Abstract:
The present invention is drawn to a method and apparatus for cooling a hybrid transmission electric motor. More precisely, an annular chamber is formed between a housing for the electric motor and a transmission housing. Coolant is disposed in the annular chamber and is applied to the electric motor through a plurality of coolant apertures in the motor housing to cool the motor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/555,270, filed Mar. 22, 2004, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to a method and apparatus for cooling a hybrid transmission electric motor. 
     BACKGROUND OF THE INVENTION 
     The electric motors in a hybrid electro-mechanical transmission generate heat during operation. If the heat is not adequately dissipated, the performance and reliability of the motors may be impaired. 
     SUMMARY OF THE INVENTION 
     The present invention is drawn to a method and apparatus for cooling a hybrid transmission electric motor. A generally cylindrical motor housing having first and second engagement surfaces is provided. During assembly, the first and second engagement surfaces of the motor housing engage the transmission housing such that an annular chamber is formed therebetween. Pressurized coolant is disposed in the annular chamber through an access port in the transmission housing, and is thereafter applied to the stator windings of the electric motor through a plurality of coolant apertures in the motor housing. The pressurized coolant is preferably transmission fluid so that an additional coolant reservoir is not required. 
     According to a preferred embodiment, the first and second engagement surfaces each include an O-ring adapted to seal the annular cavity. A drain is disposed in the motor housing to prevent excess accumulation of coolant. The drain may be located at a height adapted to maintain a steady state level of accumulated coolant within the motor housing such that the electric motor is both cooled by the initial application of pressurized coolant and also by the accumulated coolant within the housing. A housing cover is preferably attached to the motor housing to enclose the electric motor and retain the accumulated coolant. 
     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 fragmentary cross-sectional view of a hybrid electro-mechanical transmission; 
         FIG. 2  is a schematic fragmentary cross-sectional view of a frontward portion of the transmission of  FIG. 1 ; 
         FIG. 3  is a schematic fragmentary cross-sectional view of a rearward portion of the transmission of  FIG. 1 ; 
         FIG. 4  is a schematic perspective view of a housing and attached cover for a motor module used in the transmission of  FIG. 1 ; and 
         FIG. 5  is a schematic cross-sectional view of a frontward portion of the transmission of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows the upper half of a transmission  10 , in cross sectional view. The lower half of the transmission (not shown) is disposed on the opposite side of center axis  12 . First and second electric motor modules  14 ,  16 , respectively, are disposed about the center axis  12  within the transmission  10 . A main shaft  20  is longitudinally disposed, rotatable about the center axis  12 . A plurality of inner shafts, such as inner shaft  22 , are concentrically disposed about the main shaft  20 , and are likewise rotatable about the center axis. An input shaft  24  is disposed forward of the main shaft  20  and is operable for transferring power from an engine (not shown) to the transmission  10 . Engagement of one or more of a plurality of clutches included in the transmission  10  (first, second, third and fourth clutches,  26 ,  28 ,  30  and  32  respectively, being shown) interconnects one or more of first, second and third planetary gear sets  34 ,  36 , and  38 , respectively, to transfer power at varying ratios to an output member (not shown). As will be readily understood by those skilled in the art, each of the planetary gear sets includes a sun gear member, a planet carrier assembly member and a ring gear member. A fifth clutch, referred to as a lockout clutch  42 , is operable for locking out torsion isolator  44  (also referred to as damper springs) from surrounding structural elements, and to provide a direct connection between the engine and transmission. 
     As shown in  FIGS. 2 and 3 , the first and second motor modules  14 ,  16  are self-contained assemblies. The motor modules  14 ,  16  each include a motor  46 A,  46 B, respectively. The motors  46 A,  46 B each include a rotor  48 A,  48 B and a stator  50 A,  50 B, respectively. The stator  50 A includes stator windings  79 A and  81 A, and similarly the stator  50 B includes stator windings  79 B and  81 B. It should be appreciated by one skilled in the art that the stator windings  79 A,  81 A,  79 B and  81 B generate heat during operation and therefore may be cooled to ensure optimal performance and reliability of the motors  46 A,  46 B. 
     The motors  46 A,  46 B are preferably enclosed within a drum  52 A,  52 B comprised of a generally cylindrical module housing  54 A,  54 B and a module housing cover  56 A,  56 B. Each module housing  54 A,  54 B includes an open end  58 A,  58 B adapted to facilitate the insertion of a motor, and an enclosed end  60 A,  60 B. The module housing covers  56 A,  56 B are respectively attached to the open end  58 A,  58 B of the module housing  54 A,  54 B after the motors  46 A,  46 B have been inserted therein as will be described in detail hereinafter. According to a preferred embodiment, the housing  54 A,  54 B is composed of formed steel and the cover  56 A,  56 B is stamped steel; however, it should be appreciated that the housing and cover may be composed of alternate materials and/or fabricated according to other known manufacturing processes. 
     Referring to  FIG. 3 , the housing  54 B defines an outer surface  62 B and an inner surface  64 B. The outer surface  62 B is generally linear with a raised portion  66 B near the open end  58 B of the housing  54 B. A first engagement surface  68 B adapted to engage the transmission housing  72 B is located near the enclosed end  60 B of the housing  54 B, and a second engagement surface  70 B adapted to engage the transmission housing  72 B is located on the raised portion  66 B of the outer surface  62 B. The portion of the outer surface  62 B between the first and second engagement surfaces is not in contact with the transmission housing  72 B and, as will be described in detail hereinafter, partially defines the annular cavity  74 B. To manufacture the housing  54 B using the preferred forming process, it may be necessary to machine the engagement surfaces  68 B,  70 B in order to maintain desired tolerances necessary for properly fitting the module housing  54 B within the transmission  10 . Advantageously, this embodiment provides a precision fit between the housing  54 B and the transmission  10  without the expense required to machine the entire outer surface  62 B. 
     The transmission housing  72 B includes a surface  76 B defining a motor cavity  78 B adapted to accommodate the module housing  54 B. The cavity surface  76 B preferably includes a draft angle of approximately 3 degrees to facilitate installation of the module housing  54 B. During installation, the first and second engagement surfaces  68 B,  70 B of the module housing  54 B engage the cavity surface  76 B such that the area axially defined between the first and second engagement surfaces  68 B,  70 B, and radially defined between the outer surface  62 B of the module housing  54 B and the cavity surface  76 B of the transmission housing  72 B, forms the annular cavity  74 B. Coolant  100  (shown in  FIG. 5 ) is introduced into the annular cavity  74 B through an access port  80 B in the transmission housing  72 B. The coolant  100  is preferably pressurized to facilitate the application thereof onto the motor  46 B; however, the coolant  100  may alternatively be applied using gravitational forces. The coolant  100  is preferably fluid from the transmission&#39;s cooling system (not shown) used to cool other transmission components; however, it should be appreciated that other fluids may be envisioned for this purpose. The implementation of fluid from the transmission cooling system is particularly advantageous because it does not require additional parts for storing, pressurizing and transferring a separate fluid source. 
     The first and second engagement surfaces  68 B,  70 B of the module housing  54 B each define an O-ring groove  82  having an O-ring  84  disposed therein. The O-rings  84  are adapted to seal the annular cavity  74 B and prevent leakage of the coolant  100  (shown in  FIG. 5 ). The O-rings  84  also aid in piloting and centering the module  16  into the transmission housing  72 B prior to attachment. The motor module  14  of  FIGS. 1 and 2  has structural characteristics similar to those described hereinabove for the motor module  16 . 
     Referring to  FIGS. 2 and 4 , a plurality of coolant apertures  90  in fluid communication with the annular cavity  74 A are disposed about the perimeter of the module housing  54 A. The pressurized coolant  100  (shown in  FIG. 5 ) in the annular cavity  74 A will spray out of the coolant apertures  90  at a rate defined by the amount of pressure in the annular cavity  74 A, as well as the size, shape, and number of coolant apertures  90 . According to a preferred embodiment, a first plurality of coolant apertures  90  are disposed about the perimeter of the module housing  54 A in alignment with stator windings  79 A, and a second plurality of coolant apertures  90  are disposed about the perimeter of the module housing  54 A in alignment with stator windings  81 A such that the pressurized coolant  100  is applied directly to the stator windings  79 A,  81 A to cool the motor  46 A. It should, however, be appreciated that alternate cooling aperture configurations may be envisioned. Similar cooling structure is provided on the motor module  16  of  FIG. 3 . 
     Referring to  FIGS. 4 and 5 , the coolant  100  introduced into the housing  54 A by the coolant apertures  90  accumulates until the level thereof reaches a drain  102 . The steady state level of coolant  100  in the module housing is therefore controllable by the location of the drain  102 A. It should be appreciated that in addition to the cooling of the stator windings  79 A,  81 A by the application of coolant  100  from the apertures  90 , the stator windings  79 A,  81 A are also cooled by the accumulated coolant  100  stored in the housing  54 A. 
     The housing cover  56 A is preferably piloted on and bolted to the open end  58 A of the module housing  54 A with bolts  106  so that the cover  56 A is removable if, for example, it becomes necessary to repair the motor  46 A. It should be appreciated, however, that the cover  56 A may alternatively be attached to the module housing  54 A in any conventional manner. 
     The housing cover  56 A preferably includes a plurality of mounting tabs  104  radially spaced about the cover that allow the motor module  14  to be bolted to the transmission main housing  72 A. The mounting tabs  104  provide easily accessible attachment and facilitate the absorption of stator torque by the transmission housing  72 A. The second motor module  16  of  FIGS. 1 and 3  has similar structural characteristics. 
     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.