Abstract:
An electrically operated crescent pump of a hybrid drive train conducts entrapped oil emerging from the oil pump to windings of the stator in order to cool the electric motor of the pump.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an oil pump which can be driven by an electric motor and supplies working pressure to a gearbox.  
         [0003]     2. The Prior Art  
         [0004]     German Patent No. 101 60 466 C1 describes an oil pump which can be driven by an electric motor. This oil pump is applied in a drive train of a hybrid vehicle.  
         [0005]     In addition, PCT/EP03/11979 (not published before the priority date of this application) describes a drive train of a hybrid vehicle. This drive train also has an oil pump for the gearbox.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore an object of the invention to provide a particularly operationally reliable pump which can be driven electrically.  
         [0007]     This object is achieved according to the invention by an oil pump for supplying a gearbox having a housing with working pressure, comprising an electric motor connected to the pump for driving the pump, and a sealing gap in the pump through which an oil stream is fed to a winding of the electric motor for cooling purposes.  
         [0008]     Such a particularly failsafe oil pump can be applied in particular in a drive train of a hybrid vehicle, since in such a vehicle, particularly stringent requirements are made of failsafety. As a result, if a mechanically driven pump is eliminated, the electrically operated oil pump must nevertheless provide 100% availability. This oil pump must also ensure the necessary operating pressure very quickly. As a result, the electric motor cannot itself be embodied as a high-inertia electric motor of the electric locomotive drive. Rather, the electric motor of the oil pump must be embodied as a separate highly dynamic electric motor. However, even if the electric oil pump is used in addition to a mechanical oil pump which is operated directly by the internal combustion engine, 100% availability for the operating ranges in which a purely electric drive of the hybrid vehicle takes place when the internal combustion engine is switched off is necessary.  
         [0009]     One advantage of the invention is that a separate cooling system is provided for the oil pump, with the oil pump itself supplying oil to the actual electric motor which drives it. Entrapped oil which emerges from the oil pump is diverted to its electric motor for cooling purposes.  
         [0010]     As a result of the self-cooling, the risk of failures which are associated with thermal overloading of the electric motor are reliably ruled out. In particular, the insulation layers of the windings are reliably cooled.  
         [0011]     The oil pump is preferably arranged within the gearbox housing in the gearbox oil/air space of the gearbox so that a favorable “packaging” is obtained, i.e. the hybrid drive with an oil pump can be accommodated, with only a slightly enlarged overall installation space in the same installation space in which otherwise identical drive trains with a purely internal combustion engine drive are accommodated. As a result, the same bodywork structure can be used for hybrid vehicles and standard vehicles.  
         [0012]     In particular, when a hydrodynamic torque converter—as a starting element of the gearbox—is replaced with an electric motor for the hybrid drive, the electrically operated oil pump can even be installed with corresponding overall installation space conditions of the locomotive drive electric motors even without enlarging the overall space in comparison with the standard drive.  
         [0013]     When the oil pump according to the invention is arranged inside the gearbox housing in the gearbox oil/air space of the gearbox, there is a larger room for maneuver in the design of the gearbox housing, since the latter does not need to conduct away the heat of the electric motor of the oil pump since the heat can be transported to any desired location via the gearbox oil for the purposes of cooling. As a result, approximately 200 Watt thermal power can be carried away from a high-torque vehicle. In this case, the oil balance of the gearbox is not affected by the additional volume flow rate required for the additional cooling of the electric motor of the oil pump. In this arrangement in the gearbox oil/air space, the electric motor of the oil pump is advantageously configured so as to be insensitive to the gearbox oil.  
         [0014]     As shown in the drawing, the oil pump distributes the oil uniformly to the stator which is fixed to the housing. At the same time, the oil is diverted in a particularly advantageous way into an annular gap by utilizing gravity and a centrifugal effect, which gap is formed between the rotor of the electric motor and a gearbox housing wall. Roller bearings of the rotor are also cooled/lubricated in a particularly advantageous way by the oil in the annular gap. The oil is prevented from flowing away freely by a retaining edge. The oil which is partially accumulated is forced from the annular gap into a rotor bore. This rotor bore can end in particular between two magnets underneath the banding of the rotor. This banding may particularly advantageously be a tubular component, which in addition to the function of conducting oil, has the function of absorbing the centrifugal forces of the magnets. If the oil stream through the rotor bore impinges on the banding, the oil stream can be particularly advantageously diverted to two axial annular outlets of the rotor.  
         [0015]     In one particularly advantageous refinement of the invention, the banding can have cutouts in the region of the rotor bore which may be embodied as bores or punched-out elements. In this refinement, an air gap between the rotor and stator of the electric motor can be filled with oil, which promotes the cooling of the stator and, under certain circumstances, is also beneficial for the power of the machine.  
         [0016]     Irrespective of the way in which the banding is embodied, the oil stream emerges, or both oil streams emerge, underneath the windings of the stator so that these warmest surfaces of the stator are advantageously sprayed first with cool oil.  
         [0017]     If the outlet openings for the oil are formed circumferentially in the rotor, the oil stream is distributed particularly advantageously uniformly over the windings against the force of gravity. The heated oil can be particularly advantageously removed by being drawn downwards by the force of gravity. In particular the oil can escape through outflow bores.  
         [0018]     In addition to the cooling of the oil by means of oil which is thrown outwards by the rotor, a further cooling oil stream, which is directed from the top to the bottom over the windings, may be provided in order to cool the external windings.  
         [0019]     The oil pump is preferably embodied as a gearwheel pump. In particular, a crescent pump can be used as the oil pump in such a case.  
         [0020]     The gearbox can also be in particular an infinitely variable automatic transmission such as, for example, a toroidal gear mechanism. Using the failsafe oil pump of the invention is advantageous in particular in such an infinitely variable automatic transmission since in such a transmission the traction means is destroyed within a very short time if the specific gearbox oil “traction fluid” is not present between the 
        roller and/or     belt and/or     chain 
 
 and 
    the toroidal surface and/or     bevel gear.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.  
         [0027]     The drawing shows a cross-sectional view of a drive train of a hybrid vehicle, having an oil pump according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     In the drawing,  FIG. 1  shows a detail from a drive train of a hybrid vehicle. Such a drive train comprises an electric machine which is arranged between an internal combustion engine (not illustrated in more detail) and a gearbox of a motor vehicle. The motor vehicle may be driven either by the internal combustion engine or alternatively by the electric machine. The motor vehicle can also be operated in a “boost operating mode”, either with the internal combustion engine or the electric machine, in order to increase the driving-off/acceleration power. Such a drive train is described in PCT/EP03/11979, whose content is hereby incorporated by reference.  
         [0029]     The internal combustion engine and the gearbox are arranged coaxially with respect to a central axis  13 . This central axis  13  is used below as a reference axis for the expression “axial”. A pressure-regulated oil pump is located inside a gearbox housing of the gearbox. This oil pump is embodied as a crescent pump  14 . A working pressure is built up in a gearbox oil by means of pump  14 , which pressure is supplied to the actuating elements of the automatic transmission via a duct  15  so that laminated clutches/brakes can be engaged/disengaged in order to couple planetary gear sets or a gearbox housing. The working pressure which is produced by the crescent pump  14  is between 5 and 25 bar.  
         [0030]     Crescent pump  14  is composed here of an internally toothed outer gearwheel  16 , a crescent  17  and an externally toothed inner gearwheel  12  which is driven by a central sleeve  19  which is connected fixed in terms of rotation to gearwheel  12 . Crescent pump  14  has sealing gaps here through which pressurized gearbox oil escapes as entrapped oil, as it were as leakage, from a pump housing of crescent pump  14 . This pump housing is formed by the gearbox housing walls  11 , shown only partially in the drawing, of the gearbox housing. The entrapped oil emerges axially on both sides of crescent pump  14 , i.e., the entrapped oil emerges at the sealing gap  20  (shown in  FIG. 1 ) between the gearbox housing wall  11  and the inner gearwheel  12 . In this case, crescent pump  14  is configured so that more entrapped oil emerges at sealing gap  20  than at the sealing gap which is not shown in the drawing, on the other side of the crescent pump  14 , i.e., axially at the rear.  
         [0031]     In order to form a rotationally fixed connection between the inner gearwheel  12 , gearwheel  12  has radially inwardly directly teeth which engage in slits in sleeve  19 . Sleeve  19  is caulked in a fixed fashion at its axially front end—i.e. the end facing away from the crescent pump  14 —to a radially inwardly projecting annular web  21  of a rotor  3  of the electric motor. The annular web  21  is located at the axially front end of rotor  3  so that an annular projection  22  of gearbox housing wall  11  extends axially to the left into the intermediate space between rotor  3  and sleeve  19  to just before radial annular web  21 . The annular gap which is thus formed between projection  22  and components  19 ,  21  of rotor  3  has an approximately continuous gap size up to a retaining edge  4 . This retaining edge  4  forms a throttle point which extends radially inwards in the direction of shoulder  22  at the axially rear end of rotor  3  so that the aforesaid throttle point is formed at the very narrow annular gap which is thus produced. An axial needle bearing  23  and a radial needle bearing  40  are arranged in the annular gap. The axial needle bearing  23  supports annular web  21  axially against an end edge of projection  22 , while the radial needle bearing  40  supports sleeve  19  in the radially outer direction against an inner side of projection  22 . At the axially front side, annular web  21  is supported axially by means of a further axial needle bearing  24 .  
         [0032]     Axially in the center, rotor  3  has a plurality of rotor bores  5  which are distributed uniformly around the circumference and which extend radially outwards through rotor  3 , irradiating from central axis  13 . Tubular banding  7  is fitted coaxially onto rotor  3 . This banding  7  absorbs the centrifugal forces of permanent magnets  6  which are inserted into rotor  3 , distributed uniformly around the circumference. The aforesaid rotor bores  5  each end here between two permanent magnets  6  which are arranged spaced apart from one another along the circumference so that a duct  25  is formed which extends axially to the front and rear from the respective rotor bore  5 . Stator  2  of the electric motor is arranged distributed uniformly along the circumference in the radial direction outside rotor  3 . By correspondingly energizing windings  26  of stator  2 , rotor  3  can be made to rotate so that internal gearwheel  12  which is coupled fixed in terms of rotation to rotor  3  rotates and crescent pump  14  builds up the working pressure between 5 and 25 bar in the gearbox oil.  
         [0033]     Stator  20  is pressed into a gearbox housing part  28  so as to be fixed in terms of rotation. Connecting lines  27  are also led into this gearbox housing part  28 .  
         [0034]     Winding  26  of stator  2  is secured axially at the front by means of a plate to a circlip DIN  472  which is inserted into an internal annular groove of gearbox housing part  28 . This gearbox housing part  28  ends axially in front of circlip DIN  472 . An additional oil stream  30  for cooling the electric motor is conducted along at upper front end  29  in front of this gearbox housing part  28 . Due to the force of gravity, this additional oil stream  30  runs along stator  2  to the lower end and is for the most part conducted away again from there at axial front end  29 .  
         [0035]     Winding  26  bears radially on the outside of gearbox housing part  28 . Axially behind winding  26 , a breakthrough  10  extends radially upwards through gearbox housing part  28 . An additional oil stream  31  for cooling the electric motor is also introduced through this upper breakthrough  10 . Due to the force of gravity, this additional oil stream  31  flows to the lower end and is for the most part conducted away from there via outflow bores  32 . Because of the arrangement of the breakthrough  10  at the upper side, oil stream  31  divides and flows along the circumference on both sides of stator  3 .  
         [0036]     An oil stream  1  of the aforesaid entrapped oil flows along sealing gap  20  due to the internal pressure of crescent pump  14 . Since rotor  3  rotates, due to the centrifugal force which acts on it, oil stream  1  subsequently flows through the aforesaid annular gap which is formed between projection  22  and components  19 ,  21  of rotor  3 , as far as retaining edge  4 . There, oil stream  1  is throttled so that the greater part of oil stream  1  flows through rotor bores  5  and duct  25  and is subsequently thrown radially outwards onto stator  2 . There, oil stream  1  cools stator  2  which is heated as a result of the conversion losses. This heated oil stream then flows along stator  2  and drips away, together with the oil streams  30 ,  31 , through outflow bore  32  and at the front lower end of the gearbox housing part  28 .  
         [0037]     The number of necessary rotor bores depends on what is calculated for the individual application case. As a result, rotor bores which are arranged diametrically with respect to one another may be provided. In addition, three rotor bores which are arranged offset with respect to one another by 120• may be provided. In addition, four rotor bores which are arranged offset with respect to one another by 90• may be provided. The important factor here is a uniform arrangement which prevents unbalance of the rotor.  
         [0038]     The gearbox may in particular be a planetary automatic transmission with laminated clutches/brakes which can be engaged and disengaged by means of the pressure of the aforesaid oil pump.  
         [0039]     In addition, the gearbox may be an automatic idler shaft gearbox whose shifting sleeves are activated at least indirectly with the pressure of the oil pump. A special form of such an idler shaft gearbox is the double clutch gearbox. The shifting sleeves may activate either shifting claws or synchromesh rings. In particular, the pressure of the oil pump can activate a shifting shaft or shifting rails for activating shifting forks/shifting rockers.  
         [0040]     The gearbox can also be an infinitely variable automatic transmission such as, for example, a toroidal gearbox.  
         [0041]     In a further embodiment, the axial support of the stator by means of a circlip DIN  472  and a plate may be dispensed with. In particular in this case, the stator can be connected to the gearbox housing part  28  so as to be fixed in terms of rotation and axially nondisplaceable by means of a formfit. In this context, the stator is composed of a laminated steel core and the gearbox housing part  28  is composed of a material which has a coefficient of thermal expansion α which corresponds at least approximately to the coefficient of thermal expansion α of the laminated steel core. This material may be in particular a nonlight metal containing a large amount of iron, for example a gray cast iron casting or a steel casting. Due to the proximity of the coefficient of thermal expansion α of the laminated core to the coefficient of thermal expansion a of the gearbox housing part  28 , the form-fit configuration is insured over a wide temperature range to be covered. Such a wide temperature range occurs between the cold start and continuous operation of the hybrid vehicle. A gearbox housing which is fitted with the transmission means such as, for example, gearwheels or a stepless variator, may be composed herein particularly of aluminum or even magnesium and connected by flanges to gearbox housing part  28 .  
         [0042]     The embodiments described are only exemplary configurations. A combination of the described features for different embodiments is also possible. Further features, in particular features which are not described, of the device parts associated with the invention can be found in the geometries of the device parts which are illustrated in the drawings.