Abstract:
An electromechanical transmission is provided with a structural support member that supports a motor/generator in a space efficient way; particularly, the motor/generator is supported from one side only to save space axially in the transmission. Specifically, a stationary structural support member circumscribes an outer surface of and supports a stator while extending radially-inward of a rotor and at least partially supporting the rotor. A rotor hub rotatable with respect to the structural support member is used to support an inner surface of the rotor. The structural support member substantially encloses the stator and rotor from one direction along the axis of rotation. However, the stator and rotor have no additional support members in the opposing axial direction such that they are unenclosed from an opposing axial direction.

Description:
TECHNICAL FIELD 
     The invention relates to a structural support member for a stator and a rotor of a motor/generator in an electromechanical transmission. 
     BACKGROUND OF THE INVENTION 
     Electromechanical transmissions such as electrically variable transmissions (EVTs) are constructed with differential gearing, which is typically one or more planetary gear sets, and at least one but typically two electric motor/generators. In an EVT, a motor/generator is connected with a member of a differential gear set to provide a variable ratio through the gear set, as is well understood by those skilled in the art. The combination of differential gearing and electric motor/generators potentially requires a longer axial length than a conventional automatic transmission utilizing differential gearing and clutches rather than electric motor/generators. 
     SUMMARY OF THE INVENTION 
     An electromechanical transmission is provided with a structural support member that supports a motor/generator in a space efficient way; particularly, the motor/generator is supported from one side only to save space along the axis of rotation of the transmission. 
     Specifically, an electromechanical transmission within the scope of the invention includes an annular rotor that is rotatable about an axis of rotation. An annular stator circumscribes the rotor. A stationary structural support member circumscribes an outer surface of the stator and supports the stator. The structural support member extends radially-inward of the rotor and at least partially supports the rotor. A rotor hub is used to support an inner surface of the rotor and is rotatable with respect to the stationary support member. The structural support member substantially encloses the stator and rotor from one direction along the axis of rotation. However, the stator and rotor have no additional support members in the opposing axial direction such that they are unenclosed from an opposing axial direction. 
     In one aspect of the invention, the structural support member has an extended rim, an outer surface of which is supported within a transmission case that circumscribes the stator and rotor by contact with the transmission case (e.g., by a press-fit with the transmission case). The stator is then supported at an inner surface of the extended rim. Thus, the motor/generator may be assembled within the stationary structural member that then may be press-fit within the transmission case. 
     In another aspect of the invention, the structural support member is a portion of the transmission case. Thus, the structural support member and the transmission case are unitary. 
     In yet another aspect of the invention, a single stationary support member circumscribes and supports two separate motor/generators. In that instance, the structural support member extends radially between the two motor/generators. Thus, adjacent sides of the motor/generators are enclosed by the structural support member. The non-adjacent (outer) sides of the motor/generators are substantially un-enclosed and are not supported by any structural support members. 
     In yet another aspect of the invention, a differential gear set having a first, a second and a third member is rotatable about the axis of rotation. The differential gear set is preferably a planetary gear set with the first, second and third members being a sun gear member, a carrier member and a ring gear member. The gear set is positioned axially between the first and second motor/generators and at least one of the members is operatively connected to one of the rotors. Thus, space between the motor/generators not only houses the structural support member but also one or more planetary gear sets. 
     In a further aspect of the invention, one or more bearings are located between the rotor hub and the structural support member to enhance rotation of the rotor hub with respect to the structural support member. The bearing or bearings are located axially between planes perpendicular to the axis of rotation at respective opposing extremities of side surfaces of the rotor. Thus, the bearings are positioned to decrease a moment imposed thereon by the rotation of the rotor. Preferably, the bearing is a ball bearing and is an angular contact type ball bearing. The bearing may have multiple rows of axially-spaced balls between a single pair of races. Alternatively, separate bearings having separate races, preferably also of the angular contact type, may be employed. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic partially cross-sectional side view of an electromechanical transmission having a structural support member within the scope of the invention; 
         FIG. 2  is a schematic partially cross-sectional side view illustration of a second embodiment of an electromechanical transmission utilizing separate structural support members for first and second motor/generators; 
         FIG. 3  is a third embodiment of a transmission within the scope of the transmission utilizing separate first and second structural support members for first and second motor/generators; 
         FIG. 4  is a cross-sectional view of a multi-row, angular contact ball bearing used in the transmission of  FIG. 1 ; and 
         FIG. 5  is a cross-sectional view of single row, angular contract bearings used in the transmission of  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows an electromechanical transmission  10  having a transmission case  12 . As described below, the transmission case  12  serves as a stationary structural support member  13 . The structural support member  13  circumscribes and only partially encloses first and second motor/generators  14 A and  14 B, respectively. The first motor/generator  14 A includes a rotor  16 A with an inner surface  18 A supported for rotation by a rotor hub  20 A about an axis of rotation C of main shaft  17 . 
     The first motor/generator  14 A further includes a stator  22 A. Stator  22 A annularly circumscribes the rotor  16 A. An outer surface  24 A of the stator  22 A is supported by a press-fit within the structural support member  13 . 
     The second motor/generator  14 B includes like components including a second rotor  16 B, an inner surface of which  18 B is supported by a rotor hub  20 B. Additionally, the second motor/generator  14 B includes a stator  22 B with an outer surface  24 B supported at and press-fit within the structural support member  13 . 
     The transmission case  12  includes an outer annular portion  26 , an inner annular portion  28 , and a radially-extending radial hub portion  30  which extends inward of each of the rotors  16 A,  16 B. The annular portions  26  and  28  and the radial hub portion  30  form the stationary structural support member  13 . In the embodiment of  FIG. 1 , the transmission case  12  is unitary with and forms the structural support member  13 . Additionally, a structural support member within the scope of the invention may be a separate component from the transmission case, as described below with respect to the embodiments of  FIGS. 2 and 3 . 
     Bearings  32 A,  32 B are employed on the first and second motor/generators  14 A,  14 B, respectively, to enhance rotation of the rotors hubs  20 A,  20 B and therefore the rotors  16 A,  16 B with respect to the inner annular portion  28  of the structural support member  13 . The bearing  32 A is located axially between first and second planes, P 1 , P 2 , that are perpendicular to the axis of rotation C at opposing first and second extremities  40 A,  42 A of first and second opposing side surfaces  44 A,  46 A of the first rotor  16 A. An “extremity” of a side surface of the rotor is the point or points on the side surface furthest axially from a vertical centerline through the rotor. Preferably, the bearings  32 A are angular-contact, multiple row bearings as shown in and discussed with respect to  FIG. 4 , below. 
     The bearings  32 B are similarly located, axially between first and second opposing planes P 3 , P 4  that are perpendicular to the axis of rotation C at opposing first and second extremities  40 B,  42 B, of first and second opposing side surfaces  44 B,  46 B, respectively, of the second rotor  16 B. Thus, any moment on the bearings  32 A,  32 B generated by rotation of the rotors  16 A,  16 B is minimal in comparison to a moment on bearings that are axially-spaced from a motor/generator and not positioned axially within planes at outer side surfaces of the rotor. The angular contact bearing design of the bearings  32 A,  32 B of  FIG. 1  is shown and described in detail with respect to  FIG. 4  below. 
     The electromechanical transmission  10  also includes first and second differential gear sets  50 A,  50 B. The differential gear set  50 A includes a sun gear member  52 A, a ring gear member  54 A, and a carrier member  59 A that rotatably supports a plurality of pinion gears  56 A meshingly engaged with both the sun gear member  52 A and ring gear member  54 A. Those skilled in the art will readily understand the structure and function of the components of a planetary gear set. For instance, various members of the gear sets  50 A,  50 B may be interconnected, or may be selectively connectable with one another or with the transmission case  12  via clutches or brakes (not shown). The second planetary gear set  50 B includes like first, second and third members such as sun gear member  52 B, ring gear member  54 B and carrier member  59 B that rotatably supports a plurality of pinion gears  56 B in meshing engagement with the sun gear member  52 B and ring gear member  54 B. In this embodiment, the planetary gear sets  50 A and  50 B are located axially with respect to the motor/generators  14 A,  14 B opposite the centrally-located structural support member  13 . 
     The motor/generator  14 A is enclosed by the structural support member  13  from an axial direction along axis of rotation C looking leftward in  FIG. 1  but is unenclosed by any structural support member when looking rightward along axis C in  FIG. 1 . Motor/generator  14 B is enclosed by structural support member  13  when looking leftward along centerline C in  FIG. 1  but is unenclosed and not supported by any structural support member when looking rightward along axis C in  FIG. 1 . The centrally-located structural support member  13  of  FIG. 1  thus does not interfere with packaging space for gear sets  50 A and  50 B. 
     Referring to  FIG. 2 , electromechanical transmission  100  has a transmission case  112 . A stationary structural support member  113 A circumscribes and only partially encloses a first motor/generator  114 A. The first motor/generator  114 A includes a rotor  116 A with an inner surface  118 A supported for rotation by a rotor hub  120 A about an axis of rotation C′ of main shaft  117 . 
     The first motor/generator  114 A further includes a stator  122 A. Stator  122 A annularly circumscribes the rotor  116 A. An outer surface  124 A of the stator  122 A is supported by a press-fit within the structural support member  113 A. 
     The second motor/generator  114 B includes like components including a second rotor  116 B that has an inner surface  118 B supported by a rotor hub  120 B. Additionally, the second motor/generator  114 B includes a stator  122 B with an outer surface  124 B supported at and press-fit within a stationary structural support member  113 B. The stationary structural support member  113 B circumscribes and only partially encloses the second motor/generator  114 B. 
     The structural support member  113 A includes an outer annular portion  126 A, an inner annular portion  128 A, and a radially-extending radial hub portion  130 A which extends radially-inward of the rotor  116 A. The annular portions  126 A and  128 A and the radial hub portion  130 A form the stationary structural support member  113 A. Similarly, the structural support member  113 B includes an outer annular portion  126 B, an inner annular portion  128 B, and a radially-extending radial hub portion  130 B which extends radially-inward of the rotor  116 B. The annular portions  126 B and  128 B and the radial hub portion  130 A form the stationary structural support member  113 B. 
     Bearings  132 A,  132 C are employed on the first motor/generator  114 A to enhance rotation of the rotor hub  120 A and therefore of the rotor  116 A with respect to the inner annular portion  128 A of the structural support member  113 A. The bearings  132 A and  132 C are located axially between planes that are perpendicular to the axis of rotation C′ at opposing first and second extremities  140 A,  142 A of first and second opposing side surfaces  144 A,  146 A of the first rotor  116 A. Preferably, the bearings  132 A and  132 C are angular-contact, single row bearings as discussed below with respect to  FIG. 5 . 
     Bearings  132 B,  132 D are employed on the second motor/generator  114 B to enhance rotation of the rotor hub  120 B and therefore of the rotor  116 B with respect to the inner annular portion  128 B of the structural support member  113 B. The bearings  132 B,  132 D are similarly located, axially between opposing planes that are perpendicular to the axis of rotation C′ at opposing first and second extremities  140 B,  142 B, of first and second opposing side surfaces  144 B,  146 B, respectively, of the second rotor  116 B. Thus, any moment on the bearings  132 A,  132 B generated by rotation of the rotors  116 A,  116 B is minimal in comparison to a moment on bearings that are axially-spaced from a motor/generator and not positioned axially within planes at outer side surfaces of the rotor. 
     The electromechanical transmission  10  also includes first and second differential gear sets  150 A,  150 B. The differential gear sets  150 A and  150 B include a sun gear member, a ring gear member, and a carrier member that rotatably supports a plurality of pinion gears meshingly engaged with both the sun gear member and ring gear member similar to the planetary gear set  50 A of  FIG. 1 . An additional planetary gear set  150 C is packaged axially between the radial-extending portions  130 A,  130 B of the structural support members  113 A,  113 B. The planetary gear set  150 C includes a ring gear member  154 C, a sun gear member  152 C and a plurality of pinion gears  156 C rotatably supported on a carrier member  159 C and in meshing engagement with both the sun gear member  152 C and the ring gear member  154 C. Those skilled in the art will readily understand the structure and function of the components of a planetary gear set. For instance, various members of the gear sets  150 A- 150 C may be interconnected, or may be selectively connectable with one another or with the case  112  via clutches or brakes (not shown). In this embodiment, the planetary gear sets  150 A and  150 B are located axially with respect to the motor/generators  114 A,  114 B opposite the centrally located structural support members  113 A,  113 B and the planetary gear set  150 C. 
     The motor/generator  114 A is enclosed by the structural support member  113 A from an axial direction along axis C′ looking leftward in  FIG. 2  but is unenclosed by any structural support member when looking rightward along axis C′ in  FIG. 2 . Motor/generator  114 B is enclosed by structural support member  113 B when looking leftward along axis C′ in  FIG. 2  but is unenclosed and not supported by any structural support member when looking rightward along axis C′ in  FIG. 2 . The structural support members  113 A,  113 B are configured to provide the open space therebetween in which gear set  150 C is packaged. 
     Referring to  FIG. 3 , an electromechanical transmission  200  has a transmission case  212 . A structural support member  213 A circumscribes and only partially encloses a first motor/generator  214 A. The first motor/generator  214 A includes a rotor  216 A with an inner surface supported for rotation by a rotor hub  220 A about an axis of rotation C″ of main shaft  217 . 
     The first motor/generator  214 A further includes a stator  222 A. Stator  222 A annularly circumscribes the rotor  216 A. An outer surface of the stator  222 A is press-fit within the structural support member  213 A. The structural support member  213 A is bolted to the transmission case  212  via circumferentially spaced bolts  227 A (one shown). 
     The second motor/generator  214 B includes like components including a second rotor  216 B, an inner surface of which is supported by a rotor hub  220 B. Additionally, the second motor/generator  214 B includes a stator  222 B with an outer surface supported at and press-fit within an outer annular portion  226 B of a structural support member  213 B. The structural support member  213 B is bolted to the transmission case via circumferentially spaced bolts  227 B (one shown). 
     The structural support member  213 A includes an outer annular portion  226 A, an inner annular portion  228 A, and a radially-extending radial hub portion  230 A that extends radially-inward of the rotor  216 A. The annular portions  226 A and  228 A and the radial hub portion  230 A form the stationary structural support member  213 A. Similarly, the structural support member  213 B includes an outer annular portion  226 B, an inner annular portion  228 B, and a radially-extending radial hub portion  230 B that extends radially-inward of the rotor  216 B. The annular portions  226 B and  228 B and the radial hub portion  230 B form the stationary structural support member  213 B. Sensor wheels  223 A,  223 B are used to determine the rotational speeds of the rotors  216 A,  216 B. 
     Bearings  232 A,  232 C are employed on the first motor/generators  214 A to enhance rotation of the rotor hubs  220 A and therefore the rotors  216 A with respect to the inner annular portion  228 A of the structural support member  213 A. The bearings  232 A,  232 C are located axially between first and second planes that are perpendicular to the axis of rotation C″ at extremities of opposing side surfaces of the first rotor  216 A. Preferably, the bearings  232 A,  232 C are angular-contact, single row bearings as shown in and discussed with respect to  FIG. 5 , below. 
     The bearings  232 B,  232 D are similarly located, axially between opposing planes that are perpendicular to the axis of rotation C″ at extremities of opposing side surfaces of the second rotor  216 B. Thus, any moment on the bearings  232 A- 232 D generated by rotation of the rotors  216 A,  216 B is minimal in comparison to a moment on bearings that are axially-spaced from a motor/generator and not positioned axially within planes at outer side surfaces of the rotor. The angular contact bearing design of the bearings  232 B,  232 D is shown and described in detail with respect to  FIG. 5  below. Bearings  232 A and  232 C are depicted In  FIG. 3  as angular contact, single row bearings. 
     The electromechanical transmission  200  also includes a differential gear set  250 C. The differential gear set  250 C includes a sun gear member  252 C, a ring gear member  254 C, and a carrier member  259 C that rotatably supports a plurality of pinion gears  256 C meshingly engaged with both the sun gear member  252 C and ring gear member  254 C. The ring gear member  254 C is continuously connected with the rotor  216 A via the rotor hub  220 A and an interconnecting member  257 . The carrier member  259 C is continuously connected with the main shaft  217 . The sun gear member  252 C is continuously connected with the rotor  216 B via the rotor hub  220 B and sleeve shaft  221 . Additional planetary gear sets (not shown) may be packaged on opposite sides of the motor/generators  214 A,  214 B similar to planetary gear sets  150 A and  150 B of  FIG. 2 . Members of the planetary gear sets may be interconnected continuously or selectively via clutches or brakes with one another or with the transmission case, as is understood by those skilled in the art, to establish fixed ratio or variable operating modes of the transmission. 
     Referring to  FIG. 4 , the bearing  32 A of  FIG. 1  is shown between the rotor  20 A and the structural support member  13  (specifically, the inner annular portion  28  of the structural support member, as shown in  FIG. 1 ). The bearing  32 A includes an outer race  60  and an inner race  62 . Two separate rows of ball bearings, represented by balls  58 A and  58 B are nested between the races  60 ,  62 . The races  60  and  62  are formed to provide angular contact with the balls  58 A,  58 B. That is, the center of contact between the races  60 ,  62  and the balls  58 A and  58 B is at an angle that supports an axial load as opposed to only a pure radial load that would be supported by standard races having contact with balls at a 90-degree angle to the axis of rotation. The angle of the contact is indicated by the angled centerlines of the balls  58 A,  58 B in  FIG. 4 . Angular contact ball bearings are designed to carry a heavier axial load than purely radial contact bearings. Bearings which firmly support axial loads also support moments on the rotor perpendicular to the axis of rotation, and suppress vibration of the rotor at high speeds. Similar angular contact, multi-row bearings may be used for bearing  32 B of  FIG. 1  or in lieu of the closely spaced but separate, single row angular contact bearings  232 A and  232 C of  FIG. 3 . 
     Referring to  FIG. 5 , the bearings  232 B and  232 D of  FIG. 3  are shown between rotor  220 B and structural support member  213 B (specifically, the inner annular portion  228 B of structural support member  213 B, as shown in  FIG. 3 ). The bearing  232 B includes an outer race  260 B and an inner race  262 B. The bearing  232 D includes an outer race  260 D and an inner race  262 D. A single row of balls  258 B is nested between the outer and inner races  260 B,  262 B and a single row of balls  258 D is nested between the outer and inner races  260 D,  262 D. The races  260 B and  262 B are formed to provide angular contact with the balls  258 B. Similarly, the races  260 D and  262 D are formed to provide angular contact with the balls  258 D. The angle of contact is indicated by the angled centerlines of the balls  258 B,  258 D in  FIG. 5 . Similar angular contact, single row bearings may be used in lieu of the bearings  132 A- 132 D of  FIG. 2 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.