lost by this. 
     
    
     
       BRIEF FIGURE DESCRIPTION 
         [0033]      FIG. 1  is a longitudinal section through the pump-motor unit of the present invention, together with the electronic controls of the motor; 
           [0034]      FIG. 2  is a perspective view of the pump-motor unit; 
           [0035]      FIG. 3  is a side view of the pump-motor unit of  FIG. 2 ; 
           [0036]      FIG. 4  is a sectional view along section line IV-IV of the pump-motor unit of  FIG. 3 ; 
           [0037]      FIG. 5  is a perspective view of a gerotor pump embodiment of the invention; and 
           [0038]      FIG. 6  is a schematic illustration of a transmission with a pump for transmission oil. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    A pump-motor unit of the present invention is constructed as shown in  FIG. 1 . The pump-motor unit  10  includes a pump  20  which, in this embodiment, is implemented as a gerotor pump. 
         [0040]    Further, the pump-motor unit  10  includes a motor  30 , which is implemented in the form of an electric motor, with a control module  50 . 
         [0041]    The pump-motor unit  10  is in the form of a secondary oil pump. 
         [0042]      FIG. 2  shows the pump-motor combination  10  in a perspective view. 
         [0043]      FIG. 3  shows the pump-motor combination  10  in a side view. 
         [0044]      FIG. 4  is a sectional view of the pump  20  (left) and of the electric motor  30  of the pump-motor combination  10  of the invention. 
         [0045]    Pump  20  has a first rotor  21  with a first rotor part  211  and a second rotor part  212  which surrounds the first rotor part  211 ; the first rotor part  211  is received therein. The rotor parts  211 ,  212  have annular shapes. An outer circumferential surface  213  of first rotor part  211  is formed with a first plurality of teeth  214  in the form of outer toothing, and an inner circumferential surface  215  of second rotor part  212  is formed with a second plurality of teeth  216 , in the form of inner toothing. During operation of the pump  20 , these teeth engage with each other. The aforementioned pump rotor  21  is arranged inside a pump stator  22  which, in the embodiment shown, is formed integrally with a first housing  200  of pump  20 , which thus serves as a pump chamber housing. 
         [0046]    The first housing  200  has a circular-cylindrical depression  201 , defining a chamber in which the first rotor  21  is rotatably mounted and is driven for rotation by the shaft  40  of electric motor  30 . 
         [0047]    Shaft  40  has a rotation axis  41 . First rotor part  211  is securely connected for rotation with shaft  40 ; a connection in the form of a press-fit is formed between first rotor part  211  and shaft  40 . Electric motor  30  is arranged opposite a facing side  202  of first housing  200 . Shaft  40  is rotatably received in a reception opening  203  defined in first housing  200 . 
         [0048]    In this embodiment, reception opening  203  is formed as a bore and extends axially along rotation axis  41 . A first rotation axis  217  of first rotor part  211  is arranged, coaxial with rotation axis  41 . 
         [0049]    Shaft  40  is shaped to extend outward of first housing  200 ; a first end  42  of shaft  40  and a second end  43  of shaft  40  project outward of first housing  200 , in such a manner that shaft  40  extends completely through chamber  201 . 
         [0050]    A second rotor  31  of electric motor  30  is, at the second end  43  of shaft  40 , connected for rotation with shaft  40 . Between the first rotor  21  and the second rotor  31 , a housing cover  204  of first housing  200  is arranged. The electric motor  30  has a second housing  32 , depicted in  FIG. 1 , which receives second rotor  31  and a stator  33  which surrounds second rotor  31 . 
         [0051]    First rotor  21  is arranged in chamber  201 ; first rotor part  211  is oriented coaxial with shaft  40  on the pump-side portion of shaft  40 . 
         [0052]    On a back side  220 , remote from front side  202 , of first housing  200  are an inlet or suction port  205  and an outlet or exhaust port  206 , as shown in  FIG. 2 . The inlet port  205  is connected via an inlet chamber  209 , formed as a part-circular recess in first housing  200 , with an inlet region  210  of chamber  201 , while analogously the outlet port  206  is connected via an exhaust chamber  207 , formed as a part-circular recess in first housing  200 , to an exhaust or expelling region  210  of chamber  201 . The inlet chamber  209  is preferably arranged diametrically opposite the exhaust chamber  208 . 
         [0053]    However, a differing arrangement is also possible, for example, an angular spacing of about 150° between the chambers, the spacing being measured between the centers of the chambers. 
         [0054]    Second rotor part  212 , which surrounds first rotor part  211 , and thus is configured as an external rotor, is rotatably mounted in cylindrical chamber  201 , essentially coaxial with chamber  201 . 
         [0055]    A longitudinal axis  221  of chamber  201  corresponds to second rotation axis  218 , and is parallel to the first rotation axis  217  corresponding to rotation axis  41 . It is further to be noted that the inner toothing of second rotor part  212  has more teeth than the outer toothing of the first rotor part  211  which is arranged eccentrically with respect to the second rotor part  212 . 
         [0056]    A rotation of first rotor part  211  leads, due to the engagement between the teeth of first rotor part  211  and of second rotor part  212 , to co-rotation of second rotor part  212 . The partially-engaging teeth of the first plurality of teeth  214  and of the second plurality of teeth  216  are completely engaged with each other only in a particular angular range. In an exactly opposing angular range, the first plurality of teeth  214  and the second plurality of teeth  216  are spaced from each other and are not engaged with each other. 
         [0057]    The rotation of first rotor  21  leads to a so-called “overtaking” in the rotation direction of the second plurality of teeth  216  by the first plurality of teeth  214 . During rotation, there arises, between two adjacent respective opposing teeth of the first rotor part  211  and of the second rotor part  212 , a interstitial space or volume  219 , having a regularly alternating size. As soon as, due to the rotation, the engagement between the respective opposing teeth of first rotor part  211  and second rotor part  212  is released, interstitial space  219  reaches a maximal size. Upon further rotation, the size of interstitial space  219  declines, starting with a partial engagement of the teeth of first rotor part  211  and second rotor part  212 , and leading to full engagement between these teeth. As soon as the full engagement is formed, the interstitial space  291  ceases. 
         [0058]    During the rotation phase of the growth of interstitial space  219 , this space moves past the inlet port  209  so that, via the suction channel  205 , hydraulic medium is sucked into interstitial space  209 . During the rotation phase of the declining volume of interstitial space  219 , this space moves past the exhaust port  207 , so that hydraulic medium is fed, via the exhaust port  207 , to outlet connection  205  with elevated pressure. 
         [0059]    In accordance with the invention, the first rotor part  211  and the second rotor  31  are secured for rotation with the common shaft  40 , in order to enable transmission of rotation of the second rotor  31  to the first rotor  21 . Second rotor  31  is preferably connected by press-fitting to shaft  40 , so that they rotate together. 
         [0060]    Shaft  40  is radially supported in housing  200  by means of a slide bearing. There is a first radial bearing  222  in housing cover  204  of housing  200 , and a second radial bearing  223  in a second segment  225  (at back side  220 ) of housing  200 . Thus, first rotor  21  is arranged between first radial bearing  222  and second radial bearing  223 . Alternatively, radial bearings  222 ,  223  could be implemented as ball bearings. 
         [0061]    Axial bearing support, which limits an axial motion of shaft  40  along the rotation axis  41 , is carried out with the help of first rotor  21 , which is axially limited in a first housing segment  224  which, in this embodiment, is implemented as housing cover  204 . Thus, first housing  200  serves for axial support and mounting of shaft  40 . 
         [0062]    In order to reduce friction losses, the axial bearings  222 ,  223  are composed of an aluminum-containing material, preferably the alloy AlSi10Mg. The formation of shaft  40  of steel results in a favorable, particularly low-friction pairing of the components  224 ,  225 ,  40  which are in contact with each other. 
         [0063]    The pump-motor unit  10  is implemented as a so-called “wet runner” or “wet-dial” unit and is arranged in an oil pan ( FIG. 6 ) of a transmission or gearbox (not shown in detail). It serves as an additional oil pump, or as a secondary oil pump, for the transmission, to the extent that a main oil pump ( FIG. 6 ) is inactive. Via the inlet connection  205 , during operation of the secondary oil pump, oil is sucked from the oil pan, compressed in the pump  20 , and fed via the pressure outlet  206  to the transmission, which is connected, directly or indirectly, via an oil conduit with the pressure outlet  206 . 
         [0064]    A control electronics unit  51  of the control apparatus  50  is connected on a pump-remote side of the pump-motor unit  10 . 
         [0065]    The control apparatus has a third housing  60 . 
         [0066]    The implementation as a “wet-runner” facilitates lubrication oil supply to the bearings  222 ,  223 . A through-passage opening  226  (formed starting at receiving opening  203 , which extends completely through first housing  200 ), enables in- and out-flow of the lubrication oil in pump  20 ; thereby, the bearings  222 ,  223  and the first rotor part  211  provided for axial support, can be provided with lubricant. Similarly, lubricant entering via opening  226  passes via the pump into the electric motor  30  and exits at a motor cover formed at a pump-remote end of electric motor  30 , and vice versa. Preferably, the suction regions  209 ,  210  on the front side of the pump rotors  211   212  and the receiving opening  203  are in fluid communication via a fluid channel  227 , in order to make possible, via suction regions  209 ,  210 , a supply of oil to the receiving opening  203 , and to thereby assure a better lubrication of shaft  40 . 
         [0067]      FIG. 5  illustrates schematically the structure of a gerotor pump  300 . The pump rotor has an inner toothed wheel  302  and an outer toothed ring  303 , whose inward-pointing teeth mesh with the outward-pointing teeth of inner wheel  302 . Inner wheel  302  and outer ring  303  are eccentrically mounted with respect to each other, and have differing respective numbers of teeth. Therefore, inner wheel  302  and outer ring  303  turn at different respective rotation speeds, so that, during rotation, the size of the voids or interstitial spaces between the respective teeth fluctuate between a maximum volume and a minimum volume. 
         [0068]    Pump  300  has a fluid inlet  304  and a fluid outlet  305 . Fluid inlet  304  is in fluid communication (via a channel, not shown) with the facing sides of inner wheel  302  and of outer ring  303  at a region where, for a predetermined rotation direction, the void size decreases, thereby creating excess pressure, which expels the fluid to be conveyed. 
         [0069]      FIG. 6  shows a possible schematic structure of a transmission apparatus  370  with a schematically indicated housing  372  in which, at the bottom, transmission oil  360  is provided. The actual mechanical transmission gears  354  must, in operation, be lubricated by the transmission oil  360 . For this purpose, a first transmission oil main pump  350  is provided, which is mechanically driven, from transmission  354 , via a mechanism  352 , in order to supply transmission oil  360  via a conduit  358  to the transmission  354 . However, transmission oil main pump  350  only functions when transmission  354  is moving. In a stationary state of transmission  354 , transmission oil main pump  350  is not active, and lubrication of transmission  354  is not assured, especially upon start-up of transmission  354 . Therefore, the supplemental or auxiliary oil pump  310 , driven by electric motor  30 , is provided. It can, as needed, pump oil  360  via conduit  356  and non-return valve  357  into conduit  358 , and thence into transmission  354 . The non-return value  357  is provided to prevent flow of transmission oil from main pump  350  into supplemental pump  310 . The transmission oil  360  applied to transmission  354  subsequently flows back down into the oilpan, and can be later pump back up again. Alternatively, pump  310  could naturally be installed as the main transmission oil pump  350 . 
         [0070]    Those having ordinary skill in the fluid pumping art will understand that many variations and modifications are possible, within the scope of the inventive concept. Therefore, the invention is not limited to the specific embodiments described above, but rather is defined by the following claims.