Patent Application
20050173973
The present invention generally relates to drive line power transfer mechanisms and more particularly, to drive line 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'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.
In one preferred form, the present invention provides a axle assembly having a housing, a power transfer mechanism and a fluid. The housing has a wall member that defines a cavity. The power transfer mechanism is positioned within the cavity. The fluid extracts heat from the power transfer mechanism during operation of the drive line power transfer assembly. The fluid transfers the heat to the wall member via an inside surface of the wall member and the wall member transfers this heat to the ambient air via the outside surface of the wall member. The axle assembly further includes an wheel located outside the housing which is operably coupled to the power transfer mechanism for rotation therewith. The wheel includes at least one duct that is adapted to pump air to the outside surface of the differential thereby increasing the cooling capacity associated with the power transfer assembly.
In another form the present invention provides a generally solid body bounded by an annular leading surface, an annular trailing surface, and an outer surface, wherein the leading surface and the trailing surface are generally parallel, the body having a central bore and a plurality of radially spaced apertures extending therethrough from the leading surface to the trailing surface wherein the central bore is adapted to restrain the wheel for rotation with a shaft and the radially spaced apertures are adapted to draw a fluid therethrough during said rotation
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.
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:
The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. In particular, the present invention is directed to an improved axle assembly of the type used in motor vehicle drive train applications. The axle assembly of the present invention includes a cooling pump to pump air to the outside of the differential assembly thereby lowering the operating temperature without a major modification to an existing axle assembly. To accomplish this end, an wheel is provided to rotate with the rotational members of the axle assembly and pump air to the outside of the differential. The axle assembly of the present invention further enables improved manufacturing of the axle assembly due to the simplified task of attaching the wheel to the yoke and pinion shaft during manufacture. This method further enables a retrofit of existing vehicles. Thus, the axle assembly of the present invention may be utilized with a wide variety of applications and is not intended to be specifically limited to the particular application recited herein.
With particular reference now to
Referring now to
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 axle housing 34 through outside surface 72. The amount of heat removed from outside surface 72 depends upon the volumetric airflow across axle housing 38. 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 would 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
Wheel 66 is further shown to include at least one duct 100 formed therein. Duct 100 is 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
Referring now to
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 the outer surface 134 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
Referring now to
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.
