Patent Application
20050150325
The subject invention generally relates to a drive axle assembly including a pumping mechanism for maintaining a dual fluid level within the axle assembly. More specifically, the subject invention utilizes the pumping mechanism to maintain a first fluid level within an axle housing and a second, higher, fluid level within a wheel end gear housing.
Many drive axle assemblies utilize gear sets at wheel ends to increase torque output. The gear sets are driven by axle shafts that receive driving input torque from a center differential gear assembly. The axle shafts and center differential gear assembly are enclosed within an axle housing and the wheel end gear sets are enclosed within gear housings mounted to opposing ends of the axle housing.
In order for the center differential gear assembly and the wheel end gear sets to operate smoothly and efficiently, proper lubrication should be maintained. Traditionally, the axle assembly is filled with a lubrication fluid until both the axle housing and gear housing are filled to sufficient lubrication levels. This requires a significant amount of lubricating fluid. Further, the axle housing can be overfilled with fluid in order to achieve the desired fluid levels in the gear housings. This can decrease the overall operating efficiency of the drive axle assembly.
There is a need for a drive axle assembly that can maintain different fluid levels in axle and wheel end gear housings in order to reduce the amount of lubricating fluid needed, in addition to overcoming the other above-mentioned deficiencies in the prior art.
A drive axle assembly includes a wheel end gear set that is driven by an axle shaft. The axle shaft is substantially enclosed within an axle housing and the wheel end gear set is substantially enclosed within a gear housing. A first fluid level is maintained in the axle housing and a second fluid level, different from the first fluid level, is maintained in the gear housing. A pumping mechanism is driven by the axle shaft to pump fluid from the first fluid level to the second fluid level.
In one disclosed embodiment, the second fluid level is vertically higher than the first fluid level and the pumping mechanism pumps fluid from the lower axle housing level to the higher gear housing level. Preferably, the pumping mechanism is an impeller that is mounted for rotation with the axle shaft. An impeller housing is positioned between the axle housing and gear housing and defines a fluid cavity. The impeller is mounted within the fluid cavity. The impeller moves the fluid from a center portion of the axle housing into the fluid cavity producing a fluid dam. As the impeller continues to move the fluid, the fluid level in the cavity rises. The fluid rises until the fluid reaches a fluid port that fluidly communicates with the gear housing. Preferably, this fluid port is positioned at the second fluid level.
In one disclosed embodiment, the impeller comprises a center tubular portion and a plate portion. The plate portion is an auger shaped member that is welded or similarly attached to the center tubular portion. The tubular portion is preferably press-fit onto the axle shaft. The auger shaped member comprises a disc-shape that includes at least first and second radially extending edges. The first and second edges are laterally spaced apart from each other along an external surface of the tubular member to define a fluid path. As the axle shaft rotates the impeller, fluid is drawn from the center portion of the axle housing, through the fluid path in the impeller, and into the fluid cavity of the impeller housing.
The subject invention provides a simplified method and apparatus for maintaining dual fluid levels in a drive axle assembly, which reduces the amount of fluid needed to maintain adequate lubrication. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
A drive axle assembly incorporating the subject invention is shown generally at 10 in
The wheel end assemblies 22 each include a gear set 24 that is driven by one of the axle shafts 20, and which in turn drives a vehicle wheel 26. The gear sets 24 can be planetary, helical, or any other type of wheel end gear set known in the art. The gear sets 24 provide for increased output torque at the wheels 26 for heavy-duty vehicle applications.
An axle housing 28 substantially surrounds and encloses the axle shafts 20 and the differential assembly 18. The gear sets 24 each include a gear housing 30 that substantially surrounds and encloses the gear sets 24. The gear housings 30 are positioned at opposing ends of the axle housing 28.
The axle 28 and gear 30 housings are partially filled with a lubricating fluid to ensure that the gear sets 24, differential assembly 18, and associated bearings are protected from overheating and wear. The drive axle assembly 10 maintains a dual fluid level within the axle 28 and gear 30 housings, i.e. a first predetermined fluid level 32 is maintained in the axle housing 28 and a second predetermined fluid level 34 is maintained in the gear housings 30. A pumping mechanism 36 is driven by the axle shafts 20 to move the lubricating fluid from a center section of the axle housing 28 to the gear housings 30. The lubricating is preferably an oil-based fluid, however, other lubricating fluids known in the art could also be used.
The pumping mechanism 36 is shown in greater detail in
A fluid port 46 is formed within a wall 48 of the impeller housing 42. The wall 48 can be integrally formed within the impeller housing 42 or can be a separate cover plate for the impeller housing 42. The fluid port 46 provides fluid communication from the fluid cavity 44 to a gear cavity 50 defined by the gear housing 30. The wheel end gear set 24 includes a plurality of gears 52 and bearings 54 that are positioned within the gear cavity 50.
The axle shaft 20 drives the impeller 38, which moves the fluid from the center section of the axle housing 28 into the fluid cavity 44, producing a fluid dam. As fluid continues to flow from the lower level center section of the axle housing 28 and into the fluid cavity 44, the fluid level also continues to rise within the cavity 44 until the fluid passes through the fluid port 46. Preferably, the fluid port 46 is positioned at the desired second fluid level 34 for the gear housing 30. An overflow or return port 56 is also formed in the impeller housing 42 or gear housing 30 at a vertically higher position than the fluid port 46. If the fluid in the gear housing 30 rises above the predetermined second fluid level 34, fluid will flow out of the overflow port 56 and back into the axle housing 28.
The desired flow rate can be tailored by varying the wall clearance between the impeller 38 and the wall 48 of the impeller housing 42. In other words, the flow rate can be varied by adjusting the lateral position of the impeller 38 along the axle shaft 20 relative to the wall 48. The flow rate could also be varied by increasing or decreasing the size of the fluid port 46 and/or overflow return port 56 back to the axle housing 28.
The impeller 38 is shown in greater detail in
The plate portion 62 is preferably an auger shaped member. The auger shaped member comprises a disc 70 having an inner circumference 72 attached to the external circumferential surface 68 of the tube portion 60. Preferably, the disc 70 is welded to the tube portion 60, however, other similar attachment methods could also be used. As discussed above, the disc 70 is preferably made from stamped plate component that is thin in cross-section. Because the cross-section is thin, there are minimal losses due to churning and noise is not generated.
The disc 70 has a first radially extending edge 72 and a second radially extending edge 74. The edges 72, 74 are laterally spaced apart from each other along the external circumferential surface 68 of the tube portion 60 to define a fluid path or gap 76. This configuration is achieved by providing a radial cut on the disc 70 from the inner circumference 72 to an outer circumference 78. The stamped disc 70 is then stretched in a lateral direction, parallel to the axle shaft 20, such that the first and second edges 72, 74 are spaced apart from each other. The disc 70 is then welded to the tube portion 60. Fluid flows from the axle housing 28 through the fluid gap 76 and into the fluid cavity 44 of the impeller housing 42.
The subject invention provides a cost effective method and apparatus for maintaining a dual level fluid system within a drive axle assembly 10 that includes wheel end gear sets 24. By utilizing a dual fluid level system, lower quantities of lubricating fluid can be used, which reduces system cost and maintenance cost. Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
