Differential assembly with inverted bearing

A differential includes first and second case members that are attached to each other to define an inner cavity that receives a differential gear assembly. A first tapered roller bearing is associated with the first case member and a second tapered roller bearing is associated with the second case member. One of the first and second tapered roller bearings is inverted such that a defining taper diverges towards the differential gear assembly. The other of the first and second tapered roller bearings is non-inverted with a defining taper diverging in a direction that faces away from the differential gear assembly.

TECHNICAL FIELD

A differential assembly is configured to include an inverted tapered roller bearing associated with one differential case half.

BACKGROUND OF THE INVENTION

A traditional differential assembly includes a first differential case half, a second differential case half, and a ring gear that are attached to each other to form a differential unit. A differential gear assembly is enclosed within a cavity formed within the first and second differential case halves. The first and second differential case halves are often referred to as a plain case half and a flange-side case half. A first tapered roller bearing is mounted to the flange-side case half and second tapered roller bearing is mounted to the plain case half.

The differential unit is installed into a carrier associated with a drive axle. Each of the first and second differential case halves includes a bearing journal that accepts a tapered roller bearing cone for the first and second tapered roller bearings. Bores in the carrier accept corresponding tapered roller bearing cups. The first and second tapered roller bearings are oriented such that an apex of each taper points in a direction away from the differential gear assembly.

One disadvantage with this traditional configuration concerns the first tapered roller bearing, which is associated with the flange-side case half. Packaging constraints prevent this flange-side bearing from favorably straddling gear forces, e.g. the flange-side bearing is positioned such that the flange-side bearing reacts most of the load from gear forces. This is especially true for a tandem axle configuration where a through-shaft, which transfers driving input to a rear-rear axle, passes through a hollow pinion input gear. To accommodate these high reaction forces, a large, high-cost bearing is required in order to meet durability requirements. The large reaction forces also result in high stress levels on a flange-side bearing journal. These stress levels in turn drive the need for more expensive differential case materials and/or expensive processing steps (induction hardening, for example) in order to meet durability requirements. This adds further cost to the product.

Another disadvantage with the traditional configuration is that assembly of the differential assembly into the carrier is highly constrained due to requirement of a one-piece flange-side bearing support. The one-piece flange-side bearing support is required because a two piece leg cap cannot package inside the available space. To assemble the differential assembly into the carrier, the differential assembly must be swung through an opening in a carrier housing such that the flange-side bearing and cone can be fitted into an associated cup. Sufficient clearances must be incorporated into the carrier housing to allow for the differential assembly to be installed without contacting any carrier structures. This increases the weight and cost of the carrier and increases the volume of the lubricant required.

Thus, there is a need for an improved differential configuration that facilitates assembly, reduces cost, and more evenly distributes gear loading, as well as overcoming other above-mentioned deficiencies in the prior art.

SUMMARY OF THE INVENTION

A differential includes first and second case members that are attached to each other to provide an internal cavity that receives a differential gear assembly. A first bearing is associated with the first case member and a second bearing is associated with the second case member. The first and second bearings are tapered roller bearings with one of the bearings being installed in an inverted position where a defining taper extends in a direction facing the differential gear assembly.

In one example, the first case member is a plug case half and the second case member is a plain case half. A first tapered roller bearing is installed on the plug case half and is inverted such that an apex of the defining taper points towards the differential gear assembly. A second tapered roller bearing is installed on the plain case half and is non-inverted such that an apex of a defining taper points in a direction facing away from the differential gear assembly.

In this configuration, the plug case half includes a bore that accepts a bearing cup. A trunnion, mounted to a carrier housing, includes a journal feature that accepts the bearing cone for the first tapered roller bearing. The plain case half includes an outer circumferential surface that accepts a bearing cone. The carrier housing provides support for another bore that accepts the bearing cup for the second tapered roller bearing.

This configuration facilitates assembly of the differential into a carrier by requiring smaller swing clearances compared to traditional configurations. This feature reduces carrier size, weight, and cost as well as reducing required lubricant volume. The bearing cup for the first tapered roller bearing is installed within the bore of the plug case half and the bearing cone for the second tapered roller bearing is installed onto the outer circumferential surface of the plain case half to form a bearing and differential case unit. The bearing and differential case unit is then inserted into the internal cavity by rotating, i.e. swinging, the bearing and differential case unit through an opening in the carrier such that the bearing cup surrounds the bearing cone of the first tapered roller bearing.

The configuration also provides easy setting and adjustment of gear backlash and bearing preloads. In one embodiment, one of the first and second tapered roller bearings is shimmed to adjust gear backlash, and a single adjusting ring, located at the plain case half, is adjusted to adjust bearing preload. The single adjusting ring has the advantage of being able to set and adjust bearing preloads for both the first and second tapered roller bearings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A differential assembly10is installed within a carrier housing12as shown inFIG. 1. The differential assembly10cooperates with first and second axle shafts (not shown) as known to drive wheels of a drive axle. The differential assembly10is comprised of two case halves, a plug case half14and a plain case half16. The plug case half14and plain case half16are fixed together and provide a cavity18that receives a differential gear assembly20.

The differential gear assembly20includes a spider22that is fixed to the plain case half16. The spider can be comprised of three separate pins, or the spider could be formed as a single cross. Four differential gears24are supported on four legs of the spider22(only two are shown in the view ofFIG. 1). The differential gear assembly20also includes first and second side gears26that drive the first and second axle shafts, respectively. The operation of the differential gear assembly20to differentiate rotational speeds of the axle shafts under certain conditions is known and will not be discussed in further detail.

A first tapered roller bearing30is associated with the plug case half14and a second tapered roller bearing32is associated with the plain case half16. The first tapered roller bearing30is installed in an inverted position such that that an apex of the defining taper T1points towards the differential gear assembly20. The second tapered roller bearing32is installed in a non-inverted position such that an apex of the defining taper T2points in a direction away from the differential gear assembly20. This configuration of tapers T1, T2more evenly distributes gear loading and facilitates assembly and adjustment. This will be discussed in greater detail below.

The first tapered roller bearing30includes a first bearing cone34and a first bearing cup36. The first bearing cone34is fitted onto a bearing journal38of a trunnion40. The trunnion40is mounted to the carrier housing12. The first bearing cup36is mounted within an internal bore42of the plug case half14.

The second tapered roller bearing32includes a second bearing cone44and a second bearing cup46. The second bearing cone44is mounted on the plain case half16. The second bearing cup46is fitted on a bearing journal formed within a leg cap48. The leg cap48is mounted to the carrier housing12.

At least one shim50is mounted within the differential assembly10to adjust gear backlash. In the example shown, the shim50is mounted between an end of the first tapered roller bearing36and the plug case half14. Only one shim50may be required, or additional shims50could be added as needed, to set a desired backlash. The shims50could optionally be associated with the first tapered roller bearing cone34, and the trunnion40or shims50could be used with both the first tapered roller cup36and cone34.

A single adjusting ring60is used to set and/or adjust bearing preload. The adjusting ring60is positioned on a plain case side of the differential gear assembly20opposite from the plug case half14. The adjusting ring60is threaded or otherwise attached to the leg cap48and includes an abutment surface62that engages an end of the second tapered roller bearing cup46. Bearing preload is set and/or adjusted by rotating the adjusting ring60as known. The advantage with this configuration is that a single adjusting ring60can be used to adjust preload for both the first30and second32tapered roller bearings. Rotating the adjusting ring60against the second tapered roller bearing32adjusts the preload on the first30and second32tapered roller bearings via interaction with the plug case half14and plain case half16.

The plug case half14is shown in greater detail inFIGS. 2A and 2B, and the plain case half16is shown in greater detail inFIGS. 3A and 3B. A plurality of lubrication holes64is formed within the plug case half14to provide lubrication to the first tapered roller bearing30. Lubricant flows from the inside of a plug case half cavity to the first tapered roller bearing30through the lubrication holes64. This is necessary because the first tapered roller bearing30pumps lubricant from a small end to a large end of the taper. If the first tapered roller bearing30does not receive oil through this lubrication hole64, the small end may be starved of lubricant. The plug case half14includes the internal bore42with an inner circumferential surface68that receives the first bearing cup36. The plug case half14includes an outer circumferential surface70that is received within a cavity72formed within the plain case half16.

The cavity72of the plain case half16includes an inner circumferential surface74that abuts directly against the outer circumferential surface70of the plug case half14. The plain case half16includes a first outer circumferential portion76that defines an outer circumferential surface78. This outer circumferential surface78directly abuts against an inner circumferential surface80of a ring gear82(FIG. 1).

The ring gear82is driven by an input pinion (not shown), which receives driving input from a vehicle power source as known. The ring gear82includes a front side84with a plurality of ring gear teeth and a rear side86opposite from the front side84. The plain case half16includes a second outer circumferential portion88that abuts against an attachment feature90formed on the rear side86of the ring gear82.

The ring gear82, plug case half14, and the plain case half16are all fixed together as a unit. In the example shown, the plain case half16is welded to the ring gear82at the attachment feature90; and the plug case half14and plain case half16are welded together at an interface between the outer circumferential surface70of the plug case half14and the inner circumferential surface74of the plain case half16. It should be understood that while weld interfaces are shown, other attachment methods and/or fastening apparatuses could be used to secure the ring gear82, plug case half14, and the plain case half16together.

The trunnion40is shown in greater detail inFIG. 4. The trunnion40includes mounting ears98for attachment to the carrier housing12. The trunnion40also includes a first internal bore92for receiving one of the axle shafts and a second internal bore94that receives the through-shaft (not shown). The through-shaft transfers driving input to a rear-rear axle of a tandem drive axle as known. The trunnion40includes a tubular extension96that defines the bearing journal38that receives the first tapered roller bearing30.

This differential configuration facilitates assembly of the differential assembly10into the carrier housing12. As shown inFIGS. 5A-D, the first bearing cup36is installed within the inner bore42of the plug case half14and the second bearing cone44is installed on an outer circumferential surface of the plain case half16. This results in a bearing and differential case unit, as indicated at100. This unit100is rotated or swung through an opening102within the carrier housing12. The carrier housing12is configured such that a minimal clearance at104is required such that the plain case half16does not contact a wall portion106that partially defines the opening102.

As shown inFIGS. 5A-5D, the trunnion40is mounted to the carrier housing12and supports the first bearing cone34. The bearing and differential case unit100is swung into the opening102in the carrier housing12such that the first bearing cup36surrounds the first bearing cone34(seeFIGS. 5C-5D). The leg cap48, which is mounted to the carrier housing12, receives the second bearing cup46. When fully installed, the second bearing cup46surrounds the second bearing cone44(seeFIG. 5D).

The differential assembly10with the inverted bearing (first tapered roller bearing30) as described above, results in the effective center of the first tapered roller bearing30being located further away from the second tapered roller bearing32than in a traditional configuration. This effectively increases the bearing spread, which significantly lowers loading on the first tapered roller bearing30. As such, smaller, lower cost bearings can be used at this location. Loads on the bearing journal38are also lowered, such that lower cost materials and/or additional material processing steps are no longer required for the bearing journal38. Thus, a differential assembly10with the inverted bearing described above is easier to assemble and more evenly distributes gear loading, which results in improved durability and reduced cost.