Abstract:
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. Beyond providing coverage to the park pawl system, the end cover portion also provides structural support to a main housing portion during operation of the transmission. A method of assembling a park pawl system between main and end cover portions of a transmission housing is also provided.

Description:
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 hybrid electro-mechanical transmission having a park pawl system, which is at least partially located and assembled in an end cover portion of a 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. One example of a successful park pawl arrangement is described in commonly assigned U.S. Pat. No. 5,630,339 entitled “Park Mechanism for Vehicle Transmission,” Tuday, T May 20, 1997, and hereby incorporated by reference in its entirety. 
     Vehicles with complex non-traditional powertrains, like electro-mechanical vehicles, still require a park brake mechanism. However, the alteration of some components of the transmission may require the park pawl and its complementary components to be altered as well. For example, some hybrid electro-mechanical transmissions require the use of two electric motors to supply power to the output shaft of the transmission. The two motors significantly increase the amount of packaging space needed for the transmission. Therefore, the surrounding transmission components, including the park brake mechanism, must be adjusted to accommodate the additional power supply. The location and placement of these surrounding components, however, is limited by the dimensions of neighboring vehicle components and by any clearance requirements for the underbody of the vehicle. The park pawl for the aforementioned transmission was placed farther rearward to accommodate the second electric motor. A cover or housing was required to protect the park brake from contamination. Major design considerations of the rear cover include manufacturability, structural integrity, weight, and material costs requirements. 
     SUMMARY OF THE INVENTION 
     In light of the design challenges mentioned, the present invention provides a transmission housing with a park pawl system located in an end cover portion of the transmission housing. The end cover portion blankets the park pawl system while also defining a cavity that is large enough to provide access to the park pawl system through the exterior of the end cover portion. 
     In one aspect of the present invention, the end cover portion is detachable from the main housing of the transmission. However, the park pawl system remains accessible without detaching the end cover portion from the main housing. 
     In another aspect of the present invention, a shift selector located in the main housing of the transmission is mechanically linked to the park pawl system in the end cover portion of the transmission. The end cover portion has an aperture through which a connecting rod extends between the shift selector and park pawl system. 
     In another aspect of the present invention, an aperture is included in the end cover portion to allow for the installation of a pawl pin onto the pawl without detaching the end cover portion from the main housing of the transmission. 
     In an additional aspect of the present invention, the end cover portion is designed to be sufficiently strong enough to provide structural support to the main housing of the transmission during operation. 
     More specifically, the present invention relates to a transmission including a transmission housing, with a main housing which defines a portion of the transmission housing and a park pawl system which is at least partially located in an end cover portion of the transmission housing. 
     Another aspect of this invention is a method of assembling a hybrid electro-mechanical vehicular transmission having an electric motor module and a park pawl engagement system. The method includes providing a transmission main housing with a terminal portion sufficiently open-ended to receive and house the electric motor module and a first portion of the park pawl engagement system; providing a transmission end cover sufficiently expansive for covering the open-end of the terminal portion and sufficiently configured to house a second portion of the park pawl engagement system; assembling the first portion of the park pawl engagement system in the transmission main housing; assembling the second portion of the park pawl engagement system in the transmission end cover; and mechanically interconnecting the first and second portions of the park pawl engagement system during the covering of the open-end of the terminal portion by the transmission end cover. 
     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 electro-mechanical transmission housing with end cover portion and with parts broken away to show the electrical motors in their respective housings; 
         FIG. 2  is a perspective view of the engagement gear, park pawl system, connecting rod, and shift selector isolated from the main transmission housing and end cover portion; and 
         FIG. 3  is an exploded perspective view of the end cover portion, engagement gear, park pawl system, and access cover. 
     
    
    
     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 electro-mechanical transmission  10 . The transmission consists of a two-part housing: the main housing  12  and the end cover portion  14 . 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 . 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 ). One technical advantage of the present invention is that it enables the main housing  12  to accommodate both electric motors (A and B) by rearranging the position of other transmission components, namely the park pawl system  28 . Located between and encircled by the pair of motors is a shift selector  24  that is connected (either mechanically or electrically) to the transmission gear shifter (not shown) and to a mechanical link (or connecting rod  26 ) that controls the park pawl system  28 . The park pawl system  28  is encased by the end cover portion  14  of the transmission housing and functions to selectively interact with an engagement gear  30 , which is secured to rotate with the output shaft  22 . The end cover portion  14  defines a cavity  31 , which provides sufficient access to the park pawl system  28  and its components for assembly and servicing without detaching the end cover portion  14  from the main housing  12 . 
       FIG. 2  details the interaction between the engagement gear  30 , park pawl system  28  and the shift selector  24 . The engagement gear  30  has a number of teeth  32  and tooth recesses  34  on its perimeter. On the inner diameter of the engagement gear  30  are a series of complementary splines  36  functioning to secure the engagement gear  30  directly onto the clutch housing  72  (as shown in  FIG. 3 ) 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  30  on the clutch housing  72  to rotate as the engagement gear  30  is configured to rotate with the output shaft  22 . 
     With reference to  FIG. 2 , the park pawl system  28  consists of a pawl pin  38 , torsion spring (or pawl return spring  40 ), pawl  42  and actuator guide  46 . The pawl  42 , actuator  48 , and actuator guide  46  are placed in the end cover portion  14 , situated to axially align the pawl  42  with the pawl engagement gear  30 . The pawl  42  is configured to fit in the tooth recesses  34  on the engagement gear  30  perimeter upon activation of the park pawl system  28  (as shown at  35 ). The pawl  42  is mounted on the pawl pin  38 , and is free to rotate or pivot about the pawl pin  38 . A pawl return spring  40  operates to hold the pawl  42  in the disengaged position except when mechanically engaged. The pawl  42  is mounted adjacent to a slotted actuator guide  46  and actuator  48  so that upon transverse motion of the actuator  48  the pawl  42  is rotated or pivoted between the engaged and disengaged positions. 
     The actuator guide  46  encases the actuator  48  and is secured by a pin  76  (through aperture  77  shown in  FIG. 3 ) with respect to the end cover portion  14 . The end cover portion  14  is hollowed at pocket  75  to receive and accommodate the end shape of the actuator guide  46 . The actuator guide  46  has an inner cavity  54  contoured to the shape of the actuator  48  (as shown in  FIG. 2 ). The actuator guide  46  has a slot  50  on its perimeter, adjacent the back  43  of the pawl  42 , which is configured to guide and support the pivotal movement of the pawl  42 . Movement of the actuator  48  aft causes the cam portion  49  and wide portion  52  of the actuator to collide with the back  43  of the pawl and force the park pawl  42  to rotate or pivot into engagement with a recess  34  in the engagement gear  30 . Movement of the actuator  48  forward with respect to the pawl  42  moves the cam portion  49  away from the back  43  of the pawl  42  to remove the force of the cam, whereby to release the pawl  42  from the tooth recess  34 . When the pawl  42  is released from the tooth recesses  34 , the pawl return spring  40  rotates the pawl  42  into the disengaged position allowing the engagement gear  30  to freely rotate. 
     The actuator  48  is spring mounted to an end portion  27  of the connecting rod  26 . The axially positioned linear spring (or actuator return spring  58 ) functions to enable shift selection of park regardless of the position of pawl  42  relative to the engagement gear  30 , teeth  32  and tooth recesses  34 . If an engagement gear tooth  32  is located over or adjacent to the pawl  42  when park is selected, the pawl will not engage in a recess  34 , but the end  27  of the connecting rod will continue to move with respect to the actuator  48  against the bias of spring  58 , and the end  27  of the connecting rod will extend slightly beyond the end  55  of the actuator. The actuator return spring  58  enables selection of park by maintaining an axial force or bias on the actuator  48  until the engagement gear  30  rotates to a point where the gear tooth  32  is no longer adjacent to the pawl  42 . With the continued bias of actuator return spring  58 , the pawl  42  will then engage with a tooth recess  34  at the first opportunity (usually when the vehicle starts or continues to roll). The end  27  of the connecting rod  26 , which functions as a mechanical link between the shift selector  24  and the actuator  48  then moves again with respect to the actuator  48  as the pawl  42  engages the tooth recess  34 . 
     With reference to  FIGS. 1 and 2 , the connecting rod  26  is secured to the detent lever  60  of the shift selector at  61 . The detent lever  60  is pivotably secured with respect to the main housing  12  of the transmission at  62 , where the selector shaft lever (not shown) is also connected. The perimeter of the detent lever  60  has detents  64  on its lower end. The detents  64  are configured to engage with the cylindrical end  66  of a detent retention spring  68 . The detent retention spring  68  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  60  and the cylindrical end  66  of the detent retention spring  68  engages with the most aft detent  70  of the detent lever  60  to secure it in place. To reach this position the detent lever  60  rotates clockwise, or rearward with respect to the main housing  12  moving the connecting rod  26  rearward or toward the end cover portion  14  of the transmission housing  10 . 
     Though this is the configuration of the park pawl system  28  in the preferred embodiment, the invention is also compatible with a variety of park systems such as the one described in U.S. Pat. No. 5,685,406 entitled “Park Brake Actuating Mechanism For A Power Transmission,” Crum, et al., Nov. 11, 1997, assigned to General Motors Corporation and hereby incorporated by reference in its entirety. 
     The end cover portion  14  of the transmission housing, as shown in  FIG. 3 , is designed to encase the engagement gear  30  and park pawl system ( 38 ,  40 ,  42 ,  46  and  50 ). The end cover portion  14  is hollowed large enough at  31  to encase the engagement gear  30  and allow it to freely rotate. Splined to the engagement gear  30  is a clutch housing  72 , which is also drivably connected to the output shaft  22  (only shown in  FIG. 1 ) of the transmission. The end cover portion  14  contains an aperture  15  to allow for the output shaft  22  to extend out of the end cover portion  14  of the transmission housing. The end cover portion  14 , as shown in  FIG. 3 , defines a cylindrical cavity  31  configured at one side to encircle and support the actuator guide  46  respectively at a pocket  75  and a formed cavity portion  74 . The actuator guide  46  is secured to the end cover portion  14  by a pin  76  that runs through the end cover portion  14  at  78  and actuator guide  46  at  77 . The end cover portion  14  allows for the connecting rod  26  of the shift selector  24  (both shown in  FIG. 2 ) to pass from the main housing  12  of the transmission to the actuator  48  in the actuator guide  46  in the end cover  14  without interference. In addition to housing the park pawl system  28  and its components, the end cover portion  14  also defines several orifices ( 80 ,  82 ), which provide access to the park pawl system from the outside of the transmission. The first orifice  80  defines an access opening for assembly and service of the park pawl system  28 . Orifice  82  provides an entry point for the pawl pin  38  to be assembled to the pawl  42  on the end cover portion  14 . The end cover portion  14  further contains a compression gasket  84  to seal the end cover portion  14  as well as a detachable access cover  86  to close the end cover portion  14  of the transmission. The compression gasket  84  and access cover  86  are attached to the end cover portion  14  by a series of structural connectors (or bolts)  88 . The end cover portion  14  is attachable to the main housing  12  by similar structural connectors such as  88  at mating orifices such as  90 . 
     In sum, the connecting rod  26  between the shift selector  24  and the park pawl engagement system  28  passes through cast openings  94  in the transmission housing  12  and rear cover  14 . The connecting rod  26 , actuator  48 , and actuator return spring  58  are assembled with the transmission main housing  12 . The pawl engagement gear  30 , pawl  42 , pawl return spring  40 , and actuator guide  46  are assembled with the transmission rear cover  14 . The actuator  48 , actuator return spring  58 , and connecting rod  26  are passed thru the transmission main housing  12  and rear cover cast windows or configurations  74 , and funneled into the actuator guide  46  during final assembly of the transmission  10 . 
     The end cover portion  14  also provides structural support to the main housing  12  of the transmission  10  (shown in  FIG. 1 ). The main housing  12  and end 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 lb. vehicle. To provide this support the end cover portion  14  is designed to be a uniform structure, as better seen in  FIG. 3 , and 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. 
     In addition to structural support and reinforcements, the end cover portion  14  is designed to comply with packaging constraints and simplify assembly requirements. Primarily, the assembled transmission housing  10  must be compact enough on the inside to contain the park pawl system  28  without impinging upon neighboring vehicle components  98  while still providing the necessary underbody clearance for the vehicle. Additionally, various components located in the main housing  12  of the transmission  10  are accessible from both or either ends  94  or  96  of the main housing  12 . Namely, electric motor B, as shown in  FIG. 1 , should fit through the opening or orifice between the main housing  12  and the end cover portion  14  at  94  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 , should fit through the orifice or opening of the main housing  12  at  96 . The main housing  12  and end cover portion  14  may be designed to provide various other points of entry into the transmission to simplify the assembly of the components located in the main housing  12 , including a main housing  12  which can be accessed through either side of the main housing. 
     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 involving high volumes. The end cover portion  14  has a complex geometry, as shown in  FIG. 3 , 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. 
     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.