Abstract:
A clutch assembly for a vehicle transmission includes a housing defined by a wall having an annular configuration circumscribing a clutch axis. The wall extends between an open end and a floor. The floor extends inwardly from the wall toward the clutch axis. A plurality of splines formed in the wall and each is spaced from the open end of the housing. A snap ring retains clutch plates in the housing. The open end of the wall is deformed inwardly toward the clutch axis defining a retainer for retaining the snap ring within the housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally toward a clutch for use in an automotive transmission. More specifically, the present invention relates toward an improved clutch housing and retention assembly. 
         [0002]    Clutches are known to be used in an automatic transmission assembled to a power train of a vehicle. An increased number of clutches assembled into a transmission are also known to improve mileage performance of a vehicle. For example, a transmission having only four clutches does not perform as well, or provide as good mileage performance, as a transmission having six, or even eight clutches. Due to the increasing cost of fuel, most vehicle companies are engineering new transmissions having eight and even nine clutches. 
         [0003]    A typical clutch includes an annular housing having an annular wall defining a plurality of spaced splines. These splines are typically formed by a process known as “lance-and-form” to provide a gear-like interface with a plurality of clutch plates retained inside the clutch housing. Occasionally, the splines are formed in the annular wall by machining a substantially thicker housing when additional structural integrity is required. Inside the clutch housing, a piston is retained adjacent a base of the housing and circumscribes a transmission shaft through which oil flows in between the housing base and the piston. The piston is separated from the plurality of clutch plates by a steel spacer. 
         [0004]    The splines that are defined by the annular wall of the housing extend to the distal end of the housing. A snap ring groove is formed into the splines by either a machining or a reverse lance-and-form process. A snap ring is inserted into the groove to retain the clutch components set forth above. Clutches typically fail because the weakness of the reverse lance-and-formed groove formed into the splines of the clutch housing. Sharp edges defined by the reverse lance create weaknesses in the housing that are known to crack, particularly when the transmissions are under heavy load. Attempts have been made to improve the integrity of the snap ring groove and the clutch housing by increasing the thickness of the clutch housing and extending the distance between the snap ring groove and the open end of the housing. None of these attempts to improve the integrity of the housing have proven sufficient. Furthermore, increasing the thickness of the housing adds weight to the vehicle transmission, particularly given eight clutches are becoming more prevalent in some transmissions. Furthermore, extending the distance between the snap ring groove and the end of the clutch housing makes use of packaging space unnecessarily causing increase inside a transmission. Therefore, there is a strong need to redesign the clutch and the clutch housing to reduce mass, increase structural integrity, particularly to retain the snap ring, and reduce the amount of packaging space required for a given clutch. 
       SUMMARY OF THE INVENTION 
       [0005]    A clutch assembly for a transmission, particularly for a vehicle transmission, includes a housing defined by a wall having an annular configuration circumscribing a clutch axis. The wall extends between an open end and a floor and the floor extends inwardly from the wall toward the clutch axis. A plurality of splines is formed in the wall and the splines are spaced from the open end of the housing. The snap ring retains a plurality of clutch plates and fibrous plates in the clutch housing. The open end of the wall is deformed inwardly toward the clutch axis at the open end of the housing defining a retainer for retaining the snap ring within the housing. 
         [0006]    The inventive clutch and clutch housing eliminates the lance-and-form snap ring groove known to prior art clutch housings, which typically causes failure in an automotive transmission. The retainer of the present clutch housing is defined by deforming an annular wall of the housing radially inwardly to define the retainer between the upper end of the splines and the deform wall. In effect, the snap ring retention is achieved by “hemming” the top of the housing and results in a full 360° retention. This configuration of the snap ring retainer eliminates the weaknesses associated with the prior art lance-and-formed snap ring groove that are caused from forming a reverse lance cut in the plurality of splines formed in the clutch housing. This lance cut causes a stress rising condition resulting a release of the snap ring from the clutch housing. It is believed that the thickness of the clutch housing can now be reduced by upwards of 0.5 millimeters providing a 20% decrease in the mass of a typical housing. Furthermore, the splines no longer extend to the open end of the clutch housing, but are spaced from the open end of the housing to facilitate the deformation of the open end to form the retainer from the snap ring. This facilitates a reduction of the axial length of the clutch housing reducing the packaging space required of each clutch of the automotive transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in light of accompanying drawings in which: 
           [0008]      FIG. 1  shows a cross-sectional view of the clutch of the present invention; 
           [0009]      FIG. 2  shows a fragmented, perspective view of the clutch housing of  FIG. 1 ; 
           [0010]      FIG. 3  shows a plan view of the clutch housing of the present invention; 
           [0011]      FIG. 4  is a sectional view of line  4 - 4  of  FIG. 3  showing an installation of an individual clutch plate; 
           [0012]      FIG. 5  is a sectional view of line  5 - 5  of  FIG. 3  showing an installation of an individual clutch plate; 
           [0013]      FIG. 6  shows a partial plan view of a clutch plate; 
           [0014]      FIG. 7  shows a partial plan view of the inventive clutch assembly having a clutch plate installed; 
           [0015]      FIG. 8  shows a partial plan view of a clutch assembly having a clutch plate and a retention or snap ring installed; 
           [0016]      FIGS. 9 and 10  shows a sectional view of the retainer and retainer teeth with the snap ring installed; 
           [0017]      FIG. 11  shows a partial perspective view of the clutch housing prior to forming the retainer; 
           [0018]      FIG. 12  shows a partial sectional view of the clutch housing prior to forming the retainer; 
           [0019]      FIG. 13  shows a partial perspective view of the clutch housing having retention teeth formed prior to forming the retainer; 
           [0020]      FIG. 14  shows a partial perspective view of an alternative clutch housing of the present invention; and 
           [0021]      FIG. 15  shows a partial sectional view having a retainer ring and clutch plates installed into the alternative clutch housing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring to  FIG. 1 , a side sectional view of the clutch assembly of the present invention is generally shown at  10 . The assembly  10  includes a housing  12  defined by an annular wall  14 . The annular wall  14  circumscribes a transmission shaft  16  that defines a shaft axis A. The annular wall  14  of the housing  12  extends axially between an open end  18  and a floor  20 . The floor  20  extends radially inwardly toward the transmission shaft  16 . A piston  22  circumscribes the transmission shaft  16  and is positioned adjacent the floor  20  of the housing  12 . A seal  23  seals the floor  20  of the housing  12  to the transmission shaft  16 . Transmission fluid pumps through the transmission shaft  16  through outlets  24  and to the space located between the piston  22  and the floor  20  of the housing  12  to shift the clutch assembly  10  in a known manner. A fibrous plate  28  circumscribes the transmission shaft  16  and is positioned in an abutting relationship between the piston  22  and a plurality of clutch plates  26 . The clutch plates  26  are separated by fibrous plates  28 . Clutch plates  26  and the fibrous plates  28  circumscribe the transmission shaft  16  and are retained in the housing  12  by snap ring  30  as will be explained further herein below. A clutch pressure plate  32  is disposed between the plurality of clutch plates  26 , the fibrous plates  28 , and the snap ring  30 . A shift member  34  overlies the open end  18  of the housing  12  and provides biasing support to biasing member  36  for biasing the piston  22  toward the floor  20  of the housing  12 . 
         [0023]    The housing  12  defines a plurality of housing splines  38  spaced around a full 360° of the housing  12  as best shown in  FIG. 2 . The shift member  34  defines a plurality of member splines  40  as seen in  FIG. 1  so that the housing splines  38  and the member splines  40  are opposed enabling positioning of the clutch plates  26  engage either the housing splines  38  or the member splines  40  as shown in  FIG. 1 . Therefore, it should be understood by those of ordinary skill in the art that the clutch plates  26  define a plurality of spaced teeth  42  that engage the housing splines  38  in a gear-like manner. The teeth  42  of the clutch plates  26  are best represented in  FIG. 6 . 
         [0024]    Referring now to  FIG. 2 , a retainer  44  is positioned at the open end  18  of the housing  12 . The retainer  44  extends radially inwardly toward the transmission axis A and defines a plurality of retainer teeth  46 . Each of the retainer teeth  46  is circumferentially aligned with one of the plurality of housing splines  38 , the purpose of which will be explained further below. Each of the housing splines  38  are spaced from the open end  18  of the housing  12  so that a space  48  is defined between the retainer  44  and the housing splines  38 . As shown in  FIG. 1 , a snap ring  30  is located in space  48  defined between the retainer  44  and the housing splines  38 . Referring again to  FIG. 2 , the housing splines  38  are also spaced from the floor  20  of the housing  12 . Although the housing splines  38  are represented as an inwardly projecting deformation in the annular wall  14  of the housing  12 , it should be understood to those of ordinary skill in the art that the housing splines  38  may be formed by a cold formed process. 
         [0025]    Referring now to  FIGS. 3-5 , the plurality of housing splines  38  define a minor housing diameter  50  of the housing  12  and the annular wall  14  of the housing  12  defines a major housing diameter  52 . Likewise, the retainer  44  defines a major retainer diameter  54  between each of the retainer teeth  46  and a minor retainer diameter  56  defined by the radially inwardly-most portion of the retainer teeth  46 . It is contemplated by the inventor that the major retainer diameter  54  includes a length that is between the minor housing diameter  50  and the major housing diameter  52 . However, it is necessary that the major retainer diameter  54  is greater than the outer-most diameter of the teeth  42  on the clutch plates  26 . Further, the minor retainer diameter  56  is contemplated to be proximate the minor housing diameter  50 . However, the minor retainer diameter  56  should be no less than a minor diameter of the clutch plates  26 . 
         [0026]    The diameters as set forth above of the various elements of the housing  12 , the retainer  44 , and the retainer teeth  46  facilitate the installation of the clutch plates  26  into the housing  12 . 
         [0027]      FIG. 7  shows a partially assembled clutch assembly  10  where a clutch plate  26  is shown being received by the housing splines  38  and the retainer teeth  46 . The clutch plate teeth  42  are shown spaced from the major housing diameter  52 . It should be understood by those of ordinary skill in the art that the clutch plate teeth  42  need merely be receivable by the retainer  44  and be engagable with the housing splines  38  to be fully operable. 
         [0028]      FIG. 8  shows another view of a partially assembled clutch assembly  10  having the snap ring  30  retained by the retainer  44  and being positioned in the space  48  between the housing splines  38  and the retainer  44 . 
         [0029]    Referring to  FIGS. 9 and 10 , the snap ring  30  is shown positioned in the space  48  defined between the retainer  44  and the housing splines  38 . It should be apparent by  FIG. 10  that the snap ring  30  achieves 360° of contact and retention by the retainer  44 . As set forth above, prior art snap ring grooves have only provided 180° of partial contact to the snap ring resulting in localized stresses developing on the prior art housing causing known failures. Additional structural integrity is shown in  FIG. 9  where the retainer teeth  46  provide 180 degrees of further contact and retention to the snap ring  30 . It is believed that a 20% reduction in the thickness of the sheet metal used to form the housing  12  is achievable by virtue of the increased contact between the retainer  44  and the snap ring  30  versus the current lance-and-form snap ring groove design. 
         [0030]    The method of forming the retainer will now be explained. Referring to  FIG. 11 , a partial cross-sectional view of the housing  12  is shown prior to formation of the retainer  44 . Therefore, one of the plurality of housing splines  38  is shown having a diameter less than an upper flange  58  of the partially formed housing  12 . It is obvious to one of ordinary skill in the art that the housing splines  38  are clearly spaced from an open end of the housing  12 , even prior to full formation of the retainer  44 . A fragmented line  6  shows the target hem of the flange  58  to define the retainer  44 , and therefore the space  48 , disposed between the retainer  44  and the plurality of housing splines  38 . It should be noted that hem material thickness is constant of the parent incoming material thickness used on the entire clutch housing. However, prior to forming the housing flange  58 , the housing flange  58  is slotted to define the retainer teeth  46 , as best represented in  FIG. 13 . Once the retainer teeth  46  have been slotted into the flange, the retainer  44  is formed by a rolling or flow forming a process to define the space  48  disposed between the retainer  44  and the housing splines  38  as seen in  FIGS. 9 and 10 . It should be further understood by those of skill in the art, that the space  48  defined between the retainer  44  and the housing splines  38  is constant, while the snap ring  30  is selected from a plurality of thicknesses to accommodate assembling a variation of the clutch assembly  10 . Therefore, it is believed the snap ring  30  will have some float within the space  48  defined by the retainer  44  and the housing splines  38  dependent upon the thickness of the snap ring  30  selected at the time of assembly. 
         [0031]    An alternative retainer  60  is represented in  FIGS. 14 and 15 . Elements that are the same as those disclosed in the prior embodiment include the same element numbers. The alternative retainer  60  defines an outer retainer wall  62  having a diameter greater than the major housing diameter  52 . In this embodiment, the alternative retainer  60  does not include retainer teeth, but provides a more extensive overlap with the snap ring  30 , as is best represented in  FIG. 15 . In this embodiment, additional contact with the snap ring  30  is made by the retainer so that 360° of contact is achieved with a more substantial portion of the alternative retainer  60  by way of alternative retainer lip  64 . As further represented in  FIG. 15 , snap ring  30  includes an outer diameter that is greater than the major housing diameter  52 . However, snap ring  30  provides sufficient overlap with the pressure plate  32 , the clutch plates  26 , and the fibrous plates  28  to adequately retain the clutch assembly  10 . 
         [0032]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation while material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.