Patent Publication Number: US-11394270-B2

Title: Differential for an active core electric motor having pin with friction fit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/182,755, filed Nov. 7, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 16/181,612, filed 6 Nov. 2018, now U.S. Pat. No. 10,797,562, which claims benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/766,523, filed 23 Oct. 2018, the disclosures of which are incorporated herein by reference for any and all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to electric motors and, more particularly, to a removable differential assembly for use in an active core electric motor. 
     BACKGROUND OF THE INVENTION 
     In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drivetrains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drivetrain, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost. 
     The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drivetrain in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at a reduced level compared to a conventional vehicle. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drivetrain of a hybrid vehicle is typically more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, thereby eliminating one source of pollution while significantly reducing drivetrain complexity. 
     While a variety of hybrid and all-electric vehicles are known, a high power density powertrain that fits within a reduced envelope is desired in order to increase the available space for occupants, cargo, and other vehicle components/accessories. One method of achieving a reduced powertrain envelope is to coaxially align the traction motor with the drive wheel axes using a planetary-differential-planetary configuration. In such a design, the differential may be integrated within the rotor of the electric motor, this configuration being commonly referred to as an active core motor. While this approach allows a compact powertrain assembly to be achieved, the durability and serviceability of the internally mounted differential can affect both the performance and reliability of an electric vehicle (EV) utilizing such an assembly. Accordingly, the present invention provides a durable and easily accessible/serviceable differential assembly for an active core motor. 
     SUMMARY OF THE INVENTION 
     The present invention provides a gear assembly that is configured for integration within the hollow rotor of an electric motor. The gear assembly includes a hollow cross member, a plurality of gears, and a plurality of pins. The hollow cross member of the assembly includes a central body portion, a central body thru-hole within the central body portion, and a plurality of hollow extension members that extend outwards from the central body portion, where each hollow extension member is in fluid communication with the centrally located thru-hole. Preferably the hollow extension members are comprised of four hollow extension members that are uniformly spaced about the central body portion of the hollow cross member. The plurality of gears is configured to be mounted on the plurality of hollow extension members. Each of the plurality of pins is configured to slide within a corresponding hollow extension member and is positionable between a first, withdrawn position and a second, extended position. When the pins are extended, a first end portion of each pin fits within a corresponding aperture in the hollow rotor and the centrally located thru-hole is coaxially aligned with the rotor axis. When the pins are withdrawn, the hollow cross member fits unimpeded into the hollow rotor. A plug member may be configured to fit within the central body thru-hole when each of the pins is in the second, extended position. The plug member may include a thru-hole, and the plug member thru-hole may be coaxially aligned with the rotor axis when the plug member is mounted within the central body thru-hole of the central body portion of the hollow cross member. 
     In one aspect, a second end portion of each pin, which is inwardly directed towards the central body thru-hole of the central body portion of the hollow cross member, may be tapered. 
     In another aspect, the gear assembly may include a plurality of spring members (e.g., bevel springs). These spring members are interposed between each of the gears and the corresponding face of the central body portion of the hollow cross member. 
     In another aspect, the gear assembly may include a plurality of washers (e.g., friction washers), each of which is mounted to the end portion of a corresponding hollow extension member. As a result, when the gears are mounted to the hollow cross member, each of the gears is interposed between one of the washers and the central body portion of the hollow cross member. The end portion of each of the hollow extension members may include at least one anti-turn tab that fits within a complementary feature on a corresponding washer, the anti-turn tab preventing the washer from rotating. 
     A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       It should be understood that the accompanying figures are only meant to illustrate, not limit, the scope of the invention and should not be considered to be to scale. Additionally, the same reference label on different figures should be understood to refer to the same component or a component of similar functionality. 
         FIG. 1  provides a cross-sectional view of a powertrain assembly incorporating the differential assembly of the invention; 
         FIG. 2  provides a detailed cross-sectional view of the differential gear assembly of the invention mounted within a hollow rotor shaft; 
         FIG. 3  provides a perspective cross-sectional view of the assembly shown in  FIG. 2 ; 
         FIG. 4  provides a perspective front view of a portion of the differential gear assembly shown in  FIGS. 1-3 , this view only showing two of the gears and three of the radial pins in place; 
         FIG. 5  provides a perspective rear view of a portion of the differential gear assembly shown in  FIGS. 1-3 , this view only showing two of the gears and three of the radial pins in place; 
         FIG. 6  provides a cross-sectional view of the assembly shown in  FIG. 5 , where this view is orthogonal to the cross-sectional view shown in  FIG. 2 ; and 
         FIG. 7  provides a perspective cross-sectional view of the differential gear assembly shown in  FIGS. 1-6 , this view showing all four gears in place and all four of the radial pins removed. 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “includes”, and/or “including”, as used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” and the symbol “/” are meant to include any and all combinations of one or more of the associated listed items. Additionally, while the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms, rather these terms are only used to distinguish one step or calculation from another. For example, a first calculation could be termed a second calculation; similarly a first step could be termed a second step; similarly a first component could be termed a second component, all without departing from the scope of this disclosure. 
       FIG. 1  provides a cross-sectional view of a powertrain assembly  100  that incorporates a differential gear assembly  101  within hollow rotor shaft  103 , where differential assembly  101  is designed in accordance with the invention. Utilizing the active core configuration, powertrain assembly  100  is arranged such that planetary assembly  105 , differential gear assembly  101 , and planetary assembly  107  are coaxially aligned, thereby creating a powertrain with a relatively short width  109 , where width  109  is measured between the bottom surfaces  111  of the two constant velocity (i.e., CV) joint housing members. 
     Although not required by the invention, in the illustrated assembly hollow rotor shaft  103  is directly connected to the rotor lamination stack, thereby achieving a high speed motor proportion configuration suitable for use in an electric vehicle (EV). In the illustrated embodiment, the lamination stack is comprised of four lamination pack layers  113 A- 113 D. It should be understood that this lamination stack configuration is not required by the invention. Surrounding the rotor lamination stack is stator  115 . Visible in this view are the stator windings  117  that extend from either end of the stator. 
     As described in detail below, the present invention provides a removable differential gear assembly  101  that is configured to be mounted within the rotor of an electric motor. Output drive shafts  119  are coupled to differential assembly  101  using gears  121 . 
       FIG. 2  provides a detailed cross-sectional view of differential gear assembly  101  mounted within rotor shaft  103 .  FIG. 3  provides a perspective cross-sectional view of the assembly shown in  FIG. 2 .  FIGS. 4 and 5  provide perspective front and rear views, respectively, of a portion of gear assembly  101 , these views only showing two of the gears and three of the radial pins in place.  FIG. 6  is a cross-sectional view of the assembly shown in  FIG. 5 . Note that the cross-sectional view shown in  FIG. 6  is orthogonal to the cross-sectional view shown in  FIG. 2 .  FIG. 7  provides a perspective cross-sectional view of assembly  101  with all four gears in place and all four of the radial pins removed. 
     The primary component of assembly  101  is a hollow cross member  601 , best viewed in  FIGS. 6 and 7 . The central body of cross member  601  includes a thru-hole  603 . Preferably thru-hole  603  is cylindrically shaped, and more preferably thru-hole  603  is cylindrically shaped and coaxial with rotor axis  201  as shown. In the preferred embodiment, a plug  203  that has a complementary shape to that of thru-hole  603  is configured to fit within thru-hole  603  of cross member  601 . Preferably plug  203  includes a thru-hole  205 . Thru-hole  205 , which is preferably coaxial with rotor axis  201  as well as the cylindrical axis of plug  203 , allows fluid to flow easily from one side of the differential assembly to the other, for example between output drive shafts  119 . Typically a suitable gear oil flows through thru-hole  205 , this oil lubricating the differential assembly as well as other components within the powertrain. 
     Extending outwards from the body of cross member  601  are multiple hollow extensions  207 . The thru-hole  605  within each hollow extension  207  extends into, and is in fluid communication with, the central aperture  603  of cross member  601 . The length  607  of each cross member extension  207  is selected to ensure that the cross member  601  can slide unimpeded into hollow rotor  103  during differential integration. In the preferred embodiment, there are four cross member extensions  207  that are uniformly spaced about the body of cross member  601 . It should be understood, however, that other configurations are envisioned by the inventors. For example, the assembly can utilize three hollow extensions  207  that are uniformly spaced about the body of cross member  601 . Similarly, the assembly can utilize a non-uniform spacing, for example four hollow extensions  207  with a spacing of 89 degrees, 91 degrees, 89 degrees, and 91 degrees. 
     Prior to installing the cross member into rotor shaft  103 , gears  209  and gear bearings  617  are installed on each cross member extension  207 . Preferably gears  209  are identical in size, shape and tooth count. As shown, gears  209  are selected such that there is a space  609  between adjacent gears, thus ensuring that the gears do not interfere with one another during operation. In the preferred embodiment, a washer (e.g., a friction washer)  611  is placed at the end of each cross member extension  207  after gear assembly. A tab  613 , which extends from a portion of the end surface of each cross member extension  207 , fits within a complementary opening  614  of washer  611 , thereby preventing washer  611  from rotating when the corresponding gear rotates. In at least one embodiment, a spring member  211  (e.g., a bevel spring or bushing) is placed between each gear  209  and the corresponding face  616  of cross member  601 . 
     Four pins  213  hold the differential assembly inside of the hollow rotor shaft  103 . Pins  213  fit within the cross member extensions  207  as shown, extending between the cross member and a corresponding thru-hole  215  in the rotor. As a result, the cross member assembly is locked into the rotor. Preferably the end portion  615  of each pin  213  is tapered, thus simplifying the assembly and disassembly processes. 
     It will be appreciated that there are multiple ways to insert the differential assembly into the rotor and then lock it into place. In one approach, after mounting gears  209  and bearings  617  onto the cross member extensions  207  (with or without spring member  211 , depending upon the configuration), pins  213  are placed within cross member extensions  207 . Then washers  611  are installed. At this stage of assembly, plug  203  is not located within cross member aperture  603 , thereby allowing pins  213  to be fully inserted into member  601 . When fully inserted, the ends of pins  213  do not extend beyond the end surfaces of extensions  207 . In this state, the differential assembly can be inserted into hollow rotor shaft  103 . Once the differential assembly is inserted into rotor  103 , pins  213  are aligned with the corresponding thru-holes  215  in the rotor. Once aligned, pins  213  are pushed outwards into rotor thru-holes  215 . A special tool may be inserted into cross member thru-hole  603 , causing pins  213  to be pushed outwards into the corresponding rotor thru-holes  215 . An exemplary tool is cylindrically-shaped with a tapered leading face configured to gently force the pins in an outwards direction. Alternately, plug  203  may be used to force the pins outwards into rotor thru-holes  215 . Pins  213  may be friction fit within rotor thru-holes  215 . Alternately and as preferred, once pins  213  have been fully inserted into thru-holes  215 , plug  203  is inserted into cross member thru-hole  603 , thereby locking pins  213  into place. This is the preferred assembly technique if the lamination stack, or other component, has already been mounted onto the rotor shaft. 
     In an alternate approach of assembling the differential-rotor assembly, after mounting spring members  211  (if used), gears  209 , bearings  617  and washers  611  onto the cross member extensions  207 , the cross member  601  is located within rotor shaft  103 . At this stage of assembly, pins  213  have not yet been inserted into the cross member. Preferably plug  203  has been inserted into cross member thru-hole  603 , although it can also be inserted into thru-hole  603  after the pins have been properly positioned within the cross member. Once cross member  601  is properly located in the rotor such that extension thru-holes  605  are aligned with rotor thru-holes  215 , pins  213  are pushed though the rotor thru-holes  215  and into the cross member extensions  207 . As previously noted, if plug  203  was not previously inserted into cross member thru-hole  603 , preferably it is inserted at this point in the assembly process. Once the pins are properly located, the lamination stack, or other component, is mounted onto the rotor shaft, thereby preventing the pins from falling out of the assembly. 
     Although not required, in at least one embodiment of the invention the end portion  615  of each pin  213  includes a small aperture  217  as seen in  FIGS. 2 and 3 . Aperture  217  allows a tool to be used to easily withdraw the pins into cross member  601  without removing the lamination stack, or other component, from the rotor. Thus if the differential assembly requires maintenance, it can be removed from the rotor without completely disassembling the rotor assembly. 
     Systems and methods have been described in general terms as an aid to understanding details of the invention. In some instances, well-known structures, materials, and/or operations have not been specifically shown or described in detail to avoid obscuring aspects of the invention. In other instances, specific details have been given in order to provide a thorough understanding of the invention. One skilled in the relevant art will recognize that the invention may be embodied in other specific forms, for example to adapt to a particular system or apparatus or situation or material or component, without departing from the spirit or essential characteristics thereof. Therefore the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention.