Abstract:
A travel assembly is provided with a cylindrical spindle for being fixed on a body of a working vehicle, a rotary shaft arranged extending in an axial direction through the spindle and rotationally drivable by a driving source, a rim rotatably arranged on a side of an outer periphery of the spindle to permit mounting of a wheel thereon, a planetary gear reduction mechanism for transmitting rotation of the rotary shaft to the rim at a reduced speed, a bearing rotatably supporting the rotary shaft via a sleeve integrally fitted on the rotary shaft, and a retainer holding the bearing in place. A lube oil pipe for feeding lube oil to the rotary shaft is held in place by the retainer. The lube oil pipe branches within the retainer to form an oil passage. The oil passage has an opening through which the lube oil can be fed to rolling elements in the bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of Japanese Patent Application 2008-289860 filed Nov. 12, 2008, which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to a travel assembly, which is to be arranged on a wheeled working vehicle such as a dump truck for transporting, for example, crushed rocks dug in a mine or the like, and has a travel motor and a planetary gear reduction mechanism for transmitting rotation of a rotary shaft of the travel motor to a wheel at a reduced speed. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, drive assemblies for driving drive wheels of a wheeled working vehicle, for example, a dump truck to travel are each provided with a cylindrical spindle to be mounted on a vehicle body, a rotary shaft arranged extending in an axial direction through the spindle and rotationally drivable by a driving source such as an electric motor, a rim rotatably arranged on an outer periphery of a free end portion of the spindle via a bearing to permit mounting of a wheel on the rim, and a multiple-stage, planetary gear reduction mechanism for transmitting rotation of the rotary shaft to the rim at a reduced speed. 
         [0006]    The planetary gear reduction mechanism transmits a rotation output from the driving source composed, for example, of the electric motor to the wheel via the rim at a reduced speed, so that a rotary torque is produced at the drive wheel of the vehicle, such as a front wheel or rear wheel, to cause the dump truck to travel. 
         [0007]    In a conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, two sets of planetary gear reduction mechanisms are included for increasing rotary torque in a vehicle and composed of a sun gear, plural planet gears, a ring gear, a carrier, and the like, respectively. Each planetary gear reduction mechanism is constructed such that the carrier rotatably supports the plural planet gears, which are rotatable in accordance with rotation of the sun gear, via plural support pins and rotation of the respective planet gears are transmitted to the ring gear and are outputted as a rotation output to an outside. On the other hand, the rotary shaft is rotatably supported by a bearing arranged at an intermediate location in a longitudinal direction from a motor to the planetary gear reduction mechanism. 
         [0008]    In the conventional technology disclosed in the above-mentioned U.S. Patent Application Publication No. 2004/0065169 A1, however, large rotational loads are applied to each travel assembly in such a dump truck, and therefore, it is necessary to feed lube oil to the rotary shaft and bearing to maintain them under lubrication. 
         [0009]    In the above-described construction, however, holding of a great deal of lube oil within the travel assembly results in energy loss and heat production due to resistance to agitation of the lube oil as a result of rotation of the respective gears. It is, therefore, common to set the quantity of lube oil, which is to be held within the travel assembly, at a minimum need (for example, approximately from ⅕ to ⅓ of the internal capacity). When set so, the oil level is located on a side lower than the rotary shaft so that only the planet gears and the carrier supporting the planet gears thereon are immersed in the lube oil and the rotary shaft and its bearing remain free from immersion in the lube oil. 
         [0010]    In the conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, the bearing that rotatably supports the rotary shaft thereon is arranged in proximity to the planet gears in expectation of lubrication with lube oil mist splashed as a result of rotation of the planet gears. 
         [0011]    The conventional technology disclosed in U.S. Patent Application Publication No. 2004/0065169 A1, however, involves a potential problem that the lube oil may not be fed in any sufficient quantity to the bearing for the rotary shaft because the lube oil for lubricating the bearing, which rotatably supports the rotary shaft thereon, is fed only by a method that relies upon dispersion of lube oil mist as a result of splashing of the lube oil by rotation of the planet gears. A failure to feed the lube oil in a sufficient quantity is accompanied by a problem that the bearing is reduced in durability and service life. 
       SUMMARY OF THE INVENTION 
       [0012]    With the above-mentioned problem of the conventional technology in view, the present invention has as an object thereof the provision of a travel assembly that can feed a sufficient quantity of lube oil to a bearing for a rotary shaft. 
         [0013]    To achieve the above-described object, the present invention provides, in one aspect thereof, a travel assembly provided with a cylindrical spindle for being fixed on a body of a working vehicle, a rotary shaft arranged extending in an axial direction through the spindle and rotationally drivable by a driving source, a rim rotatably arranged on a side of an outer periphery of the spindle to permit mounting of a wheel thereon, a planetary gear reduction mechanism for transmitting rotation of the rotary shaft to the rim at a reduced speed, a bearing rotatably supporting the rotary shaft via a sleeve integrally fitted on the rotary shaft, and a retainer holding the bearing in place, wherein a lube oil pipe for feeding lube oil to the rotary shaft is held in place by the retainer, the lube oil pipe branches within the retainer to form an oil passage, and the oil passage has an opening through which the lube oil can be fed to rolling elements in the bearing. 
         [0014]    In the present invention constituted as described above, within the retainer that holds in place the bearing with the rotary shaft rotatably supported thereon and that also holds in place the lube oil pipe through which the lube oil is forced to circulate, the lube oil is fed to the oil passage formed by branching the lube oil pipe and is then fed through a shortest distance from the opening of the oil passage to the rolling elements in the bearing for the rotary shaft. The bearing can, therefore, be improved in durability and service life by surely feeding a sufficient quantity of the lube oil to the rolling elements in the bearing as described above. 
         [0015]    In the travel assembly according to the present invention, the retainer and sleeve may preferably be provided, on a side of the driving source, with flange portions, respectively, and the flange portions may preferably extend opposite each other such that the flange portions shield the rolling elements in the bearing. According to the present invention constituted as described above, a gap between the retainer and the sleeve can be reduced compared with an embodiment not provided with such flange portions, and therefore, the lube oil fed through the opening of the oil passage can be restrained from flowing out past the rolling elements and reaching the motor. Accordingly, it is possible to avoid contamination of motor oil. 
         [0016]    In the travel assembly according to the present invention, the oil passage may preferably have, on a side of the rolling elements in the bearing, the opening in the flange portion arranged on the retainer. Different from an embodiment in which the opening of such an oil passage is not arranged in the flange portion arranged on the retainer, in other words, an embodiment in which the bearing is provided with such an opening, the present invention constituted as described above does not require machining that would otherwise be needed to form such an oil passage in the bearing, and therefore, can use a general-purpose bearing as the bearing. 
         [0017]    In the travel assembly according to the present invention, the flange portions of the retainer and sleeve may preferably overlap with each other at end portions thereof. In the present invention constituted as described above, the gap between the retainer and the sleeve takes a labyrinth form. The lube oil fed through the opening of the oil passage can, therefore, be prevented from flowing out past the rolling elements and reaching the motor. Accordingly, it is possible to surely avoid contamination of motor oil. 
         [0018]    In the travel assembly according to the present invention, the oil passage may preferably comprise a through-hole extending from an outer periphery of the retainer to an inner periphery of the retainer, intersecting with the lube oil pipe, and being closed up at an opening thereof on a side of the outer periphery of the retainer. According to the present invention constituted as described above, hole drilling is feasible from the outer periphery of the retainer, and therefore, the manufacture is easy compared with an embodiment in which such an oil passage is formed by hole drilling from an inner periphery of an annular retainer to a location where the oil passage intersects with the lube oil pipe. 
         [0019]    In the travel assembly provided with the bearing rotatably supporting thereon the rotary shaft rotationally drivable by the driving source and also with the retainer holding the bearing in place, the lube oil pipe for feeding lube oil to the rotary shaft is held in place by the retainer, and the oil passage branching out from the lube oil pipe within the retainer has the opening through which lube oil can be fed through a shortest distance to the rolling elements in the bearing. Therefore, the present invention can surely feed a sufficient quantity of the lube oil to the rolling elements in the bearing. As a consequence, fresh lube oil can be continuously fed to the rolling elements in the bearing, and therefore, the bearing, that is, the travel assembly can be provided with durability and service life improved over those of the conventional technology. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a side view showing a dump truck equipped with travel assemblies according to a first embodiment of the present invention. 
           [0021]      FIG. 2  is a rear view of the dump truck shown in  FIG. 1 . 
           [0022]      FIG. 3  is a fragmentary cross-sectional view illustrating one of the travel assemblies according to the first embodiment of the present invention. 
           [0023]      FIG. 4  is an enlarged cross-sectional view taken in a direction of arrow IV of  FIG. 3 . 
           [0024]      FIG. 5  is a fragmentary, side cross-sectional view corresponding to  FIG. 4 , and depicts a supporting bearing section. 
           [0025]      FIG. 6  is a fragmentary, side cross-sectional view similar to  FIG. 5 , and shows a travel assembly according to a second embodiment of the present invention. 
           [0026]      FIG. 7  is a fragmentary, side cross-sectional view similar to  FIG. 5 , and depicts a travel assembly according to a third embodiment of the present invention. 
           [0027]      FIG. 8  is a fragmentary, side cross-sectional view similar to  FIG. 5 , and illustrates a travel assembly according to a fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    Best embodiments for practicing the travel assembly according to the present invention will hereinafter be described based on the accompanying drawings. 
       First Embodiment 
       [0029]    Referring first to  FIGS. 1 through 5 , a travel assembly according to a first embodiment of the present invention will be described. 
         [0030]    As shown in  FIGS. 1 and 2 , a wheeled vehicle on which travel assemblies according to a first embodiment of the present invention are arranged, for example, a mining dump truck is provided with a frame structure chassis  1 , a vessel  2  tiltably mounted as a load body on the chassis  1 , a cab  3  arranged on a front side of the chassis  1 , and plural wheels  5 . As illustrated in  FIG. 2 , a travel assembly  4  according to the first embodiment is arranged on a rear part of the chassis  1 , and rotationally drives a rear wheel out of the wheels  5 . 
         [0031]    As depicted in  FIG. 3 , the travel assembly  4  according to the first embodiment is provided with an electric motor  6  as a driving source and a cylindrical spindle  7  that fixedly secures the electric motor  6  on the chassis  1  shown in  FIGS. 1 and 2 . A sun gear  9  is arranged on a free end portion of a rotary shaft  8  of the electric motor  6 , and a bearing  22  is arranged corresponding to a substantially central portion of the rotary shaft  8 . The bearing  22  is supported on the spindle  7  by a retainer  21 . The travel assembly  4  is also provided with a suction-side lube oil pipe  24  and a delivery-side lube oil pipe  25 , which serve to circulate lube oil  26  held in the travel assembly  4 . The travel assembly  4  is further provided with a carrier  11  rotatably supporting the planet gears  10  thereon, a sun gear  14  integrated via a gear coupling  13  with a ring gear  12  meshing with the planet gears  10 , planet gears  15  meshing with the sun gear  14 , and a carrier  16  rotatably supporting the planet gears  15  thereon. The travel assembly  4  is still further provided with a drum  18  to which rotation of the electric motor  6  is finally transmitted, and rims  20  carrying tires of the wheel  5  integrally mounted thereon and fixedly secured on the drum  18  via a spacer  19 . 
         [0032]    In the travel assembly  4  according to the first embodiment, the rotary shaft  8  is rotatably supported on the bearing  22  via a sleeve  23  fitted on the rotary shaft  8  as shown in  FIG. 4 . The suction-side lube oil pipe  24  and delivery-side lube oil pipe  25  are fixed on the retainer  21  by flanges  28 , respectively. 
         [0033]    In the travel assembly  4  according to the first embodiment, the bearing  22  is composed of rolling elements  31 , an inner race  32  and an outer race  33  as shown in  FIG. 5 . The outer race  33  that holds these rolling elements  31  in place is supported by the retainer  21 . Further, the sleeve  23  is fixed relative to the inner race  32  of the bearing  22  by an anti-rotation washer  27  and an unillustrated nut. 
         [0034]    In this first embodiment, an oil passage  30  is arranged, as illustrated in  FIG. 5 , by arranging a through-hole in the retainer  21  and outer race  33  such that the through-hole intersects with the delivery-side lube oil pipe  25 , and an opening of the oil passage  30 , said opening being on a side of an outer periphery of the retainer  21 , is closed up by a plug  29 . In other words, the oil passage  30  branches out from the delivery-side lube oil pipe  25  within the retainer  21 , and has an opening through which lube oil can be fed to the rolling elements  31  in the bearing  22 . 
         [0035]    In the first embodiment constituted as described above, the electric motor  6  drives the sun gear  9  by way of the rotary shaft  8 . The sun gear  9  then drives the planet gears  10 , and their driving power is transmitted to the ring gear  12  and then drives the sun gear  14  and planet gears  15  via the gear coupling  13 . The planet gears  15  drive a ring gear  17 , and its driving power is transmitted to the wheels  5  via the drum  18  and spacer  19 . As has been described above, the rotation of the electric motor  6  is reduced in speed but is increased in torque by the sun gears  9 , 14 , planet gears  10 , 15  and ring gears  12 , 17 , and by rotation of the wheels  5  which have acquired the resulting large torque, the dump truck is allowed to travel. 
         [0036]    In the travel assembly  4  according to the first embodiment, the lube oil  26  held in the travel assembly  4  is circulated through the suction-side lube oil pipe  24  and delivery-side lube oil pipe  25  as mentioned above. The circulation is forcedly performed by an unillustrated pump, and a portion of the lube oil  26  is fed to the bearing  22  through the oil passage  30  branching out from the delivery-side lube oil pipe  25 . 
         [0037]    It is to be noted that, because the oil passage  30  is also formed in the outer race  33  of the bearing  22 , the lube oil  26  is surely fed over a shortest distance to the rolling elements  31  in the bearing  22  and lubricates the rolling elements  31 . Subsequently, the lube oil  26  is discharged through clearances between the rolling elements  31  and the inner race  32  and outer race  33 , and is again drawn and circulated through the suction-side lube oil pipe  24 . 
         [0038]    According to the first embodiment constituted as described above, the bearing  22  can be arranged corresponding to a substantially central portion of the rotary shaft  8 , at which decentering of the rotary shaft  8  becomes greatest, and therefore, the rotational speed that permits safe rotation can be increased. In addition, the oil passage  30  branches out within the retainer  21  at a location just proximal to the bearing  22 . It is, therefore, possible to surely feed a sufficient quantity of the lube oil  26  to the rolling elements  31  in the bearing  22  through a shortest distance via the opening of the oil passage  30  and to provide the bearing  22  with improved lubricity and hence with improved durability and service life. 
         [0039]    Further, the retainer  21  is an annular member. Although machining can be applied to form the oil passage  30  only from a side of its inner periphery to the location at which the oil passage  30  branches out from the delivery-side lube oil pipe  25 , hole drilling from the side of the inner periphery of the retainer  21  toward its outer periphery requires a special tool, and therefore, incurs an increase in machining cost. According to the first embodiment, hole drilling is easy owing to the adoption of the structure that a through-hole is formed by hole drilling from the side of the outer periphery of the retainer  21  and is then closed up by the plug  29  on the side of the outer periphery of the retainer  21 . 
       Second Embodiment 
       [0040]    Referring next to  FIG. 6 , a travel assembly according to a second embodiment of the present invention will be described. 
         [0041]    In this second embodiment, a retainer  21 A and a sleeve  23 A are provided, on a side of the electric motor  6 , with a retainer-side flange portion  34  and a sleeve-side flange portion  35 , respectively, and these flange portions  34 , 35  extend opposite each other such that the flange portions  34 , 35  shield the rolling elements  31  in the bearing  22 . It is to be noted that the remaining construction including the oil passage  30  is equivalent to the corresponding construction in the above-described first embodiment. 
         [0042]    In the second embodiment constituted as described above, a portion of the lube oil  26  is also fed to the bearing  22  through the oil passage  30  branching out from the delivery-side lube oil pipe  25 , and the oil passage  30  is also formed in the outer race  33  of the bearing  22 . Therefore, the lube oil  26  is fed to the rolling elements  31  in the bearing  22 , and lubricates the rolling elements  31 . Similar to the first embodiment, it is hence possible to surely feed a sufficient quantity of the lube oil  26  to the rolling elements  31  in the bearing  22  through a shortest distance via the opening of the oil passage  30  and to provide the bearing  22  with improved durability and service life. 
         [0043]    In the second embodiment, it is also possible to restrain the lube oil  26  from flowing out past the rolling elements  31 , reaching the electric motor  6  and contaminating motor oil in the electric motor  6  by the retainer-side flange portion  34  and sleeve-side flange portion  35  extending such that they shield the rolling elements  31 . 
       Third Embodiment 
       [0044]    Referring next to  FIG. 7 , a travel assembly according to a third embodiment of the present invention will be described. 
         [0045]    In this third embodiment, a retainer  21 B and the sleeve  23 A are provided, on a side of the electric motor  6 , with the retainer-side flange portion  34  and the sleeve-side flange portion  35 , respectively, and these flange portions  34 , 35  extend opposite each other such that the flange portions  34 , 35  shield the rolling elements  31  in the bearing  22 . It is to be noted that in the retainer  21 B, an oil passage  30 A is not formed in the outer race  33  of the bearing  22  but is formed in the retainer-side flange portion  34  on a side of the rolling elements  31 . As an opening of the oil passage  30 A, a clearance existing in a side wall of the bearing  22  on a side opposite the electric motor  6  is used. The remaining construction is equivalent to the corresponding construction in the above-described second embodiment. 
         [0046]    In the third embodiment constituted as described above, a portion of the lube oil  26  is also fed to the rolling elements  31  in the bearing  22  through the clearance in the side wall of the bearing  22  by way of the oil passage  30 A branching out from the delivery-side lube oil pipe  25 , and lubricates the rolling elements  31 . Similar to the first embodiment, it is hence possible to surely feed a sufficient quantity of the lube oil  26  to the rolling elements  31  in the bearing  22  through a shortest distance via the opening of the oil passage  30 A and to provide the bearing  22  with improved durability and service life. In the third embodiment, it is also possible to restrain the lube oil  26  from flowing out past the rolling elements  31 , reaching the electric motor  6  and contaminating motor oil in the electric motor  6  owing to the arrangement of the retainer-side flange portion  34  and sleeve-side flange portion  35  extending such that they shield the rolling elements  31 . 
         [0047]    Further, this third embodiment does not require such hole drilling as needed in the first and second embodiments for the arrangement of the oil passage  30  in the outer race  33  of the bearing  22 , and can use, as the bearing  22 , a general-purpose bearing as it is. 
       Fourth Embodiment 
       [0048]    Referring finally to  FIG. 8 , a travel assembly according to a fourth embodiment of the present invention will be described. 
         [0049]    In this fourth embodiment, a retainer  21 C and the sleeve  23 A are provided, on a side of the electric motor  6 , with a retainer-side flange portion  34 A and the sleeve-side flange portion  35 , respectively, and these flange portions  34 A,  35  extend opposite each other such that the flange portions  34 A, 35  shield the rolling elements  31  in the bearing  22 . Of these flange portions  34 A,  35 , the retainer-side flange portion  34 A is formed extending in a radially inward direction such that the respective flange portions  34 A,  35  overlap with each other at end portions thereof. The remaining construction is equivalent to the corresponding construction in the above-described third embodiment. 
         [0050]    In the fourth embodiment constituted as described above, a portion of the lube oil  26  is also fed to the rolling elements  31  through the opening in the outer race  33  by way of the oil passage  30  branching out from the delivery-side lube oil pipe  25 , and lubricates the rolling elements  31 . Similar to the first embodiment, it is hence possible to surely feed a sufficient quantity of the lube oil  26  to the rolling elements  31  in the bearing  22  through a shortest distance via the opening of the oil passage  30  and to provide the bearing  22  with improved durability and service life. 
         [0051]    In the fourth embodiment, it is also possible to surely prevent the lube oil  26  from flowing out past the rolling elements  31 , reaching the electric motor  6  and contaminating motor oil in the electric motor  6  owing to the mutually overlapping arrangement of the retainer-side flange portion  34 A and sleeve-side flange portion  35  extending such that they shield the rolling elements  31 .