Abstract:
An axle assembly with a cooling pump. The cooling pump includes a disk-shaped wheel with a plurality of radially-spaced ducts formed therein. The wheel is positioned in proximity to the axle assembly and rotated, allowing the ducts to draw air therethrough and direct the air to the axle assembly.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to driveline power transfer mechanisms and more particularly, to driveline power transfer mechanisms that include a cooling system. 
     Modern vehicles typically include an axle assembly having a housing and a differential assembly. The housing includes a cavity into which the differential assembly is rotatably disposed. The differential assembly is mechanically coupled to the vehicle&#39;s engine by a drive shaft. The differential assembly is also coupled to the vehicle drive wheels via a pair of axle shafts. The differential assembly regulates the drive torque between the axle shafts thereby causing the shafts to rotate. During operation of the vehicle, friction between the various components of the differential assembly generates heat, which if unabated could decrease the useful life of the axle assembly. A lubricating fluid, which is contained within the cavity of the axle assembly is therefore typically employed to remove heat from the various components of the differential assembly. The lubricating fluid then rejects, or transfers, this heat to the housing, which, in turn, rejects or transfers this heat via convection, conduction, and radiation to the environment in which the vehicle is operating. 
     Current advances in the fuel efficiency of vehicles have resulted in decreased air flow under the vehicle, which significantly reduces the capability of the housing of the axle assembly to reject heat. 
     One solution that has been suggested utilizes a dedicated heat exchanger for removing heat from the housing of the axle assembly. Several drawbacks have been noted with this approach, however. For example, the viscosity of the lubricating fluids in an axle assembly is such that the lubricating fluid is relatively difficult to pump, particularly when the ambient air temperature is relatively low. Another drawback concerns the cost of the pumps and heat exchangers used in these systems. 
     In view of the aforementioned drawbacks, there remains a need in the art for an axle assembly having a cooling system that provides improved cooling of the axle lubricant and axle assembly components. 
     SUMMARY OF THE INVENTION 
     In one form, the present teachings provide a vehicle driveline component that includes a housing, a power transfer mechanism and a wheel. The housing defines a chamber. The power transfer mechanism has a shaft that is supported for rotation by the housing and which extends outwardly from the housing. The wheel is coupled to the shaft for rotation therewith. The wheel includes a leading surface and a trailing surface and defines a duct that extends through the leading surface and the trailing surface. The duct is configured to draw air therethrough when the wheel is rotated. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of an exemplary motor vehicle into which the axle assembly constructed in accordance with the teachings of the present invention is incorporated; 
         FIG. 2  is a schematic view of the drivetrain of the motor vehicle of  FIG. 1 ; 
         FIG. 3  is a plan view of the differential portion of an axle assembly of the drivetrain in  FIG. 2 ; 
         FIG. 4  is a side view of the differential of  FIG. 3 ; 
         FIG. 5  is a perspective view of the wheel shown in  FIG. 3 ; 
         FIG. 6  is a side view of the wheel of  FIG. 5 ; 
         FIG. 7  is a front view of the wheel of  FIG. 5 ; 
         FIG. 8  is a plan view of a conventional duct within a streamline body; 
         FIG. 9  is a sectional view taken along line  9 — 9  of  FIG. 8 ; and 
         FIG. 10  is an alternate embodiment of the wheel of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the illustrated embodiment is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. drivetrain Although the particular vehicle driveline component described herein and illustrated in the attached drawings is an axle assembly, those of ordinary skill in the art will appreciate that the disclosure, in its broadest aspects, has applicability to various other types of vehicle driveline components. 
     With particular reference now to  FIG. 1 , an exemplary motor vehicle is generally indicated by the reference numeral  10 . Vehicle  10  can include a body  12 , an underbody  14 , and a drivetrain  20 . Referring now to  FIG. 2 , drivetrain  20  can include an engine  22 , a transmission  24 , which has an output shaft  26 , and a propeller shaft  28  that can connect output shaft  26  to a pinion shaft  30  of a rear axle assembly  32 . Rear axle assembly  32  includes an axle housing  34 , a differential assembly  36 , which is supported in axle housing  34 , and a pair of axle shafts  38  and  40 , respectively that are interconnected to left and right rear wheels  42  and  44 , respectively. Pinion shaft  30  has a pinion shaft gear  46  fixed thereto which drives a ring gear  48  that is fixed to a differential casing  50  of differential assembly  36 . A gear set  52  supported within differential casing  50  transfers rotary power from differential casing  50  to output shafts  54  and  56  connected to axle shafts  38  and  40 , respectively, and facilitates relative rotation therebetween. While differential assembly  36  is shown in a rear wheel drive application, it is contemplated that the teachings of the present disclosure can be employed with other vehicle driveline components, including differential assemblies installed in transaxles for use in front wheel drive vehicles and/or in transfer cases for use with four wheel drive vehicles. 
     Referring now to  FIGS. 3 and 4 , axle assembly  32  is described in detail. Differential assembly  36  is a parallel axle type differential that includes an axle housing  34  that defines an internal chamber  58  with a lubricating fluid  60  contained therein. Pinion shaft  30  connects to propeller shaft  28  via a yoke  62  that is operably connected to pinion shaft  30  for rotation therewith. A wheel  66  is interposed between differential assembly  36  and yoke  62  such that wheel  66  is coupled for rotation with yoke  62  and pinion shaft  30 . In the particular example provided, wheel  66  is bolted to pinion shaft  30  and yoke  62 , but those skilled in the art will appreciate that wheel  66  could be coupled to pinion shaft  30  and/or yoke  62  in any appropriate manner. Axle housing  34  includes an inside surface  70  and an outside surface  72 . Lubricating fluid  60  is in contact with ring gear  48  and gearset  52  and receives heat therefrom. Lubricating fluid  60  is in contact with inside surface  70  of axle housing  34  for transfer of heat thereto. 
     During operation of vehicle  10  the internal moving components of axle assembly  32 , including gearset  52 , pinion shaft gear  46 , and ring gear  48 , produce heat. This heat is transferred to lubricating fluid  60  and then transferred to axle housing  34 , via inside surface  70 , and then out of axle housing  34  through outside surface  72 . The amount of heat removed from outside surface  72  depends upon the volumetric airflow across axle housing  34 . As vehicle  10  is moving, airflow across outside surface  72  results in forced air convection, which can be supplemented with the air supplied by wheel  66 , as discussed below. While axle housing  34  is shown to include a smooth outer outside surface  72 , it will be appreciated that outside surface  72  could be provided with fins that could add to the structural stiffness and/or heat dissipation capability of outside surface  72 . 
     With reference now to  FIGS. 5–7 , wheel  66  is described in greater detail. Wheel  66  is shown to include a cylindrical outer surface  80 , an annular leading surface  82 , an annular trailing surface  84  and an inner cylindrical surface  86  defining a central bore  88 . As best seen in  FIG. 7 , wheel  66  further includes a partial cylindrical bore  90  that intersects leading surface  82  and forms a recessed cylindrical surface  92  and a recessed annular surface  94 . Mounting apertures  96  are formed within wheel  66  from recessed annular surface  94  to trailing surface  84 . Mounting apertures  96  are provided for attachment of wheel  66  to yoke  62  and/or pinion shaft  30 . 
     Wheel  66  is further shown to include at least one duct  100  formed therein. Duct  100  can be defined by a leading edge  102 , a lip  104 , a ramp  106 , ramp walls  108 , and an outlet  110 . Outlet  110  defines an aperture within trailing surface  84 . Leading edge  102 , lip  104 , and ramp walls  108  intersect leading surface  82  to define an opening  112 . While outer surface  80  is illustrated as a cylindrical surface, it would be appreciated that outer surface  80  could be other shapes, such as frusto-conical or a plurality of intersecting polygons, depending upon the relative geometry of leading surface  82  and trailing surface  84 . 
     Duct  100  is shown in  FIGS. 5–7  to be a variable area duct such as detailed in National Advisory Committee for Aeronautics (NACA), Advance Confidential Report 5120 of Nov. 13, 1945, declassified version dated Jul. 3, 1951, “An Experimental Investigation of NACA, Submerged-Duct Entrances.” The geometry of duct  100  is formed to allow duct  100  to perform similar to a variable geometry NACA duct as discussed herein. 
     Referring now to  FIGS. 8 and 9 , a streamline body  120  is illustrated to include an outer surface  124  with a NACA duct  130  formed therein. NACA duct  130  is defined by a leading edge  132 , a lip  134 , a ramp  136 , a pair of ramp walls  138  and a centerline C. The distance between leading edge  132  and lip  134  along centerline C is illustrated as length L. Lip  134  has a width W. Ramp walls  138  and ramp  136  are formed to converge as they approach lip  134 . Thus formed, the cross-sectional area of duct  130  taken normal to centerline C increases from leading edge  132  to lip  134 . 
     Laminar air flow in the direction of arrow F across streamline body  120  creates a boundary layer of air immediately adjacent streamline body  120 . As the boundary layer encounters the leading edge  132  of NACA duct  130 , the flow area available to the boundary layer increases. This increase in flow area provides a localized reduction in air pressure within the boundary layer. As the boundary layer continues to flow along the length L of the NACA duct  130  from the leading edge  132  to the lip  134 , the curvature of the ramp walls  138  and the angle of the ramp  136  relative to the outer surface  124  of the streamline body  120  create a further increase in flow area available to the boundary layer of air and a resulting further decrease in localized air pressure within the boundary layer. This decreased localized air pressure zone is defined by the air within the duct and immediately adjacent the duct opening. This decrease in air pressure results in an increase in air velocity. The resulting low pressure acts to draw or suck air into the duct opening formed in the outer surface  124  by creating a vacuum effect. The air drawn into duct  130  is then directed to a preselected air intake, such as an engine intake or cooling surface. 
     The vacuum effect does not impart a significant amount of turbulence in the boundary layer. In contrast, an air scoop that is positioned into the path of the boundary layer will divert air into an opening in a surface of a streamline body by pushing the air into the surface opening. This pushing of air, however, creates a reactive force within the scoop and creates drag in the boundary layer as turbulence is imparted to the boundary layer downstream of the scoop along the streamline body. Thus provided, a conventional NACA duct  130  draws in a portion of air from a boundary layer as the boundary layer of air passes the opening of the NACA duct  130 , thus diverting air with negligible turbulence. The present invention utilizes this vacuum creating effect to suck air into ducts  100 , as described below. As illustrated, NACA duct  130  is symmetrical along centerline C, although it will be appreciated by one skilled in the art that a duct need not be symmetrical to operate in the manner described above. 
     As best seen in  FIGS. 5 and 6 , the direction of travel, as indicated by arrow T, of vehicle  10  provides a resultant airflow generally in the direction of arrow A. This airflow impacts leading surface  82  and builds a resulting air pressure gradient along leading surface  82  with a higher pressure found adjacent leading surface  82 . Layers of air adjacent leading surface  82  are represented as L 1 , L 2 , and L 3 , wherein the air pressure within layer L 1  is greater that the air pressure within layer L 2 , and the air pressure within layer L 2  is greater that the air pressure within layer L 3 . Travel of vehicle  10  in direction T also results in rotation of wheel  66  in the direction shown in  FIG. 5 . As best seen in  FIGS. 5 and 7 , duct  100  is formed in wheel  66  such that leading edge  102  is followed by lip  104  as wheel  66  rotates in the direction of arrow R. As wheel  66  rotates, ducts  100  create locations of localized low pressure within openings  112 , in the same manner as discussed above with reference to the operation of a NACA duct  130 . These locations of localized low pressure pull air from layer L 1  into openings  112 . Rotation of wheel  66  allows ducts  100  to draw in air which is expelled through outlets  110  and onto outside surface  72  of axle housing  34 . This decrease in pressure within ducts  100  results in an increase in velocity for a gas such as air. This increase in velocity of air provides for a larger volumetric air flow directed to exterior surface  72  of axle housing  34  thereby providing a greater amount of heat dissipation from axle assembly  32 . Further travel of vehicle  10  causes further rotation of wheel  66  and additional air to encounter leading surface  82 . This further rotation of wheel  66  draws the additional air into ducts  100 . Thus provided, wheel  66  provides a device useful to draw air and increase the velocity of the air to provide a greater cooling capacity to an existing assembly. 
     Referring now to  FIG. 10 , an alternate embodiment of wheel  66  is shown as an wheel  266  including a plurality of ducts  200 , a cylindrical outer surface  280 , an annular leading surface  282 , and an annular trailing surface  284 . Each duct  200  is defined by a leading edge  202 , a lip  204 , a ramp  206 , ramp walls  208 , and an outlet  210  that intersects trailing surface  284 . Leading edge  202 , lip  204 , and ramp walls  208  intersect leading surface  282  to define an opening  212 . Opening  212  has a generally oval cross section and ramp  206  is curved and integral with ramp walls  208 . Wheel  266  operates in a manner similar to wheel  66  as discussed herein. 
     While ducts  100 ,  130  and  200  are illustrated with specific geometries, it would be appreciated by one skilled in the art that a duct of any other geometry within an wheel that is designed to draw air into the duct from an adjacent air layer could be utilized to produce a similar result. 
     The description of the invention is merely exemplary in nature and, thus, 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. 
     The curvature of ramp walls  138  relative the centerline C of NACA duct  130  is represented in Table 1 wherein the relationship between a distance x along centerline C from lip  134  and a corresponding distance y is tabulated. Distance y is the distance from the centerline C at distance x to the ramp walls  138 . 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 x/L 
                 y/B 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.0 
                 0.500 
               
               
                   
                 0.05 
                 0.4930 
               
               
                   
                 0.10 
                 0.4670 
               
               
                   
                 0.20 
                 0.3870 
               
               
                   
                 0.30 
                 0.3100 
               
               
                   
                 0.40 
                 0.2420 
               
               
                   
                 0.50 
                 0.1950 
               
               
                   
                 0.60 
                 0.1550 
               
               
                   
                 0.70 
                 0.1200 
               
               
                   
                 0.80 
                 0.0750 
               
               
                   
                 0.90 
                 0.0575 
               
               
                   
                 1.00 
                 0.0440