Abstract:
A clutch hub is splined to a planetary ring gear and a second rotating element, coupling the two elements. The spline defines a number of axial fluid distribution channels that conduct fluid from an interior radial passageway beside the ring gear to exterior radial passageways over the ring gear. These axial passageways permit packaging the clutch pack directly over the ring gear without drilling holes in the hardened gear material. The axial channels may be defined by radial space between the splined components. Alternatively or additionally, some spline teeth may be omitted to define larger axial channels.

Description:
TECHNICAL FIELD 
     This disclosure relates to the field of transmissions for motor vehicles. More particularly, the disclosure pertains to a transmission having a clutch hub splined to a ring gear to create an axial fluid distribution channel. 
     BACKGROUND 
     Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Most types of internal combustion engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. 
     Many transmissions utilize friction clutches and brakes which are engaged in different combinations to establish different power flow paths having different speed ratios. One type of commonly used friction clutch is a wet multi-plate clutch. A clutch pack includes a set of friction plates splined to one component and interleaved with a set of separator plates splined to a different component. To engage the clutch, pressurized fluid is supplied to an apply chamber forcing a piston to squeeze the friction plates between the separator plates. Friction between the friction plates and separator plates prevents relative rotation coupling the two components to each other. When the fluid pressure is reduced, a return spring forces the piston away from the clutch pack removing the normal force such that relative rotation is possible with minimal drag. Wet multi-plate clutches rely on a supply of transmission fluid to the friction material on the friction plates. This fluid serves several purposes, including modifying the friction characteristics of the material and removing excess heat. 
     SUMMARY OF THE DISCLOSURE 
     A transmission includes a planetary gearset ring gear, a clutch hub, and a plurality of friction plates. The clutch hub has internal and external spline teeth. The internal spline teeth engage with ring gear spline teeth to define a plurality of axial distribution channels. The clutch hub further defines one or more radial channels extending outwardly from the axial channels. The friction plates are axially aligned with the ring gear. The clutch hub may be closed on one end to define one end of the fluid distribution channels. A snap ring may be inserted into a groove of the clutch hub to define an end of the axial distribution channels. A rotating shaft may also be splined to the clutch hub. The space between the rotating shaft and the ring gear may define a radial fluid flow channel extending inwardly from the axial channels. The axial channels may be defined between an inner diameter of the ring gear spline teeth and an outer diameter of the clutch hub internal spline teeth. Alternatively or additionally, some internal spline teeth may be omitted to define axial fluid flow channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a transmission kinematic arrangement. 
         FIG. 2  is a cross section of a portion of a transmission according to the kinematic arrangement of  FIG. 1 . 
         FIG. 3  is an end view of a first embodiment of a ring gear and clutch hub in the transmission of  FIG. 2 . 
         FIG. 4  is an end view of a second embodiment of a ring gear and clutch hub in the transmission of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
       FIG. 1  illustrates a kinematic arrangement for a  10  speed automatic transmission. Four simple planetary gear sets  20 ,  30 ,  40 , and  50  each have a carrier supporting a set of planet gears with each planet gear meshing with a sun gear and a ring gear. Sun gears  26  and  36  are fixedly coupled. Carrier  22  is fixedly coupled to ring gear  58 , Ring gear  38  is fixedly coupled to sun gear  46 . Ring gear  48  is fixedly coupled to sun gear  56 . Input  60  is fixedly coupled to carrier  32 . Output  62  is fixedly coupled to carrier  62 . Brake  66  selectively holds ring gear  28  against rotation. Brake  68  selectively holds sun gears  26  and  36  against rotation. Clutch  70  selectively couples input  60  and carrier  32  to ring gear  48  and sun gear  56 . Intermediate shaft  64  is selectively coupled to carrier  42  by clutch  72 , selectively coupled to carrier  22  and ring gear  58  by clutch  74 , and selectively coupled to ring gear  38  and sun gear  46  by clutch  76 . 
     In order to minimize the overall length and diameter of the transmission, it is desirable to nest components closely whenever possible, as long as the nesting does not interfere with component function. Specifically, it is desirable to locate the friction plates and separator plates of clutch  76  radially outside ring gear  38  and at the same axial position. Conventionally, fluid is directed into a space on the radial interior side of a clutch hub from which centrifugal force pushes the fluid through radial holes in the clutch hub to lubricate and cool the clutch pack. However, when a clutch pack is located adjacent to and radially outside a ring gear, the space is occupied by a solid ring gear. Drilling diagonal holes through the ring gear is difficult because the ring gear is made of hardened material for strength. Consequently, it is sometimes necessary to offset the clutch pack axially from the ring gear which may increase the overall length of the transmission. 
       FIG. 2  is a cross section showing gear set  30  and clutch  76  in more detail. Carrier  32  is splined to input shaft  60 . Planet gear  34  is supported for rotation with respect to carrier  32  by roller bearings. Sun gear  36  is splined to shaft  80  which couples it to sun gear  26 . Clutch hub  82  is splined to both ring gear  38  and shaft  84  which is coupled to sun gear  46 . A plurality of friction plates  86  are splined to clutch hub  82  and interleaved with a plurality of separator plates  88  splined to intermediate shaft  64 . The leftmost separator plate, which is called a reaction plate, is constrained axially by snap ring  90 . Piston  92  slides axially with respect to intermediate shaft  64  in response to fluid pressure to squeeze friction plates  86  between separator plates  88 . 
     Fluid is supplied for a variety of purposes through various axial channels  94  in input shaft  10 . One of these channels conveys fluid at low pressure for lubrication and heat removal. The lubrication channel in the input shaft supplies fluid to an axial channel  96  in carrier  32 . Some of this fluid is conveyed to the roller bearings and then through the planet gears  34  to lubricate the meshing interfaces with sun gear  36  and ring gear  38 . The remainder of this fluid continues flowing radially to the cavity created by ring gear  38  and shaft  84 . Alternatively, the fluid may flow into this cavity through the thrust bearings separating shaft  80 , carrier  32 , and shaft  84 . In the alternative configuration, some of the fluid may be captured as it flows radially and diverted to lubricate the planetary gears. From the cavity, the fluid flows radially through channel  98  to the inner surface of clutch hub  82 . Channel  98  may be formed into shaft  84  or may be defined by the interface between ring gear  38  and shaft  84 . From channel  98 , the fluid flows axially through one or more axial channels formed by the spline interfaces between clutch hub  82  and ring gear  38  and shaft  84 . The flow toward the left is contained by a lip formed into the end of clutch hub  82 . The flow toward the right is contained by snap ring  100 . From the axial channels, the fluid flows through radial channels  102  in clutch hub  82  and into clutch pack. As the fluid flows radially through the clutch pack, it absorbs heat and controls the friction properties to improve controllability during shifts. The axial channels permit fluid flow to reach friction plates that are located directly over the ring gear  38  without any need to drill holes in ring gear  38 . 
       FIG. 3  is an end view of one embodiment of clutch hub  82  and ring gear  38 . Ring gear  38  has a number of external spline teeth  104  that mesh with internal spline teeth  106  of clutch hub  82 . Clutch hub  82  also has a number of external spline teeth  108  that mesh with friction plates  86 . The inner diameter of the clutch hub internal spline teeth  106  is greater than the inner diameter of the ring gear external spline teeth  104  defining a gap  110 . The gap  110  is an axial channel conducting fluid from radial channels  98  to radial channels  102 . The number of radial channels  102  at a given axial location can be equal to the number of spline teeth providing excellent distribution of the fluid across the surfaces of the friction plates. 
       FIG. 4  is an end view of another embodiment of clutch hub  82  and ring gear  38 . In this embodiment, one of the internal spline teeth of clutch hub  82  is omitted, forming an axial channel  110 ′ which is significantly larger than the axial channels of  FIG. 3 . Several internal spline teeth may be omitted around the perimeter of ring gear  38  to form a number of such large axial channels. A similar effect can be achieved by omitting ring gear spline teeth. These larger channels are capable of transferring fluid a higher flow rates than the channels of  FIG. 3 . However, the number of radial channels  102  is reduced, so the groove pattern of friction plates  86  and relative rotation between friction plates  86  and separator plates  88  is more important to distribute the fluid. The two approaches may be used in combination. 
     In addition to the packaging advantages of being able to position the clutch pack over the ring gear, this arrangement offers manufacturing cost advantages. The clutch hub can be formed easily from sheet metal. The ring gear, on the other hand is typically formed using more expensive processing including heat treated for hardness. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.