Abstract:
A transmission includes a housing, an electric motor having a stator within the housing, and a member including a generally cylindrical portion that circumscribes at least part of the stator. The member cooperates with the housing to form an annular coolant flowpath therebetween, and the member includes a plurality of holes to provide radial inflow of coolant from the flowpath to the stator to provide significantly improved motor cooling compared to the prior art.

Description:
TECHNICAL FIELD 
     This invention relates to transmissions that include at least one electric motor, a housing, and a member that at least partially circumscribes the motor and cooperates with the housing to form an annular flowpath. 
     BACKGROUND OF THE INVENTION 
     Electrically variable transmissions, such as those described in U.S. Pat. No. 5,931,757, employ two electric motors mounted inside a transmission housing. The electric motors are coaxially oriented with an input shaft, an output shaft, and two planetary gearsets. Each motor is operatively connected to a member of one of the planetary gearsets to provide a range or mode of transmission operation characterized by a continuously variable speed ratio between the input shaft and the output shaft. 
     The electric motors in electrically variable transmissions must have very precise location, low sensitivity of location to thermal events, and very uniform coolant flow. Thus, manufacturing tolerances for components, such as the housing, that interface with the motors are typically small and, accordingly, limit the manufacturing processes that may be employed. 
     SUMMARY OF THE INVENTION 
     An electrically variable transmission is provided. The transmission includes a transmission housing defining a generally cylindrical cavity. The transmission also includes an electric motor located within the cavity. The electric motor includes a generally ring-shaped stator and a rotor. The transmission also includes a member having a generally cylindrical portion that circumscribes at least a portion of the stator. The member and the housing define an annular coolant flowpath therebetween, and the member includes a plurality of holes formed therein so that coolant in the annular flowpath flows radially inward toward the stator windings to provide a concentric radial spray feature. Concentric radial spray of coolant provides superior cooling of the stator windings compared to other methods available in the prior art, and therefore enables the motor to be smaller compared to the prior art. 
     In a preferred embodiment, the stator is mounted to the member rather than the housing, thus enabling larger manufacturing tolerances for the housing. The member thus enables the housing to be formed using manufacturing processes, such as die casting, suitable for high-volume production. 
     In a preferred embodiment, the transmission includes two motors mounted to the member to form a preassembled module for simplified assembly. The module enables insertion of the motors into the housing from one direction, and allows both of the stators, speed sensors, and wiring to be subassembled and tested prior to insertion into the housing. The module also provides ease of replacement during transmission servicing. The preassembled module enables a reduced transmission diameter compared to the prior art because the module, including both motors, may be fastened to the housing at the forward end and not at the rearward end, thus eliminating the rearward split-line. 
     The member is preferably steel to prevent thermal clearance changes, to allow standard clearance bearings, and to provide electromagnetic shielding for speed sensors, i.e., speed resolvers, that monitor rotor speed and the wires of speed sensors. 
     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 cross-sectional side view of a portion of an electrically variable transmission; 
         FIG. 2  is a schematic perspective view of the transmission portion of  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional side view of an alternative transmission configuration according to the claimed invention; 
         FIG. 4  is a schematic cross-sectional side view of a portion of another alternative transmission configuration, including a transmission housing and a motor module operatively connected thereto; and 
         FIG. 5  is a schematic cross-sectional side view of a portion of the transmission of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a portion of an electrically variable transmission  10  is schematically depicted. Exemplary electrically variable transmissions are described in U.S. Pat. No. 5,558,595, issued Sep. 24, 1996 to Schmidt et al; U.S. Pat. No. 5,931,757, issued Aug. 3, 1999 to Schmidt; U.S. Pat. No. 6,478,705, issued Nov. 12, 2002 to Holmes et al; and U.S. Pat. No. 6,527,658, issued Mar. 4, 2003 to Holmes et al, each of which is hereby incorporated by reference in its entirety. The transmission  10  includes a housing  14  that defines the exterior surface  18  of the transmission. The housing  14  includes an inner surface  22  that defines a generally cylindrical cavity  26 . 
     The transmission  10  also includes a first electric motor/generator  30 A and a second electric motor/generator  30 B. Each electric motor generator  30 A,  30 B includes a generally ring-shaped stator  34 A,  34 B fixed with respect to the housing  14 , and a rotor  38 A,  38 B. The motors  30 A,  30 B are coaxially aligned with an input shaft (not shown) and a plurality of planetary gearsets  42 A,  42 B. The motors  30 A,  30 B are operatively connected to the gearsets  42 A,  42 B in a manner similar to that described in the aforereferenced patents. 
     The transmission housing  14  includes a wall  46  extending radially-inwardly toward the transmission centerline  50  from the inner surface  22 . The wall  46  separates the stator  34 A of the first motor  30 A from the stator  34 B of the second motor  30 B, and includes a formation  54  for receiving threaded fasteners  58 . A member  62 A is affixed to the wall  46  at the formation  54  by threaded fastener  58 . The member  62 A includes a generally cylindrical portion  66 A that circumscribes at least part of stator  34 A, and cooperates with the housing  14  to form an annular coolant flowpath  70 A therebetween. The annular coolant flowpath  70 A is in fluid communication with a source of pressurized fluid coolant. The member  62 A defines a plurality of holes  74  sufficiently positioned to direct coolant from the annular coolant flowpath  70 A radially inward toward the stator  34 A. O-rings or other seals  78  are employed between the member  62 A and the housing  14  to seal the annular flowpath  70 A. 
     A similar member  62 B is mounted to the wall  46  at the formation  54  by a threaded fastener  58  to circumscribe at least a portion of stator  34 B with a generally cylindrical portion  66 B. Member  62 B also cooperates with the housing  14  to form an annular flowpath  70 B, and includes holes  74  formed therein to direct coolant from the flowpath  70 B radially inward toward the stator  34 B. Support members  82  are affixed to the wall  46  by fasteners  58  to rotatably support rotors  38 A,  38 B at bearings  86 . The stators  34 A,  34 B are preferably staked to the members  62 A,  62 B. The members  62 A,  62 B are preferably sized to maintain a light press on the stators. 
       FIG. 2 , wherein like reference numbers refer to like components from  FIG. 1 , is a schematic perspective illustration of a portion of housing  14  and member  62 A. Only a portion of the rotor  38 A of motor  30 A is depicted in  FIG. 2 . 
     Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , an alternative transmission  10 ′ and member configuration is schematically depicted. Members  62 A′,  62 B′ are each attached to opposite sides of housing wall  46 ′, such as by threaded fastener, rivet, physical part interference caused by the stators  34 A′,  34 B′, etc. 
     Members  62 A′,  62 B′ each include respective outer walls  90 A,  90 B that cooperate with the housing  14 ′ to form annular flowpaths  70 A′,  70 B′. The members  62 A′,  62 B′ also include respective inner walls  94 A,  94 B. Inner wall  94 A is positioned with respect to the outer wall  90 A such that an open space  98 A is formed therebetween that contains a portion of stator  34 A′. Similarly, inner wall  94 B is positioned with respect to outer wall  90 B such that an open space  98 B is formed therebetween that contains a portion of stator  34 B′. Inner walls  94 A,  94 B each have a bearing  86  mounted thereto to rotatably support rotors  38 A′,  38 B′. Inner walls  94 A,  94 B also support speed resolvers  102  for monitoring the speed of the rotors. 
     Referring to  FIG. 4 , wherein like reference numbers refer to like components from  FIGS. 1-3 , another alternative transmission  10 ″ configuration is schematically depicted. The transmission  10 ″ includes a preassembled module  106  that includes member  110  and two motors  30 A″,  30 B″, of which only the respective stators  34 A″,  34 B″ are depicted in  FIG. 3 . The member  110  includes an outer wall  114 , the outer surface  118  of which cooperates with the housing  14 ″ to define annular flowpaths  70 A″,  70 B″. Inner surface  122  of outer wall  114  defines a generally cylindrical space  126  in which the stators  34 A″,  34 B″ of motors  30 A″,  30 B″ are located. Member  110  also includes wall  130  that extends radially inward from inner surface  122 . Inner wall  134  extends axially from wall  130 , and is spaced a distance from outer wall  114 . A portion of stator  34 A″ is between the outer wall  114  and inner wall  134 . A portion of stator  34 B″ is between the outer wall  114  and inner wall  134 . Bearings  86  are attached to inner wall  134  to rotatably support the rotors of motors  30 A″,  30 B″. Speed resolvers  102  are also affixed to the inner wall  134 . Hole  138  is formed in wall  130  through which wiring  142  for speed resolvers extend. Member  110  is preferably steel to prevent thermal clearance changes, to allow standard clearance bearings, and to provide electromagnetic shielding for the resolvers and wires. 
     Referring to  FIG. 5 , wherein like reference numbers refer to like components from  FIGS. 1-4 , the member  110  of module  106  preferably includes a flange  146 . The member  110  is mountable to the housing  14 ″ at the flange  146  using the same bolt  58  that is used to connect the transmission front transmission support assembly  150 . 
     Commonly-assigned U.S. Patent Application Ser. Nos. 60/555,141, filed Mar. 22, 2004, and 60/555,270, filed Mar. 22, 2004, are hereby incorporated by reference in their entireties. 
     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.