Abstract:
Components for an automatic motor vehicle transmission including a band brake drum, a clutch housing or hub having a seal surface or a clutch housing or hub utilized in a friction clutch assembly having a spline set. All of these components are fabricated of aluminum and the outer surface of the band brake drum, the housing or hub sealing surface and the area of the spline set includes a thin coating of a thermally sprayed steel material. The thermally sprayed steel material may be a low carbon steel such as SAE 1008 or 1010, a similar alloy, iron or other metal. The resulting components thus exhibit the weight saving of aluminum while providing excellent service life due to the enhanced strength and wear resistance provided by the thermally sprayed steel coating.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/012,041, filed Jun. 13, 2014, which is hereby incorporated in its entirety herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to aluminum components for automatic transmissions and more particularly to an aluminum band brake drum, a clutch hub seal area, a bushing area and a clutch hub spline area having a thin layer of steel, iron or similar metal disposed thereon. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0004]    A conventional automatic transmission may include one or more band brakes, friction clutch assemblies and planetary gear assemblies. A band brake includes a band drum coupled to a rotating component such as an element of a planetary gear assembly and surrounded by a brake band that may be tightened about the drum by an actuator to brake the drum and associated component. A friction clutch includes pluralities of interleaved friction plates and reaction plates disposed between an inner hub with which the friction plates rotate and an outer housing with which the reaction plates rotate. Between the clutch hub or housing and other components such as shafts, quills or planetary gear components, it is often necessary to establish a fluid tight seal in order to either separate fluid filled, i.e., wet, areas from dry areas or to establish a flow path for fluid across or between rotating and non-rotating components. This may be achieved by, in the first case, a resilient seal disposed in a channel or groove between the areas or, in the second case, utilizing a pair of resilient seals disposed in grooves on both sides of the flow path to properly direct fluid flow. Also, one or both of the inner hub and outer housing may be coupled to a shaft or quill by splines. 
         [0005]    Conventionally, band brake drums, friction clutch hubs and housings and components having surfaces engaged by resilient seals or including splines have been fabricated of various steels due to the strength and durability these materials provide. 
         [0006]    While various steels provide the necessary strength and durability, they are not without drawbacks. The primary contemporary issue with such steel components is weight. Since these components are both carried and translated as part of the total vehicle weight and rotate and thus contribute to powertrain energy loss as they are repeatedly accelerated, they twice contribute to fuel consumption. Accordingly, any weight reduction of a rotating component, such as a brake drum, clutch housing or hub, positively affects fuel consumption both from the standpoint of total vehicle weight as well as powertrain efficiency. 
         [0007]    A solution to the weight problem is the substitution of a lighter weight material such as aluminum. Aluminum has about one-third the density of steel and exhibits good heat transfer, both characteristics being important and beneficial in transmission applications. However, it has been found that a aluminum band brake drum, an aluminum clutch housing or hub or an aluminum component having splines or a sealing surface is unsuitable because aluminum does not exhibit suitable wear resistance for use as a brake drum, it may not have sufficient strength to transfer torque across a splined interconnection in a transmission and wear resistance in a bushing surface or seal application is also problematic. 
         [0008]    Thus, while aluminum is an attractive from weight and energy savings standpoints, due to its limited strength, especially relative to common steels, in applications involving frictional service and relatively high torque levels, aluminum remains an unattractive alternative. The present invention addresses these shortcomings. 
       SUMMARY 
       [0009]    The present invention provides components for an automatic transmission including a band brake drum, a clutch housing or hub having a bushing interface surface or a seal surface or a clutch housing or hub utilized in a friction clutch assembly having a spline set. All of these components are fabricated of aluminum and the outer (friction) surface of the band brake drum, the housing or hub seal or bushing surface or surfaces and the spline set and adjacent area includes a thin coating of a thermally sprayed steel material. The thermally sprayed steel material may be a low carbon steel such as SAE 1008 or 1010, a similar alloy, iron or other metal. The resulting components thus exhibit the weight saving of aluminum while providing excellent service life due to the enhanced strength and wear resistance provided by the thermally sprayed steel coating. 
         [0010]    It is thus an aspect of the present invention to provide an automatic transmission component fabricated of aluminum and having a thin layer of thermally sprayed steel material. 
         [0011]    It is a further aspect of the present invention to provide a brake drum for a friction drum brake assembly fabricated of aluminum and having a thin layer of thermally sprayed steel material on its outer surface. 
         [0012]    It is a still further aspect of the present invention to provide a component for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed steel material on a seal surface or surfaces. 
         [0013]    It is a still further aspect of the present invention to provide a component for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed steel material on a bushing interface surface or surfaces. 
         [0014]    It is a still further aspect of the present invention to provide a housing or hub for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed steel material on a spline set. 
         [0015]    It is a still further aspect of the present invention to provide a brake drum for a friction drum brake assembly fabricated of aluminum and having a thin layer of thermally sprayed SAE 1008 or 1010 steel, iron or other material on its outer surface. 
         [0016]    It is a still further aspect of the present invention to provide a component for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed SAE 1008 or 1010 steel, iron or other material on a seal surface or surfaces. 
         [0017]    It is a still further aspect of the present invention to provide a component for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed SAE 1008 or 1010 steel, iron or other material on a bushing interface surface or surfaces. 
         [0018]    It is a still further aspect of the present invention to provide a unitary housing or hub for a friction clutch assembly fabricated of aluminum and having a thin layer of thermally sprayed SAE 1008 or 1010 steel, iron or other material disposed on a spline set. 
         [0019]    Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0020]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0021]      FIG. 1  is a fragmentary, full sectional view of a portion of an automatic transmission including a drum brake assembly having an aluminum brake drum or housing having a thermally sprayed coating on its friction surface; 
           [0022]      FIG. 2  is a fragmentary sectional view of a portion of an automatic transmission including an aluminum clutch housing or support having a thermally sprayed coating on a seal surface; and 
           [0023]      FIG. 3  is a fragmentary sectional view of a portion of an automatic transmission including a unitary aluminum clutch housing or support having a thermally sprayed coating on a spline set and a bushing interface surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0025]    With reference to  FIG. 1 , a portion of a motor vehicle automatic transmission is illustrated and generally designated by the reference number  10 . The automatic transmission  10  includes a housing  12  which mounts, positions and protects various components such as an input shaft  14  a concentric quill  16 , a plurality of planetary gear assemblies  18 , one of which is illustrated in  FIG. 1 , fluid passageways  22  and a plurality of friction clutch assemblies  24 , one of which is also illustrated in  FIG. 1 . 
         [0026]    The automatic transmission  10  also includes a band brake assembly  30  which generally surrounds the aforementioned components and rotates on the axis of the input shaft  14  and the quill  16 . The band brake assembly  30  includes a cylindrical housing  32  which is supported on an anti-friction bearing  34  such as a ball or roller bearing assembly and coupled for rotation with a component such as a planet gear carrier  36  of the planetary gear assembly  18 . The cylindrical housing  32  of the band brake assembly  30  may take different forms or shapes such as axially shorter or longer or with a uniform outside diameter and the configuration illustrated should be understood to be exemplary and not limiting. 
         [0027]    The cylindrical housing  32  includes a fully circumferentially extending outer friction surface  40  which is generally surrounded by a brake band  42 . The brake band  42  includes clutch or brake friction material  44  on its inner surface facing and adjacent the outer friction surface  40  of the housing  32 . An actuator (not illustrated) which may be hydraulically, electrically or pneumatically operated and which may be under the control of a transmission control module (TCM) or similar engine or vehicular controller (all not illustrated) controls the action of the actuator and tightens the brake band  42  about the friction surface  40  of the cylindrical housing  32  to cease rotation of the housing  32  and any coupled or connected component or components and relaxes the brake band  42  to allow rotation thereof. 
         [0028]    The cylindrical housing  32  is fabricated of aluminum such as 5052 aluminum or a similar alloy and the entire outer friction surface  40  of the cylindrical housing  32  includes a thermally sprayed thin steel coating  50 . Prior to thermal spray coating, the outer friction surface  40  of the bell housing  32  preferably undergoes or includes a surface treatment which provides an irregular surface finish which improves adherence of the sprayed thin steel coating  50 . The thin steel coating  50  is preferably SAE 1008 or 1010 steel but may be other alloys, iron or other metals. The thin steel coating  50  on the housing  32  is then polished or undergoes similar surface treatment to obtain a desired smooth finish. The approximate finished thickness of the steel coating is 0.15 mm. (0.0059 inches) but may be thicker or thinner. The thermal spray process may be one of several similar processes, namely, high velocity oxygen fuel, powder plasma, plasma transferred wire arc or two wire arc. 
         [0029]    The cylindrical housing  32  of the band brake assembly  30  thus provides the weight saving and low inertia advantages of aluminum as well as the durability and service life of a steel band brake drum. 
         [0030]    Referring now to  FIG. 2 , another portion of a motor vehicle automatic transmission is illustrated and generally designated by the reference number  100 . The automatic transmission  100  includes a center shaft  112 , a quill  114  disposed concentrically about the center shaft  112 , a plurality of planetary gear assemblies (not illustrated), fluid passageways  116  and a plurality of friction clutch assemblies  118 , one of which is also illustrated in  FIG. 2 . The friction clutch assembly  118  includes a balanced hydraulic operator or actuator  120  having hydraulic fluid chambers  122  contained within an aluminum housing  124  which are selectively provided with pressurized hydraulic fluid through the fluid passageway  116  to engage and release the friction clutch assembly  118  and transmit torque therethrough. 
         [0031]    As is often the case, the fluid passageway  116  extends across and through two or more components of the automatic transmission  100  which may and typically will rotate at different speeds, Accordingly, it is necessary to both allow for such rotation between components and seal and restrict fluid flow to the desired path. As illustrated in  FIG. 2 , a pair of resilient seals  134  are seated in a corresponding pair of grooves  136  in an aluminum support  140  on opposite sides of the fluid passageway  116  to tightly seal the fluid passageway and direct fluid radially through the passageway  116  to the chambers  122  of the hydraulic operator  120 . 
         [0032]    As noted above, both the housing  124  and the support  140  are fabricated of aluminum or an aluminum alloy and the outer surface of the housing  124  adjacent the fluid passageway  116  and facing the resilient seals  134  and the interior surfaces of the pair of grooves  136  includes a thermally sprayed thin steel coating  150 . Prior to the thermal spray coating  150  being applied, the aluminum preferably undergoes a surface treatment to provide an irregular surface finish which improves adherence of the sprayed thin steel coating  150 . The thin steel coating  150  is preferably SAE 1008 or 1010 steel but may be other alloys, iron or other metals. The thin steel coating  150  on the outer surface of the housing  124  is then machined or undergoes similar surface treatment to obtain a desired final diameter of the housing  124  and finish of the thin steel coating  150 . The approximate finished thickness of the steel coating  150  is 0.15 mm. (0.0059 inches) but may be thicker or thinner. The thermal spray process may be one of several similar processes, namely, high velocity oxygen fuel, powder plasma, plasma transferred wire arc or two wire arc. 
         [0033]    Referring now to  FIG. 3 , another portion of a motor vehicle automatic transmission is illustrated and generally designated by the reference number  200 . The automatic transmission  200  includes a housing  212 , a rotating shaft or quill  214 , a plurality of planetary gear assemblies (not illustrated), a plurality of fluid passageways  216  and a plurality of friction clutch assemblies  218 , one of which is illustrated in  FIG. 3 . The friction clutch assembly  218  includes a balanced hydraulic operator or actuator  220  having hydraulic fluid chambers  224  contained within a unitary aluminum housing and hub assembly  230 . The hydraulic fluid chambers  224  are selectively provided with pressurized hydraulic fluid through the fluid passageways  216  to engage and release the friction clutch assembly  218  and transmit torque therethrough. Three resilient seals  226  in corresponding grooves  228  adjacent the fluid passageways  216  tightly seal and isolate the fluid passageways  216  and direct hydraulic fluid to the chambers  224  of the hydraulic operator or actuator  220   
         [0034]    The unitary aluminum housing and hub assembly  230  preferably combines into one component an “L” shaped housing portion  232  which extends radially and axially on the outside of the friction clutch assembly  218  and an irregular, generally cylindrical hub portion  234  which extends axially on the inside of the friction clutch assembly  218 . The housing portion  232  of the housing and hub assembly  230  includes a plurality of female splines  236  which engage and couple a plurality of reaction plates  238  in the friction clutch assembly  218  to the housing and hub assembly  230  as well as other components thereof. The hub portion  234  of the housing and hub assembly  230  also includes a plurality of female splines  240  which mate with a plurality of complementary male splines  244  on the shaft or quill  214  to transmit torque therebetween. The cylindrical hub portion  234  of the housing and hub assembly  230  also includes a bushing interface surface  251 . 
         [0035]    The plurality of female splines  240  includes a thermally sprayed thin steel coating  250 . Prior to the thermal spray coating  250  being applied, the plurality of aluminum female splines  240  preferably undergoes a surface treatment to provide an irregular surface finish which improves adherence of the sprayed thin steel coating  250 . The thin steel coating  250  is preferably SAE 1008 or 1010 steel but may be other alloys, iron or other metals. The thin steel coating  250  on the plurality of female splines  240  is then machined or undergoes similar surface treatment to obtain a desired size and geometry of the female splines  240  and the finish of the thin steel coating  250  if needed. The approximate finished thickness of the steel coating  250  is 0.15 mm. (0.0059 inches) but may be thicker or thinner. The thermal spray process may be one of several similar processes, namely, high velocity oxygen fuel, powder plasma, plasma transferred wire arc or two wire arc. 
         [0036]    The bushing interface surface  251  also includes a thermally sprayed thin steel coating  252 . Prior to the thermal spray coating  252  being applied, the bushing interface surface  251  preferably undergoes a surface treatment to provide an irregular surface finish which improves adherence of the sprayed thin steel coating  252 . The thin steel coating  252  is preferably SAE 1008 or 1010 steel but may be other alloys, iron or other metals. The thin steel coating  252  on the bushing interface surface  251  is then machined or undergoes similar surface treatment to obtain a desired size and geometry of the bushing interface surface  251  and the finish of the thin steel coating  252  if needed. The approximate finished thickness of the steel coating  252  is 0.15 mm. (0.0059 inches) but may be thicker or thinner. Once again, the thermal spray process may be one of several similar processes, namely, high velocity oxygen fuel, powder plasma, plasma transferred wire arc or two wire arc. 
         [0037]    The unitary aluminum housing and hub assembly  230  of the present invention combines into a single aluminum component what was heretofore two components including a steel hub which was riveted to or serrated and press fit onto the housing. Additionally, the unitary aluminum housing and hub assembly  230  provides weight savings in a component that may be retrofit into the same applications and occupies the same or less packaging space. 
         [0038]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.