Abstract:
A differential mechanism includes a housing portion having a generally annular wall with a generally annular inner surface. The annular wall defines an open end of the housing portion. The lid is affixed to the open end forming an enclosure with the housing portion. The opposing side bevel gears are in driving engagement with at least one bevel pinion assembly. The bevel pinion assembly includes at least one bevel pinion shaft with opposing axial ends, each supporting a side bevel gear. The bevel pinion assembly and the side bevel gears are disposed within said enclosure. The annular inner surface defines at least two receptors having ingress&#39;s, each receptorengaging one axial end of the pinion shaft independently of the lid.

Description:
[0001]    This invention relates generally to a differential mechanism for use with a vehicle transmission. This application claims priority to U.S. Provisional Patent Application Nos. 60/431,002 filed Dec. 5, 2002 and 60/512,001 filed Oct. 16, 2003. 
     
    
     
       BACKGROUND OF THE INVENTION  
       FIELD OF THE INVENTION  
         [0002]    Differential mechanisms are included in vehicle transmissions to transmit torque from a transmission output to opposing axle shafts allowing right and left wheels to rotate at different speeds, particularly important when negotiating a turn. While performing generally the same function, differential mechanisms have different dimensional requirements for rear wheel and front wheel drive vehicles. Specifically, differentials intended for use on front wheel drive vehicles require a beveled, and even annular shape in order to compensate for both the smaller packaging area available and to account for the steering characteristics of the front wheels of the vehicle. Rear wheel drive vehicles are typically larger and require more torque production than front wheel drive vehicles and include sport utility, pick-ups, and even heavy duty vehicles. Therefore, the rear wheel drive differential is typically dimensioned larger with heavier gauge steel than is a front wheel drive differential. Iron castings presently used to form the housing of a differential for a rear wheel drive vehicle requires a large number of machining operations to produce finished parts having the dimensions necessary to provide adequate tolerances to support the gears disposed within the housing. Dimensional accuracy is important to produce a vibration free motion of the differential in order to produce a smooth vehicle operation.  
           [0003]    Given the high torque requirements that is typical of the rear wheel drive vehicle, it is believed that the differential housing should include a more dimensionally stable and durable configuration than what is required of a front wheel drive differential housing. Furthermore, many of the manufacturing drawbacks of cast differential housings have resulted in excessive cost of a typical vehicle transmission. U.S. Pat. Nos. 6,045,479, 6,061,907, 6,176,152, and 6,379,277 each disclose a method of forming a differential housing using a cold flow-forming process. While the housing formed by the process disclosed in these prior references are believed to be effective for use in a front wheel drive transmission, it is believed that the housings will not be as effective for use in a rear wheel drive vehicle. However, the dimensional improvements produced by the cold flow-forming process that enable sheet steel to be used to form the differential housing can also be used to form a differential housing for a rear wheel drive differential. Therefore, the cold flow-forming process disclosed in these prior art patents are included by reference herein.  
           [0004]    Furthermore, improvements made to the cold, flow forming process and performance deficiencies of the prior art patents would also be desirable. For example, the prior art housings have not proven to withstand required durability testing due to the location of the shaft holding the pinion gears inside the housing. Specifically, sandwiching the shaft between two housing portions does not provide the durability required of a rear wheel drive differential.  
         SUMMARY OF THE INVENTION  
         [0005]    A differential mechanism includes a housing portion having a generally annular wall with a generally annular inner surface. The generally annular wall defines an open end of the housing portion. A lid is affixed to the open end forming an enclosure with the housing portion. Opposing side bevel gears are in driving engagement with at least one bevel pinion assembly, each being disposed within the enclosure. A bevel pinion shaft includes opposing axial ends, each of which supports a side bevel gear. The annular inner surface defines at least two receptors each rotatably engaging one axial end of the pinion shaft independent of and at spaced locations from the lid. The inner surface defines an ingress for each receptor for facilitate inserting the axial end of the shaft into the housing.  
           [0006]    The inventive configuration of the annular inner surface of the housing portion provides benefits not heretofore provided by prior art differential housings. Unlike differential housings formed from castings, the side bevel gears and the bevel pinion assembly can be inserted mechanically and do not require manipulation into openings typically disposed in cast differential housings. In fact, unlike cast differential housings, each bevel pinion assembly is pre-assembled prior to insertion into the differential housing. Still further, because the housing portion of the differential housing includes an annular wall, more than one bevel pinion assembly can be included in the differential mechanism, which can provide benefits such as, for example, increased torque. It is believed, that by adding two bevel pinion assemblies for a total of four pinion gears, the torque produced by a typical transmission is increased by 75%. A total of three bevel pinions is believed to increase the torque by around 40%. Still further, a housing portion having a generally annular wall is significantly stronger than a housing produced by a casting process, which includes large openings in order to insert each of the gears disposed within the housing. Therefore, the inventive differential mechanism includes a housing portion that is significantly stronger than a cast housing portion enabling a reduction in the gauge of steel used to form the differential housing reducing the mass of the differential housing by up to 10 pounds.  
           [0007]    Furthermore, spacing the assembly from the lid provides increased strength and housing durability over prior art devices because the assembly is spaced from the open end of the housing, unlike the prior art devices, which sandwich the assembly between two halves of the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0009]    [0009]FIGS. 1A and 1B is a side sectional view of the inventive differential housing of the present application;  
         [0010]    [0010]FIG. 2 is an exploded view of the inventive differential housing showing the bevel pinion assembly being inserted;  
         [0011]    [0011]FIG. 3 is an exploded view of an alternative embodiment of the inventive differential housing;  
         [0012]    [0012]FIG. 4 is a further alternate embodiment of the inventive differential housing;  
         [0013]    [0013]FIG. 5 is a further embodiment of the inventive differential housing showing an alternative lid with a planetary gear;  
         [0014]    [0014]FIGS. 6 a  and  6   b  are sectional views of alternative embodiments of the inventive differential housing showing localized, increased wall thickness;  
         [0015]    [0015]FIGS. 7A and 7B are a side, sectional views of an alternate embodiment of the differential housing having a splined inner surface on the housing and the lid;  
         [0016]    [0016]FIGS. 8A and 8B show a partial perspective view of the inventive differential housing showing a scoop; and  
         [0017]    [0017]FIG. 9 shows a top view of the differential housing showing the scoops. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring to FIG. 1, a differential assembly of the present invention is generally shown at  10 . A differential housing  12  includes a generally annual wall  14  that defines a generally annular inner surface  16 . The inner surface  16  defines at least two receptors  18 , and more preferably at least four receptors  18 , the purpose of which will be explained further below. The annular wall  14  of the differential housing  12  defines an open end  20 . The differential housing  12  defines a journal  22  at an opposite end of the housing  12  from the open end  20 . The journal  22  may be formed apart from the housing  12  and then welded to the housing assembly, or may be formed integrally with the housing  12 .  
         [0019]    The housing  12  is formed by a spin-forming or flow-forming cold working operation that is particularly suited to produce bowl-shaped parts, and more particularly suited to form rotatably symmetrical parts. The housing  12  is formed over a chuck (not shown) by spinning rollers (not shown) that are profiled. The spin forming is an operation in which the material is plasticized by a combination of compression and tension forces applied to a workpiece by rollers. Flow-forming is an operation in which deformation is the result of compression force applied by the rollers to the housing. Preferably, the housing  12  is pre-stamped from a heavy gauge steel and includes a general configuration of the chuck, however, the housing  12  may be formed from a flat panel if necessary. With either process, precise dimensional tolerances can be maintained on the inner surface of a workpiece in which a net shape is produced with the additional step of machining the inner surface as is required of a cast housing. A near net forged or cast preform may also be used and the net shapes formed over the chuck in the same manner a detailed above.  
         [0020]    During the forming operation, the housing  12  is plasticized which minimizes spring back and allows a high level of dimensional accuracy. The outer contour of the chuck is imprinted very precisely into the inner surface of the housing  12 . The outer surface of the housing  12  is only free-formed by spinning rollers. Therefore, the outer surface may have a wavy shape, which does not adversely affect the operation of the differential assembly  10 .  
         [0021]    In the case of spin-forming in general there is no deliberate change in the wall thickness during the forming process. The starting workpiece is a sheet metal disc. Preferably, the sheet metal disc is not entirely bake-hardened in order to facilitate the formation of the housing  12 . However, it may be desirable to bake-harden the surface of the sheet metal while not bake-hardening the inner thickness of the sheet metal.  
         [0022]    In the case of flow-forming, there is a deliberate change in the wall thickness of the housing  12  to that of the preformed part. Locally increasing the wall thickness is helpful toward strengthening and stiffening the housing  12  as required by its operational loading and material properties as will be explained further below. The starting housing stamping is typically a tube or cup, which is parallel sided or tapered. The preformed part is clamped against a spinning chuck, which is driven by a spindle. One or more spinning rollers apply radial force into the surface of the preform until the inner surfaces of the workpiece conforms to the external surfaces of the spinning chuck and acquires the required shape and dimensions. The process is known to produce excellent internal dimensional accuracy and internal surface finish while still being able to create integrated profiles and features such as, for example, the receptors  18 . The rollers force the sheet metal inwardly toward the chuck, which includes projections that match the preferred dimension of the receptors thereby forming the receptors in the annular wall  14  of the differential housing  12 . A chuck having collapsing inserts to form, for example, the receptors  18 , is required to meet various design characteristics that protrude during the forming operation and retract into the chuck to remove the housing  12  from the chuck.  
         [0023]    A lid  24 , preferably formed as a stamping by a die press, is affixed to the open end  20  of the differential housing  12  via a laser weld bead  26 . A welding laser follows a seam formed between the differential housing  12  and the lid  24  to secure the lid  24  to the differential housing  12 .  
         [0024]    The lid  24  includes a lid journal  28  defining a common axis with an axis defined by the housing journal  22 , the purpose of which will be more evident when described further below. Each journal  22 ,  28  is sized to receive a splined shaft (not shown) that transfers motion to the vehicle wheels (not shown).  
         [0025]    The differential housing  12  and the lid  24  define an enclosure  30  in which opposing side bevel gears  32  are disposed. The side bevel gears  32  are in driving engagement with at least one bevel pinion assembly  34 . Each bevel pinion assembly includes a bevel pinion shaft  36  having opposing axial ends  38 . A pinion gear  40  is disposed near each opposing axial end  38  on the bevel pinion shaft  36 . Each opposing axial end  38  is pivotally received by a receptor  18  thereby allowing the pinion gears  40  to pivot upon an axis defined by the opposing receptors  18 . Each axial end  38  of the pinion shaft  36  is received by a receptor  18  in a locking engagement so that the shaft  36  does not pivot relative to the receptors  18  thereby ensuring that the pinion gears  40  rotate upon the shaft  36 . For example, the axial end is formed to define flat surfaces that about cooperative flat surfaces defined by the receptors  18 . Alternatively, the axial ends  38  are welded to the receptors  18  to prevent shaft  36  rotation.  
         [0026]    Each side bevel gear  32  includes splines  42  to receive the splined shaft and have a common axis with the housing journal  22  and the lid journal  28 . The bevel pinion assembly  34  and the side bevel gears  32  are in driving engagement as is known to those of skill in the art of vehicle transmissions. A second shaft  44  is optionally inserted through, or otherwise affixed to, a bevel pinion shaft in order to include a second bevel pinion assembly  34  in the enclosure  30 . The second shaft  44  rotates relative to the first shaft  36 . It is believed that the addition of a second bevel pinion assembly  34  providing a total of four pinion gears  40  will produce 75% more torque than what is available with a single bevel pinion assembly  34 . Additionally, providing a total of three pinion gears are believed to produce 40% additional torque. Cast differential housings presently available do not provide the ability to include a second bevel pinion shaft due to the large opening in the annular wall required to insert the single bevel pinion assembly. The second bevel pinion assembly is not shown in FIG. 1 in order to provide clarity to the inventive concepts.  
         [0027]    A ring gear  46  is affixed to the open end  20  of the differential housing  12 . The ring gear  46  is preferably attached to the differential housing  12  by laser-welding, which produces a ring gear laser weld bead  48  at the seam formed between the differential housing  12  and the ring gear  46 . Preferably, the ring gear  46  overlays the laser weld beam  26  formed at the seam between the lid  24  and the open end  20  of the differential housing  12 . Alternatively, as shown in FIG. 1 a, a ring gear  46   a  is formed integrally with the lid  24   a  to eliminate the step of welding the ring gear  24   a  to the housing  12 .  
         [0028]    [0028]FIG. 2 shows an exploded view of the inventive differential assembly  10  during the assembly process. In order to align the bevel pinion shaft  36  so that the opposing axial ends  38  are pivotally retained in the receptors  18 , each receptor  18  includes a beveled edge  50  providing an ingress to the receptors  18  and allowing for the angled insertion of the bevel pinion assembly  34  into the differential housing  12 . It is believed that the angle of ingress of the bevel edge  50  would need to be adjusted for the installation of a bevel pinion assembly  34  having four or more pinion gears  40 . During the assembly process, a first side bevel gear  32  is inserted into the differential housing  12  aligning the splines  42  with the housing journal  22 . Once the side bevel gear  32  is in place, the bevel pinion assembly  34  is inserted so that the bevel pinion shaft  36  is pivotally retained by the receptors  18  as stated above. After the bevel pinion assembly  34  is inserted into the differential housing  12 , the second side bevel gear  32  is inserted into the differential housing  12  in driving engagement with the pinion gears  40 . Once all the gears  32 ,  40  are in place, the lid  24  is placed over the open end  20  of the differential housing  12 . The seam formed between the differential housing  12  and the lid  24  is preferably laser-welded securing the lid  24  to the differential housing  12  so that the lid journal  28  is axially aligned with the spines  42 . Other methods of securing the lid  24  to the housing  12  may also be used.  
         [0029]    [0029]FIG. 3 shows an alternative embodiment of the differential housing  52  and the method of assembly. The method of assembly represented in FIG. 3 is preferred when four or more pinion gears  40  are included in the assembly  10 . The alternate differential housing  52  includes an inner surface  54  of an annular wall  56  having a diameter that is generally as wide as the bevel pinion shaft  36 . The alternate inner surface  54  may include a bevel edge  50  providing an ingress to the receptors  18 . However, it should be understood by those of skill in the art of vehicle transmissions that the diameter of the alternate inner surface  54  can be optimized so that a bevel edge  50  would not be required. Once the gears  32 ,  40  are positioned in the differential housing  12 , the lid  24  is positioned over the open end  20  of the differential housing  12 . A subsequent rolling process in the direction of arrows  58  reforms the open end  20  of the differential housing  12  thereby reducing the diameter of the alternate inner surface  54 . Subsequently, the seam formed between the lid  24  and the differential housing  52  is laser-welded thereby securing the lid  24  to the alternate differential housing  52 . The final dimensions of the alternate differential housing  52 , after the additional rolling step, is identical to the first embodiment of the differential housing  12 .  
         [0030]    A further alternate embodiment of a differential housing  60  is shown in FIG. 4. An alternate annular wall  62  includes an alternate inner surface  64 . At least two receptor slots  66  provide an ingress for the opposing axial ends  38  of the bevel pinion shaft  36  during assembly. The tension transferred to the side bevel gears  32  from the shafts engaging the splines  42  holds the bevel pinion assembly  34  in a fixed location once the assembly of the differential assembly  10  is complete. The slots  66  are preferable when a bevel pinion assembly  34  having at least four pinion gears  40  is included. As stated above, once all the gears  32 ,  40  are in place, the lid  24  is positioned over the open end  20  of the differential housing  12  and the seam formed between the differential housing  12  and the lid  24  is laser-welded securing the lid  24  to the differential housing  12 . As stated above, once the lid  24  is laser-welded to the open end  20  of the differential housing  12 , the ring gear  46  is laser-welded to the differential housing  12  over the lid  28  as shown in FIG. 1.  
         [0031]    [0031]FIG. 5 shows a further alternate embodiment of the inventive differential assembly  10  where the ring gear  46  has been replaced by planetary carriers  68 . The planetary carriers  68  are desirable in more sophisticated transmission assemblies preferred on luxury vehicles due to the smoother transition between gears that is produced by the planetary carriers  68 . FIG. 5 shows a planetary gear assembly  70  having an outer end plate  72  and an inner end plate  74  mated with opposing side plates  76  to support planetary gears  68 . Each of the plates  72 ,  74 ,  76  are preferably laser-welded together and the assembly  70  is laser-welded to the differential housing  12  during the assembly process. Different plate configurations can be used as desired to support the planetary gears  68  upon the differential housing  12  as may be required by operational or dimensional requirements.  
         [0032]    Referring now to FIG. 6A, a still further embodiment of the inventive differential assembly is generally shown at  78 . In this embodiment, a differential housing  80  defines an annular wall  82  into which a protuberance  84  is locally formed. Preferably, the protuberance  84  takes the form of an annular bead that encircles the entirety of the annular wall  82 . The protuberance  84  increases the thickness of the annular wall  82  at the location of each receptor  86 . The increased wall thickness at each receptor  86  increases the strength of the generally annular wall  84  improving the durability of the housing  80  during operation of a motor vehicle. It should be understood that the protuberance  84  may also be locally formed proximate each receptor  86  as desired.  
         [0033]    [0033]FIG. 6B shows still a further embodiment where a flange  88  is formed around each receptor  86  on an outside surface of the generally annular wall  82 . The flange  88  also improves the durability of the housing  80  during operation of the motor vehicle. The flange  88  may define an opening  90  into the receptor  86  and therefore into the enclosure  30  of the housing  80 . The flange  88  may be formed during the cold forming process or during a subsequent manufacturing operation performed on the housing  80 .  
         [0034]    A still further embodiment of the invention as generally shown at  92  in FIG. 7A. In this embodiment, a spline portion  98  is formed in the inner surface  94  of the generally annular wall  96 . The spline portion  98  is adapted to receive clutch plates (not shown) known to those of skill in the art to provide enhanced gear shifting properties to the transmission. The splines  98  are formed from the chuck during the cold forming process described above. The splines  98  and the clutch plates provide a clutch activated gear shift that enhances the shifting properties of the transmission. It is desirable to form a second set of splines  99  in the inner surface  94  of the annular wall  96  at an opposite end of the housing  12  as shown in FIG. 7A. Alternatively, the second set of splines  99  are formed in the lid  28 , which is received by the housing  12  as is shown in FIG. 7B.  
         [0035]    As is known to those of skill in the art, lubricant flows throughout a transmission to facilitate the operation of the transmission gears. It is desirable to provide a free flow of the transmission fluid inside the differential housing  12 . As shown in FIGS. 8 and 9A, an inlet scoop  100  is disposed in an outer wall  102  of the differential housing  12 . Preferably, the annular wall  14  is pierced and the scoop is formed by forcing the annular wall  14  outwardly at the location of the pierce forming an first opening  102  in the generally annular wall  14 . Preferably, the first opening  102  faces in the direction of the rotating housing  12  so that transmission fluid is forced into the enclosure  30  during operation of the vehicle. A second scoop opening  104  is formed on an opposite side of the housing  12  of the first scoop opening  102  to provide additional lubricant to continuously flow through the enclosure  30  during operation of the motor vehicle. Preferably, the scoop openings  100 ,  104  are spaced between the receptors  18 ,  86  best seen in FIGS. 1 through 7. Alternatively, the scoops  100  are located proximate the splines  98  on the inner surface  16  of the housing  12  as shown in FIG. 9B. The lubricant entering the enclosure  30  through scoop openings exits through at least one of the journals  22 ,  28  providing additional lubrication to the shafts extending into the enclosure  30  through the journals  22 ,  28 .  
         [0036]    The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.  
         [0037]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.