Abstract:
An improved final drive is disclosed. The axle includes a double reduction gearbox for off-road machines, which, unlike currently available double reduction gearboxes, contains no planetary gear sets. The improved drive axle contains spur gears having pockets adapted to contain brake disc packs. The pockets may permit utilization of a plurality of brake packs within the gearbox without requiring additional space or enlargement of the gearbox housing. Use of spur gears may thus enable use of fewer gear parts, while use of multiple brake packs may enhance final drive brake capacity, improve longevity of the brake packs, and lengthen brake servicing cycles.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to final drives and, more particularly, relates to integrated brakes incorporated within gearboxes of final drives. 
       BACKGROUND 
       [0002]    Final drives are utilized in a variety of motorized machines, including automobiles, buses and trucks, as well as off-road machines including those involved in construction, mining, and agriculture. The final drives of many off-road machines incorporate gear ratio reductions between their input and output shafts. Such gear reductions have been commonly achieved by either planetary gear sets or a combination of spur and planetary gear sets. One type involving the combination is described in U.S. Pat. No. 5,147,255 granted to Strehler et al., which is incorporated by reference herein. 
         [0003]    Strehler et al. features a double reduction gearbox that incorporates a wet brake system sandwiched between respective spur and planetary gear sets to minimize physical space requirements for brakes of an industrial truck. According to Strehler et al., prior to Strehler et al. brakes were physically contained within structures situated only outside of the drive axle gearbox. As such, Strehler et al. introduces the placement of a wet brake inside of a drive axle gearbox. 
         [0004]    Disadvantages of Strehler et al. include spatial limitations with respect to the amount of braking surface that can be contained within the Strehler gearbox, as well as limitations on potential physical locations of actual brake structures within Strehler&#39;s gearbox. Ideally, a gearbox could be manufactured that contained additional interior space for accommodating increased braking surface, albeit without commensurate requirement of employing a larger gearbox. 
         [0005]    Finally, a major challenge associated with design and construction of gearboxes has been a continuing pressure to achieve more performance and functionality, while using fewer parts in smaller spaces with less weight. Among other things, this has translated into a quest for reducing numbers of gearbox parts, including actual numbers of gears employed, while squeezing additional structures, such as brakes and/or larger brake surfaces, into the gearbox housing envelope. As such, it would be desirable to be able to manufacture a double reduction gearbox possessing substantially fewer gears, while being able to offer greater braking capacity within the housings of gearboxes, albeit without increasing the size of the gearbox housing. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In accordance with one aspect of the disclosure, a final drive gearbox includes an input gear and an output gear, and a reduction gear system interposed between the input and output gears. One gear of the reduction gear system and the output gear are spur gears, each including at least one concave pocket. The pockets may present opportunities to employ greater numbers of wet brake packs over those made available through use of conventional structures. 
         [0007]    In accordance with another aspect of the disclosure, a final drive gearbox includes a plurality of spur gears, each gear defined by a plurality of such annular pockets, and the reduction gear system comprises a double reduction of gear ratios between the input and output gears. 
         [0008]    In accordance with yet another aspect of the disclosure, a final drive gearbox is disclosed in which the reduction gear system comprises first and second reduction gears in mesh respectively with the input and output gears, and in which each of the gear reductions has a reduction ratio of, for example, 5:1. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a side elevation cross-sectional view of a prior art double reduction final drive gearbox containing a set of wet brakes; and 
           [0010]      FIG. 2  is a side elevation cross-sectional view of one preferred embodiment of an improved double reduction final drive gearbox constructed in accordance with the teachings of this disclosure, the improved gearbox containing spur gears having pockets and employing a plurality of wet brakes. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring initially to  FIG. 1 , a prior art final drive gearbox  17 , also known in the art as a transmission, includes a transmission housing  21  adapted to receive and support an input shaft  16 . A spur pinion gear  24  is fixed to the driving end of the input shaft  16 , is in constant mesh therewith, and is adapted to drive a spur gear  25 . The spur gear  25  is rotatably supported and axially movable on a cylindrical roller bearing  27 . A wet brake  20  incorporates an annular first disc carrier  28  fastened to the spur gear  25 , and supports a plurality of first braking discs  31 . The discs  31  are so-called inner discs that are axially splined to the carrier  28  and rotatably movable therewith. 
         [0012]    The inner discs  31  are axially movable on an external tooth system  29  of the first disc carrier  28 . An annular second disc carrier  30  is positioned radially inwardly of the first disc carrier  28 , and is fixed against movement relative to the transmission housing  21 . The second disc carrier  30  supports a plurality of second braking discs  32 , also variously referred to as outer discs. The outer discs  32  are splined to, and are thus axially movable on, an internal tooth system  33  of the second disc carrier  30 . 
         [0013]    As noted, the first disc carrier  28  is fastened to the spur gear  25 ; the spur gear terminates on the driven side thereof at, and is fixed to, a sun gear  34  of a planetary gear set  12 . The sun gear  34  drives a set of planetary gears  36  that mesh with the internal teeth of a ring gear  37 , the ring gear being fixed against rotation relative to the transmission housing  21 . The planetary gears  36  are mounted on, and are rotatable with, a planetary carrier  39 , which in turn is fixed to a wheel shaft  8 . The shaft  8 , rotatably supported by bearings, extends through an opening of the housing  21  and terminates in a wheel flange  18 . The front drive wheel  9  of an associated industrial truck is attached to the wheel flange  18  by bolts shown but not referenced. 
         [0014]    Finally, the brake  20 , defined substantially by inner and outer braking discs  31 ,  32 , is operated by a lever  40  connected to a cable line  43  as shown. Actuation of the cable line via the lever  40  urges a pressure pin  44  leftwardly against the sun gear  34  which, together with the first disc carrier  28  and spur gear  25 , moves axially leftwardly, and in turn compresses the inner and outer braking discs  31 ,  32  together against an annular reaction bearing surface  45 . Since the bearing surface is fixed against rotation relative to the housing  21 , and thus with respect to the second disc carrier  30 , the brake  20  is effective to slow and/or stop the drive wheel  9  of the truck. 
         [0015]    Upon release of the brake  20  by the cable actuated lever  40 , the pin  44  is urged axially rightwardly by a cup spring  46 , effectively releasing the brake discs  31 ,  32 , thereby canceling the braking action and permitting return of the spur gear  25  and the sun gear  34  into their respective initial positions. 
         [0016]    Those skilled in the art will appreciate that the foregoing description represents current state-of-the-art with respect to dual stage or double reduction gearboxes, including all aforenoted limitations with respect to the numbers of gear parts employed, and to the opportunities for placement of wet brakes within interiors of gearbox or transmission housings. 
         [0017]    Referring now to  FIG. 2 , an improved final drive gearbox  100  may include a gearbox housing  106 , and an input shaft  102  supported on an outboard bearing  104  affixed to and supported by a wall  107  of the housing  106 . A corresponding inboard bearing  108 , may also be supported by the wall  107  of the housing  106 , may be adapted to support the inboard end of input shaft  102 . An annular or sleeve styled input gear  110  having input gear teeth  112  may be positioned intermediately of the outboard and inboard bearings  104 ,  108 . 
         [0018]    It should be noted that the disclosed gearbox  100  may contain only pocket styled spur gears. The result may be a significant reduction in the physical number of gears required within the gearbox housing, to the extent that comparable reduction planetary gear sets each include a sun gear, a ring gear, and generally at least three planetary gears. By contrast, the disclosed embodiment of the double reduction spur gearbox may contain only four gears; two for enabling the first reduction, and two for enabling the second reduction. 
         [0019]    The simplicity of the described gearbox  100  as compared to a planetary gearbox may be further appreciated as follows. Each set of gear teeth described herein may be circumferentially arranged about its respective gear, the interaction of each gear being only to mesh with the teeth of a radially adjacent mating gear, as herein described. By contrast, a planetary gear set incorporates a carrier that yokes the multiple planetary gears together to rotate as a slaved unit, the planetary gears generally being driven by the sun gear, which along with the planetary gears are all rotated within a fixed ring gear. The torque loads imposed by a planetary carrier on the various planetary gear teeth may be considerable, and can impose deleterious forces that tend to reduce gear teeth life. Such torque loads may be substantially reduced through the use of the spur gear structures disclosed herein. 
         [0020]    The input gear teeth  112  are in constant mesh with mating teeth  114  of a first reduction gear  116 , which may incorporate a hub  118  that rotates about an idler shaft  120 . A second reduction gear  122 , also displayed herein as a sleeve gear, may extend axially from the hub  118 . The first and second reduction gears  116 ,  122  may be supported by bearings  124  and  126  through which the idler shaft  120  may extend. The first and second reduction gears,  116 ,  122 , along with the shaft  120 , together comprise a reduction gear system  115 . 
         [0021]    Although depicted here as sleeve gears, the input gear  110  and the second reduction gear  122  may alternatively be formed as integral parts of the input and idler shafts  102 ,  120 , respectively; i.e. the gear teeth  112 ,  128  may be formed by gear machining operations performed on exterior surfaces of the respective shafts. 
         [0022]    An output gear  132  contains teeth  130  which mesh with teeth  128  of the second reduction gear  122 . The output gear  132  is secured to a final drive output shaft  134 , variously referred to also as a low speed and/or high torque shaft. Conversely, the input shaft  102  is variously referred to as the high speed and/or low torque shaft. Through the double reduction gear system described, a significant speed reduction may be achieved between the input gear  110  and the output gear  132 . For example, utilizing a pair of 5:1 ratio reductions, the output gear  132  may be made to rotate at one twenty-fifth the speed of the input gear  110 . Commensurately, the torque produced by the output gear  132  would be substantially higher than the torque measured at gear  110 . Although the example provided herein is a 5:1 ratio reduction, other reductions such as 3:1 or 4:1 could be useful in certain settings. 
         [0023]    In the disclosed embodiment, the input and output shafts  102 ,  134  may be aligned along and thus share a common axis “a-a” as shown. This feature, along with the aspect that the idler shaft  120  and the gears  116 ,  122  fixed thereon are situated along an axis “b-b” that is parallel to the axis “a-a”, may provide advantages related to the manufacturing of the gearbox  100 . 
         [0024]    The output shaft  134  may be supported by the inner race of a single bearing  136 . The outer race of the bearing  136  may be secured to an interior wall  107  of the gearbox housing  106 , as shown. Finally, the driving wheels of a machine (neither shown) may be affixed to the shaft  134  for high torque rotation thereof. 
         [0025]    As disclosed, the gearbox  100  may contain a total of four gears designed and arranged in dual reduction stages, each stage adapted to produce an identical reduction, e.g. 5:1, to that available through a set of planetary gears. The gearbox  100  may thus afford a significant savings in the number of gear parts over the combination planetary and spur gear structure of the prior art such as Strehler et al. The latter would typically employ up to seven separate gear structures to achieve the identical amount of speed reduction. 
         [0026]    It may be particularly noted that the first reduction gear  116  and the output gear  132  are of a type described herein as pocket gears. The pocket gears may be machined to have at least one annular pocket  150  on one side of the gear  116 , and at least one pocket  160  on one side of gear  132 . The pockets  150 ,  160  may be physically described as concave rings situated symmetrically about the rotational axis of the gear; the gear sidewalls  152 ,  154  defining bottoms of opposed concave rings. With respect to gear  116 , the sidewalls  152 ,  154  may extend radially from the gear hub  118  to the inside rim or backside  156  of the laterally wider gear tooth ring body  158 . The pocket  150  may be situated on one side, or alternatively the use of dual opposed pockets  150 ,  150 ′, defined in part by sidewalls  152 ,  154 , may be situated on respective sides (left and right, as shown in this described preferred embodiment) of the first reduction gear  116 . 
         [0027]    Correspondingly similar pocket structures  160  may be situated on, and be similarly described with respect to, the output gear  132 . As defined, the pockets  150  and  160  may provide openings for piston actuated hydraulic wet brake packs  180 , shown and described in detail for only the right side pocket  150 ′; i.e., the pocket having its bottom defined by the right gear sidewall  154  of the gear  116 . Two wet brake packs may be utilized in the pockets  150 ,  160  of the presently described embodiment, although up to four such wet brake packs  180 ,  180 ′ may be employed in the available pocket space. Each wet brake pack  180 ,  180 ′ may have a set of rotatable brake discs  182  interleaved with fixed brake discs  184 . The rotatable brake discs  182  may be splined to move along axially extending splines (not shown) in the backside  156  of the gear tooth ring body  158  of the first reduction gear  116 . The discs  184  may be fixed with respect to the housing  106 , and move along splines (not shown) contained on a brake reaction ring  185  (shown only at the brake pack  180 ′) secured to the housing wall  107 . 
         [0028]    The interleaved inner and outer wet brake discs  182 ,  184  are analogous to the aforedescribed inner and outer prior art brake discs  31  and  30 , respectively. In same manner, the discs  182  and  184  may be splined for axial movement, and forced together by a hydraulic piston  186 , the gear sidewall  154  providing a braking reaction plate. Alternatively, a separate reaction plate (not shown) may be installed against the gear sidewall  154  without compromising space requirements. For example, such a reaction plate may be constructed of a thin hardened metal plate, interposed between the sidewall  154  and the wet brake pack  180 . 
         [0029]    It will be noted that a hub  170  may be provided on the output gear  132 , the hub being adapted for rotation of the gear on the bearing  136 , analogously to the hub  118  of the first reduction gear  116 . However, the hub  170  may be designed differently as shown to receive the bearing  136  axially therein. The outer race of the bearing  136  may be secured to the interior of the hub  170  for rotation therewith, and the left end  103  of the shaft  102  may be piloted within the inner race of the bearing  136  to provide additional support. The pockets  150 ,  160  may provide means for accommodation of a plurality of brake packs, only two of which are depicted in the disclosed embodiment of  FIG. 2 . Additional brake packs  180  may be accommodated within the various pockets  160 ,  180  without requiring expansion or increase in size of the housing  106 , as may become appreciated by those skilled in the art. Among other advantages, such use of multiple brake packs may be effective to reduce brake change cycle times, as braking loads may now be carried by multiple brake packs instead of by a single or unitary brake pack. 
       INDUSTRIAL APPLICABILITY 
       [0030]    The technology disclosed herein may have industrial applicability in a variety of settings such as, but not limited to, enhancing braking capacity of final drives. As an improvement over typical planetary gear sets employed in double reduction gearboxes, the use of spur gears may be effective to reduce the required number of gears from ten to four. In addition, the use of spur gears for first reduction and output gears, with each gear having at least one concave pocket, may provide for the economical utilization of a plurality of sets of wet disc brakes within a gearbox without requirement of additional gearbox housing volume to contain the brakes. 
         [0031]    A double reduction gearbox constructed in accordance with the teachings of the above disclosure may thus more economically provide final drive gear reductions with significantly reduced numbers of gear parts. The initial gear reduction may be provided by a simple input gear in mesh with a first reduction gear including at least one wet disc brake pack in at least one pocket thereof. A plurality of such pocket accommodated wet brakes may be employed to substantially reduce overall brake wear rates, enhance longevity of the brakes, and otherwise offer greater braking capacities over gearboxes containing planetary gear sets. 
         [0032]    The input and first reduction gears may be arranged on radially spaced parallel shafts in a very simple construction mode as compared to commonly used planetary gear sets. The second reduction gear may share the same shaft with the first reduction gear, but mesh with the output gear. Moreover, the input gear and the output gears may share the same axis. 
         [0033]    As disclosed, the use of spur gears having such pockets may provide an opportunity for utilization of at least two or more sets of wet disc brakes within a final drive gearbox, to otherwise enhance longevity of the brakes and/or to provide an improved braking capacity over that afforded by comparable double reduction gearboxes containing planetary gear sets. Such an improved gearbox might be advantageously utilized in a work machine, track-type tractor, road grader, truck, pipe layer, roller, forestry machine or other type of industrial machine useful in construction, mining, or agriculture. 
         [0034]    In summary, the disclosed spur gear final drive gearbox may offer a) use of only spur gears to substantially reduce the overall number of gears while providing same reduction as a planetary gearbox, and 2) use of a plurality of brake packs within the gearbox without requiring a larger gearbox. 
         [0035]    A method of manufacturing the improved final drive gearbox disclosed herein may include the following steps: 
         [0000]    a) forming a housing having two pairs of axially opposed openings, each pair of openings defining a first axis and a second axis, each axis parallel and radially spaced apart from the other;
 
b) providing and installing bearings within said housing, each bearing symmetrically positioned along each axis at one of said openings and adapted to support one end of a pair of parallel shafts, each shaft extending along one of said axes and between each pair of openings;
 
c) installing an input gear on an input shaft, and inserting said input gear and input shaft through one of said pair of openings;
 
d) forming an output gear as a spur gear having annular axially opposed pockets on each side thereof; installing said output gear on an output shaft and inserting said output gear and output shaft through the opposed other of said one of said pair of openings in a manner such that said input and said output shafts are axially aligned along said first axis;
 
e) forming a gear reduction system by forming first and second reduction gears, said first reduction gear also formed as a spur gear having annular axially opposed pockets on each side thereof;
 
f) forming an idler shaft adapted to carry and support said first and second reduction gears;
 
g) fixing said first and second reduction gears to said idler shaft;
 
h) inserting said idler shaft along said second axis through said second pair of openings, such that said idler shaft is supported by respective bearings associated with said openings, said input and first reduction gears mesh with one another, and said second reduction and output gears mesh with one another; and
 
i) inserting at least two wet brake packs within said pockets, only one brake pack being contained within each one of said pockets.
 
         [0036]    Lastly, the method steps may also include the step of forming each of said first and second gear reductions to be a 5:1 reduction ratio reduction, for example. In addition, the method steps may also include the steps of a) supporting said output shaft by a single bearing in said housing, and b) piloting the left end of said input shaft within said single bearing.