CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 60/555,141 filed Mar. 22, 2004. 
    
    
     TECHNICAL FIELD 
     This invention relates to a transmission housing having a detachable end cover portion that selectively provides access to the components of a system without detaching the end cover portion from the main transmission housing. 
     BACKGROUND OF THE INVENTION 
     Vehicle transmissions, specifically planetary gear automatic power transmissions, typically have a park brake mechanism to resist the vehicle&#39;s natural tendency to roll down a sloped surface when the vehicle is in park. The contents of such a park brake generally include some sort of gear that is fixed with respect to the output shaft of the transmission and a pawl designed to selectively engage with the gear when the park brake is activated. The pawl substantially prevents the output shaft and attached gear from rotating when the pawl engages with the recesses between the gear teeth. 
     Vehicles with complex non-traditional powertrains, like electromechanical vehicles, still require a park brake mechanism. However, the alteration of some components in the transmission may require the park pawl and its complementary components to be altered as well. For example, some hybrid electromechanical transmissions require the use of two electric motors to supply power to the output shaft of the transmission. 
     SUMMARY OF THE INVENTION 
     The park brake may be relocated to the end portion of an electromechanical transmission to accommodate the second electric motor. Such an arrangement requires a cover to protect the park brake. The cover should be designed with a point of entry to the park brake for servicing. Therefore, the present invention provides an electromechanical transmission including a system located in a detachable end cover portion of the transmission housing. The end cover portion blankets the system while also defining an access opening that is large enough to provide access to the system without detaching the end cover portion. An access cover for the access opening is also included. 
     In one aspect of the present invention, the system is a park pawl system having a pawl, pawl return spring, and actuator guide. 
     In another aspect of the present invention, the access cover is formed of sheet metal by a stamping process. 
     In another aspect of the present invention, a controlled compression gasket is provided to further seal the access cover to the access opening. 
     In another aspect of the present invention, the end cover portion is die cast and a cast-in-place window forms the access opening. 
     More specifically, the present invention relates to a transmission including a system; a main transmission housing having a transmission opening and predetermined structural integrity; and a detachable end cover portion for substantially covering the transmission opening and configured to define a cavity for at least partially housing the system. The end cover portion has an access opening configured to enable access to the system for servicing the system without detaching the end cover portion from the transmission housing. Further included is an access cover for the access opening. Moreover, the end cover portion is configured to provide sufficient structural support to the main transmission housing when attached to the main transmission opening to maintain the predetermined structural integrity of the main transmission housing. 
     Another aspect of this invention includes a method of selectively providing access to a park pawl system located in the end cover portion of a transmission housing. The steps of the method include: providing a transmission housing with a detachable end cover portion which accommodates the park pawl system and defines an access opening configured to enable access to the park pawl system for assembly and service without detaching the end cover portion from the transmission housing; providing an access cover sufficient to cover the access opening when attached to the end cover portion of the transmission; and selectively detaching the access cover from the end cover portion to provide access to the park pawl system. 
     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 side elevational view of an electromechanical transmission housing with end cover portion and with parts broken away to show the electrical motors in their respective housings; 
         FIG. 2  is an exploded perspective view of the end cover portion, park pawl system, access opening and access cover; and 
         FIG. 3  is a perspective view of the park pawl system and relevant transmission components isolated from the main transmission housing and end cover portion. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIGS. 1 through 3 , wherein like characters represent the same or corresponding parts throughout the several views, there is shown in  FIG. 1  a schematic side elevational view of a hybrid electromechanical transmission  10 . The transmission consists of a two-part housing: the main housing  12  and the end cover portion  14 . In sum, the end cover portion  14  blankets a park pawl system  28  and defines an access opening  30  (as schematically represented in  FIG. 1 ) that is large enough to provide access to the park pawl system  28  without detaching the end cover portion  14  from the main housing  12 . An access cover  42 , as shown in  FIG. 2 , for the access opening  30  is also included. 
     More specifically, the main housing  12  contains two electric motors (A and B), which have their respective housings (or modules)  16  and  18 . Motors A and B are journaled onto the main shaft  20  of the transmission, which is selectively linked to the output shaft  22  of the transmission. The motors (A, B) operate to selectively engage with clutches (not shown) to rotate the main shaft  20  at variable speeds and indirectly rotate the output shaft  22 . Electric motor B, as shown in  FIG. 1 , fits through the opening or orifice between the main housing  12  and the end cover portion  14  at transmission opening  24  before the end cover portion  14  of the transmission is attached to the main housing  12 ; and electric motor A, as shown in  FIG. 1 , fits through the orifice or opening of the main housing  12  at  26 . The available packaging space in the main housing  12  of the transmission  10  is dominated by the drum housings ( 16  and  18 ) for the electric motors A and B, respectively (as shown in  FIG. 1 ). Therefore other transmission systems may be rearranged to accommodate. Systems relocated to the rear of the transmission, such as the park pawl system  28 , are at least partially housed by the end cover portion  14  of the transmission housing. 
     The end cover portion  14  defines an access opening  30  as shown in  FIGS. 1 and 2 . The access opening  30  is configured to provide sufficient access to the system components housed in the end cover portion  14  of the transmission as demonstrated by a hand  32  (shown in  FIG. 2 ) movable in and out of the access opening  30 . To provide access to a park pawl system  28  as shown in  FIG. 1 , the access opening  30  is approximately 41 mm in length and 120 mm in height. Lying substantially normal to the transmission opening  24 , the access opening  30  provides direct access to a pawl  34 , pawl pivot pin  36 , actuator guide  38  and pawl return spring  40  as shown in  FIG. 2 . Access to these components without detaching the end cover portion  14  from the main housing  12  is ideal for assembly and servicing. 
     To protect the system, an access cover  42  is provided as shown in  FIG. 2 . The access cover  42  is large enough to cover the access opening  30 . In the preferred embodiment, the access cover  42  is approximately 60 mm in length and 137 mm in height. The access cover  42  is mounted onto the end cover portion  14  by structural connectors  44 . In the preferred embodiment, the access cover  42  is composed of a steel alloy and formed by stamping processes. 
     A controlled compression gasket  46  is provided between the access opening  30  and the access cover  42  to substantially prevent the leakage of any oil outside the end cover portion  14  and to prevent unwanted debris from entering the end cover portion  14 . In the preferred embodiment, the controlled compression gasket  46  is hollowed to match the access opening  30  of the end cover portion  14 . The controlled compression gasket  46  is composed of elastomer material, ethelene acrylic or a reasonable substitute, and molded over a mold support made of steel sheet metal. The steel support is additionally provided with ferritic compression limiting washers  50  defining complementary holes to accept the structural connectors  44  of the access cover  42 . The elastomer material is molded in a fashion to conform under the compressive load provided by the connectors  44 , forming a seal to both the end cover portion  14  and the access cover  42 , which prevents any leakage of oil outside of the assembly and prevents introduction of debris into the assembly. The degree of conformance of the elastomer material under compressive load by the connectors  44  is controlled by the compression limiting washers  50 . The elastomer material of the controlled compression gasket  46  and the compression limiting washers  50  are held in their desired shape and by the mold support. 
     The end cover portion  14  also provides structural support to the main housing  12  of the transmission  10  (shown in  FIG. 1 ). The access opening  30  is small enough and appropriately placed so that the end cover portion  14  maintains the maximum structural integrity needed for the end cover portion  14  to function as a structural component for the main housing  12 . The main housing  12  and end cover portion  14  see torsional loading from the repetitive revolutions of the electric motors (A and B), engine (not shown), clutches (not shown), and output shaft  22 . The end cover portion  14  is configured to withstand the torsional loads, driveline loads, clutch piston loads, and park pawl loads of a 7800 pound vehicle, thereby providing sufficient structural support to the main housing  12  to preserve its structural integrity. To provide this support, the end cover portion  14  is designed to be a uniform structure, as better seen in  FIG. 2 , and is comprised of an enhanced aluminum alloy die casting Grade ANSI A380.0 or Grade ANSI 383.0. The uniform structure of the end cover portion  14  and use of this alloy provides the necessary structural support while also reducing the weight and material costs of the transmission  10 . 
     Though the end cover portion  14  may be manufactured through a number of processes, in the preferred embodiment the end cover portion  14  is manufactured by die-casting. Generally, die-casting is compatible with the use of aluminum alloys. Additionally, die-casting generally also provides excellent dimensional accuracy and stability in high volume manufacturing. The end cover portion  14  has a complex geometry, as shown in  FIG. 2 , wherein die-casting configures contours to facilitate the park pawl system  28  and its complimentary components—shown in FIG.  2 —while remaining compact enough to meet the aforementioned compact packaging requirements. The die (not shown) for the end cover portion  14  is designed with configurations to provide such contoured surfaces. 
     Finally,  FIG. 3  details the park pawl system  28 . An engagement gear  52  has a number of teeth  54  and tooth recesses  56  on its perimeter. On the inner diameter of the engagement gear  52  are a series of complementary splines  58  functioning to secure the engagement gear  52  directly onto a clutch housing  60  (as shown in  FIG. 2 ) and indirectly onto the output shaft  22  (shown in  FIG. 1 ). When the wheels of the vehicle rotate by external forces, such as gravity, the drive shaft also turns and causes the output shaft  22  and engagement gear  52  on the clutch housing  60  to rotate as the engagement gear  52  is configured to rotate with the output shaft  22 . 
     With reference to  FIG. 3 , the park pawl system  28  consists of a pawl pin  36 , torsion spring (or pawl return spring  40 ), pawl  34  and actuator guide  38 . The pawl  34 , actuator  62 , and actuator guide  38  are placed in the end cover portion  14 , situated to axially align the pawl  34  with the pawl engagement gear  52 . The pawl  34  is configured to fit in the tooth recesses  56  on the engagement gear  52  perimeter upon activation of the park pawl system  28  (as shown at  64 ). The pawl  34  is mounted on the pawl pin  36 , and is free to rotate or pivot about the pawl pin  36 . A pawl return spring  40  operates to hold the pawl  34  in the disengaged position except when mechanically engaged. The pawl  34  is mounted adjacent to a slotted actuator guide  38  and actuator  62  so that upon transverse motion of the actuator  62  the pawl  34  is rotated or pivoted between the engaged and disengaged positions. 
     The actuator guide  38  encases the actuator  62  and is secured by a pin  66  (through aperture  68  shown in  FIG. 2 ) with respect to the end cover portion  14 . The end cover portion  14  is hollowed at pocket  70  to receive and accommodate the end shape of the actuator guide  38 . Movement of the actuator  62  aft causes the cam portion  72  and wide portion  74  of the actuator  38 , shown in  FIG. 3 , to collide with the back  76  of the pawl  34  and force the pawl  34  to rotate or pivot into engagement with a tooth recess  56  in the engagement gear  52 . Movement of the actuator  62  forward with respect to the pawl  34  moves the cam portion  72  away from the back  76  of the pawl  34  to remove the force of the cam, whereby to release the pawl  34  from the tooth recess  56 . When the pawl  34  is released from the tooth recesses  56 , the pawl return spring  40  rotates the pawl  34  into the disengaged position allowing the engagement gear  52  to freely rotate. 
     The actuator  62  is spring mounted to an end portion  78  of the connecting rod  80 . The axially positioned linear spring (or actuator return spring  82 ) functions to enable shift selection of park regardless of the position of pawl  34  relative to the engagement gear  52 , teeth  54  and tooth recesses  56 . With reference to  FIGS. 1 and 3  the connecting rod  80  is secured to the detent lever  84  of the shift selector  85  at  86 . The detent lever  84  is pivotably secured with respect to the main housing  12  of the transmission at  88 , where the selector shaft lever (not shown) is also connected. The perimeter of the detent lever  84  has detents  90  on its lower end. The detents  90  are configured to engage with the cylindrical end  92  of a detent retention spring  94 . The detent retention spring  94  is indirectly mounted with respect to the main housing  12  of the transmission so that upon placing the vehicle in park the selector shaft lever rotates the detent lever  84  and the cylindrical end  92  of the detent retention spring  94  engages with the most aft detent  96  of the detent lever  84  to secure it in place. To reach this position the detent lever  84  rotates clockwise, or rearward with respect to the main housing  12  moving the connecting rod  80  rearward or toward the end cover portion  14  of the transmission  10 . 
     The access opening  30 , as shown in  FIGS. 1 and 2 , is designed to provide access to the rear mounted components of the park pawl system ( 34 ,  36 ,  38  and  40 ) as detailed above. 
     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.
This invention relates to the housing of a hybrid electro-mechanical transmission consisting of park pawl system located in the end cover portion of the transmission housing. The end cover portion is configured to cover the park pawl system and allow access to the components of the park pawl system for assembly or service even as the end cover portion remains attached to the main housing of the transmission. An access cover and seal for the access opening in the end cover portion is also provided. The access opening is designed to be small enough so that the end cover portion can also provides structural support to a main housing portion during operation of the transmission. A method of selectively providing access to a park pawl system located in the end cover portion of a transmission housing is also provided.