Patent Publication Number: US-2013252776-A1

Title: Differential

Description:
TECHNICAL FIELD 
     The present invention relates to a differential. 
     BACKGROUND ART 
     JP2010-121641A and JP1996-49758A disclose a differential. The differential is configured, for example, as shown in  FIG. 3 . A drive gear  50  is driven by a propeller shaft. The drive gear  50  is rotatably supported on a carrier case  51  via a bearing. A pilot bearing  52  supports a tip portion of the drive gear  50 . A ring gear  53  is engaged with the drive gear  50 . 
     The ring gear  53  is attached to a differential case  55 . A central portion of the differential case  55  is bag-shaped and pinion gears  56  and side gears  57   a,    57   b  to be described later are housed inside this central portion. The differential case  55  is rotatably supported on the carrier case  51  via bearings  58   a,    58   b.    
     The left side gear  57   a  integrally rotates with a left axle shaft. The right side gear  57   b  integrally rotates with a right axle shaft. The pinion gears  56  are engaged with each side gear  57   a,    57   b  and are attached to the differential case  55  via a spider shaft  59 . The spider shaft  59  is formed by connecting four shaft portions in a crisscross manner. Each shaft portion of the spider shaft  59  rotatably supports the pinion gear  56 . 
     The rotation of the drive gear  50  is transmitted to the differential case  55  via the ring gear  53  and the pinion gears  56  revolve with the rotation of the differential case  55 . When the pinion gears  56  revolve, the left and right axle shafts rotate together with the respective side gears  57   a,    57   b.  If there is a difference in rotational resistance (load) between the left and right axle shafts, each pinion gears  56  rotates according to the rotational resistance. In this way, the rotation speed of the axle shaft on a low-load side increases while that of the axle shaft on a high-load side decreases. 
     SUMMARY OF THE INVENTION 
     Since the side gears  57   a,    57   b  and the pinion gears  56  are housed in the bag-shaped portion (central portion) of the differential case  55  in the above differential, there is a possibility that the supply of lubricant (this is, for example, scooped up by the drive gear) becomes insufficient. This may possibly make it difficult to ensure lubrication performance of each sliding portion and cause seizure of each sliding portion. 
     The present invention aims to improve lubrication performance of a differential. 
     According to one aspect of the present invention, a differential is provided which comprises a ring gear which is engaged with a drive gear, a differential case which integrally rotates with the ring gear, axle shafts which are coaxially arranged on left and right sides, a side gear which integrally rotates with the left axle shaft and a side gear which integrally rotates with the right axle shaft, a pinion gear which is engaged with each side gear, a spider shaft which rotatably supports the pinion gear on the differential case, and a carrier case which rotatably supports the drive gear, wherein the carrier case rotatably supports each side gear and the left axle shaft or the right axle shaft rotatably supports the spider shaft of the differential case. 
     Embodiments of the present invention and advantages thereof are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view showing a differential according to an embodiment of the present invention. 
         FIG. 2  is a view showing rotation transmission paths of the differential according to the embodiment of the present invention. 
         FIG. 3  is a sectional view showing a conventional differential. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     In  FIGS. 1 and 2 , a drive gear  10  is driven by a propeller shaft. The drive gear  10  is rotatably supported on a carrier case  11  via bearings  12   a,    12   b.  The bearing  12   a  supports a shaft (drive shaft coupled to the propeller shaft) of the drive gear  10 . The pilot bearing  12   b  supports a tip portion of the drive gear  10 . A ring gear  13  is engaged with the drive gear  10 . A final speed reduction ratio is set based on the number of teeth of the drive gear  10  and that of teeth of the ring gear  13 . 
     The ring gear  13  is attached to a differential case  15 . A spider shaft  16  is provided in the differential case  15 . The spider shaft  16  is formed by connecting four shaft portions in a crisscross manner. Each shaft portion of the spider shaft  16  rotatably supports a pinion gear  17 . 
     Side gears  18   a,    18   b  are engaged with the pinion gears  17  and coaxially arranged at the left and right sides of the pinion gears  17 . The side gears  18   a,    18   b  are rotatably supported on the carrier case  11  respectively via bearings  19   a,    19   b.  The left side gear  18   a  integrally rotates with a left axle shaft  20   a.  The right side gear  18   b  integrally rotates with a right axle shaft  20   b.    
     Each side gear  18   a,    18   b  includes a spline hole  21   a,    21   b  with a spline groove engaged with a spline groove of the axle shaft  20   a,    20   b.  The side gear  18   a,    18   b  further includes a through hole  22   a,    22   b  which is open on the same axis as the spline hole  21   a,    2  lb. One axle shaft  20   a  includes a shaft portion  24  (extension shaft) coaxially extending toward the axle shaft  20   b.  The extension shaft  24  rotatably supports the spider shaft  16  and rotatably supports the side gear  18   b  that integrally rotates with the right axle shaft  20   b.    
     The side gears  18   a,    18   b  and the axle shafts  20   a,    20   b  are spline-connected to be integrally rotatable about an axis and displaceable in an axial direction. The spider shaft  16  and the side gears  18   a,    18   b  are displaceable in the axial direction on the extension shaft  24  rotatably supporting these. 
     Steps  30  for locking inner races of the bearings  19   a,    19   b  are formed on the outer peripheries of the side gears  18   a,    18   b.  Outer races of the bearings  19   a,    19   b  are engaged with the carrier case  11  to be displaceable in the axial direction. Adjuster nuts  31   a,    31   b  can fix the bearings  19   a,    19   b  and the side gears  18   a,    18   b  at predetermined positions by fastening the outer races of the bearings  19   a,    19   b  from opposite sides of a differential gear. 
     As shown in  FIG. 2 , the rotation of the drive gear  10  is transmitted to the differential case  15  via the ring gear  13  and the pinion gears  17  revolve with the rotation of the differential case  15 . When the pinion gears  17  revolve, the left and right axle shafts  20   a,    20   b  rotate together with the respective side gears  18   a,    18   b.  If there is a difference in rotational resistance (load) between the left and right axle shafts  20   a,    20   b,  each pinion gear  17  rotates. In this way, the rotation speed of the axle shaft on a low-load side increases while that of the axle shaft on a high-load side decreases. Arrows of  FIG. 2  indicate transmission paths of rotational forces associated with the revolution of the pinion gears  17 . 
     Since each side gear  18   a,    18   b  is supported on the carrier case  11  instead of being assembled with the differential case  15 , a structure for rotatably supporting each side gear  18   a,    18   b  can be omitted from the differential case  15 . 
     The differential case  15  is composed of a central portion  15   a  supporting the spider shaft  16  and a peripheral edge portion  15   b  forming a mounting portion for the ring gear  13  and so formed that opposite sides of the central portion  15   a  are widely open. That is, as compared with the conventional differential case  55  (see  FIG. 3 ), a part which rotatably supports the side gears  57   a,    57   b  by covering the side gears  57   a,    57   b  on the opposite sides and is supported on the carrier case  51  via the bearings  58   a,    58   b  is omitted. 
     Thus, the side gears  18   a,    18   b  and the pinion gears  17  are exposed from the differential case  15  and more easily come into contact with lubricant scooped up by the drive gear  10 , wherefore lubrication performance of the differential can be improved. Further, the differential case  15  can be made smaller in size and lighter in weight. 
     Although the differential case  15  is not supported on the carrier case  11 , necessary support performance can be ensured since the differential case  15  is rotatably supported on the extension shaft  24  of the axle shaft  20   a  via the spider shaft  16 . Further, since not only the left side gear  18   a,  but also the right side gear  18   b  is supported by the extension shaft  24 , support performance of the entire differential gear can be sufficiently improved. 
     Since the differential case  15  and the side gears  18   a,    18   b  are displaceable in the axial direction in this embodiment, an adjustment of a mounting distance M made in association with a change in the final speed reduction ratio can be easily dealt with without exchanging the differential case  15 . Specifically, the adjustment of the mounting distance M associated with a change in the final speed reduction ratio can be made by loosening the adjuster nuts  31   a,    31   b  and displacing the differential case  15  and the side gears  18   a,    18   b  in the axial direction. 
     The embodiments of the present invention described above are merely illustration of some application examples of the present invention and not of the nature to limit the technical scope of the present invention to the specific constructions of the above embodiments. 
     For example, although the extension shaft  24  rotatably supports the side gear  18   b  engaged with the axle shaft  20   b  on the opposite side, this part may be omitted. 
     The present application claims a priority based on Japanese Patent Application No. 2010-276105 filed with the Japan Patent Office on Dec. 10, 2010, all the contents of which are hereby incorporated by reference. 
     INDUSTRIAL APPLICABILITY 
     This invention can be applied to differentials of various machines without being limited to application to vehicle differentials.