Abstract:
A final drive assembly for transmitting torque between an input and an output includes a compound gear assembly. The compound gear assembly includes at least three planetary gear trains and is in driving engagement with the input. Each planetary gear train of the at least three planetary gear trains is adapted to coactively and drivingly engage the output, wherein torque generated by the input is distributed to the output by each of the planetary gear trains.

Description:
This application claims the benefit of prior provisional patent application Ser. No. 60/435,962 filed Dec. 20, 2002. 

   TECHNICAL FIELD 
   The present invention relates to final drive assemblies and more particularly to modifying an input speed, through a compound epicyclic gear assembly, to provide a desired output speed. 
   BACKGROUND 
   It is known to employ relatively high-speed AC motors as one of the primary drivers in power train and transmission design for hybrid or electric type power trains. These types of power trains, especially for use with heavy-duty earthmoving machines, for example, still require gear combinations between the power source and the wheel, typically in the form of a final drive assembly primarily for the purpose of speed reduction. These final drive assemblies require the capability of transferring significant torques in addition to transforming high electric motor shaft speed to a substantially slower axle speed. 
   Final drives are commonly employed on large earth working machines, such as mining dump trucks for example and typically have at least a pair of driven wheels which are rotatably mounted upon corresponding axle housings or spindles. Each wheel may employ a final drive reduction gear train, such as a double-reduction planetary arrangement, drivingly connected with a cylindrical final drive adapter that partially, if not fully, surrounds the final drive ring gear. 
   Power to drive such machines is commonly provided by an internal combustion engine which urges rotation of drive axles, provided by the machine, either through a mechanical transmission and differential arrangement or through generation of electrical power to operate electric motors coupled with the drive axles. 
   As machines increase in size to accommodate larger payloads, the need for more robust drive train components arises, which typically means the use of larger components. For example, it is desirable in trucks which use a planetary final drive to utilize as large a ring gear as reasonably possible to reduce stress on the drive train and increase component life. 
   Known final drive gear train sets have utilized a Ravigneaux gear set for speed modification between an input an output, however these types of gear sets are complicated (including clutches and multiple gear sets) and are typically expensive to implement. Moreover, these aforesaid gear types often still require additional speed reduction devices attached therewith to attain desirable speed reduction resulting in expensive, complicated and large units. 
   Another type of final drive assembly is disclosed by U.S. Pat. No. 4,437,530 issued to De Young et al. on Mar. 20, 1984. A pair of coaxially positioned gear sets, provided within a wheel assembly, provide speed reduction between the input and the wheel assembly. Although less complex and likely less expensive than the Ravigneaux gear set, additional speed modification may be necessary to attain desirable rotational speed reduction performance. 
   The present invention is directed to overcoming one or more of the problems described above. 
   SUMMARY OF THE INVENTION 
   The present invention provides, in one embodiment thereof, a final drive assembly for transmitting torque between an input and an output. The final drive includes a compound gear assembly including at least three planetary gear trains and is in driving engagement with the input. Each planetary gear train of the planetary gear trains are adapted to coactively and drivingly engage the output, wherein torque generated by the input is distributed to the output by each of the planetary gear trains. 
   The present invention further provides a machine having an input including at least one output; and at least one final drive assembly structured and arranged to transmit rotation between the input and the output. The final drive assembly includes a compound gear assembly having at least three planetary gear trains and is in driving engagement with the input. Each planetary gear train of the planetary gear trains is adapted to coactively and drivingly engage the output, wherein torque generated by the input is distributed to the output by each of the planetary gear trains. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is schematic and diagrammatic view of a first embodiment of a final drive assembly according to the present invention; 
       FIG. 2  is a chart showing exemplary overall reduction ratio values for various given ratios for the three gear trains of the final drive assembly of  FIG. 1 ; and 
       FIG. 3  is schematic and diagrammatic view of a second embodiment of a final drive assembly according to the present invention. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present invention. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION 
   Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same or corresponding reference numbers will be used throughout the drawings to refer to the same or corresponding parts. 
   Referring to  FIG. 1 , a machine  10  is shown including a first embodiment of a final drive assembly  12  attached thereto. The final drive assembly  12  includes a compound gear assembly  13  engaged with an output or wheel assembly  14 . The wheel assembly  14  may include a compound rim assembly  16  being adapted to mount thereon a pair of ground-engaging tires  18 , as is customary. In an exemplary embodiment, the wheel assembly  14  is adapted to enclose substantially all of the compound gear assembly  13  therein. Although the wheel assembly  14  is depicted as a tire supporting rim structure combination, it is envisioned that the wheel assembly  14  may also be a mid-roller for a continuous track or belt assembly, or any other ground-engaging output assembly known to those having ordinary skill in the art. Furthermore, although in one exemplary embodiment, the final drive assembly  14  is depicted as providing rotational speed reduction between an input and an output for a ground engaging machine, for example, it is also envisioned that the present invention may be used in accordance with rotational speed amplification between an input and an output for use with machines such as windmills, for example. 
   The final drive assembly  12  includes the compound gear assembly  13  having a first planetary gear train  20 , a second planetary gear train  22  and a third planetary gear train  24 . The first planetary gear train  20  may be driveably engaged by an input device  26 . The first planetary gear train  20  is also connected to the second planetary gear train  22  through a connecting member  28 . In turn, the second planetary gear train  22  is connected to the third planetary gear train  24  through a connecting member  30 . The first planetary gear train  20  is in an outboard position, while the third planetary gear train  24  is in an inboard position. The third planetary gear train  24  is connected to ground  32 , such as a rigid housing or frame member, for example. Notably, each of the first, second and third planetary gear trains  20 ,  22  and  24  are respectively connected to the wheel assembly  14 . In an exemplary embodiment the second and third planetary gear trains may be coaxially aligned. 
   The input  26 , which may be an electric motor, hydraulic motor, internal combustion engine, or hybrid source, for example, is connected to a sun gear  34  of the first planetary gear train  20  through a drive member  36 . The first planetary gear train  20  also includes a planet gear set  38  and a ring gear  40 . The planet gear set  38  may include at least three gears each of which being rotatably supported by a carrier  42  through roller bearing assemblies (not shown), as is customary. The planet gear set  38  is supported on the carrier  42  and, in turn, the carrier  42  transmits output torque to the wheel assembly  14  through a connecting member  44 . The connecting member  44  may be, for example, a drive shaft arrangement, a fastened joint, a welded joint, a gear set, an integral joint or any other high torque transmitting relationship between the wheel assembly  14  and the carrier  42  known to those having ordinary skill in the power train arts. The planet gear set  38  of the first planetary gear train  20  is in mesh with the ring gear  40 . It will be understood that a ratio identified as “e 1 ” represents the number of teeth in the ring gear  40  over the number of teeth in the sun gear  34  such as 3:1, for example. 
   The ring gear  40  of the first planetary gear train  20  is connected to a sun gear  46  of the second planetary gear train  22  through the connecting member  28 . The sun gear  46  of the second planetary assembly  22  is in mesh with a planet gear set  48  and the planet gear set  48  is in mesh with a ring gear  50 . The planet gear set  48  may include at least three gears each of which is rotatably supported by a carrier  52  through roller bearing assemblies, as is customary. The planet gear set  48  is supported on the carrier  52  and, in turn, the carrier  52  transmits torque to the third planetary gear train  24  through the connecting member  30 . The planet gear set  48  of the second planet gear train  22  is in mesh with the ring gear  50  and the ring gear  50  is attached to an inner portion  54  of the rim assembly  16 . A ratio, “e 2 ” represents the number of teeth in the ring gear  50  over the number of teeth in the sun gear  46  and may be 3:1, for example. 
   The planet gear set  48  of the second planetary gear train  22  is connected to a sun gear  56  of the third planetary gear train  24  through the connecting member  30 . The sun gear  56  of the third planetary assembly  24  is in mesh with the planet gear set  58  and the planet gear set  58  is in mesh with a ring gear  60 . The planet gear set  58  may include at least three gears each of which being rotatably supported by a carrier  62  through roller bearing assemblies, as is customary. The planet gear set  58  is supported on the carrier  62  and, in turn, the carrier  62  transmits torque to the reaction member  64 . The reaction member  64  is attached to the ground  32 . The planet gear set  58  is in mesh with the ring gear  60  and the ring gear  60  is attached to the inner portion  54  of the rim assembly  16 . A ratio, “e 3 ” represents the number of teeth in the ring gear  60  over the number of teeth in the sun gear  56  and may be 3:1, for example. 
   Since the carrier  62  of the third planetary gear train  24  is grounded through the reaction member  64 , the planet gear set  58  is prevented from orbiting about the sun gear  56 . Consequently, rotation of the sun gear  56  causes direct rotation of the ring gear  60 . In addition to the third planetary gear train  24  providing direct output to the wheel assembly  14  through its ring gear  60 , the second planetary gear train  22  provides direct output to the wheel assembly  14  through its ring gear  50  and the first planetary gear train  20  provides output to the wheel assembly  14  through its carrier member  42  and drive member  44 . By splitting the torque transmitting and speed reduction duties between the planetary gear trains, an overall high reduction ratio is achieved using common sized planetary gear train units. 
   The overall speed reduction of the planetary assembly  12 , may be expressed as:
 
Reduction= e 1[1+ e 2+ e 2 e 3+ e 3]+1
 
   Exemplary values for the ratios e1, e2 and e3 and the corresponding reductions are provided in  FIG. 2 . It will be understood that the present invention contemplates an infinite number of additional values and the fact that exemplary values have been provided in  FIG. 2  does not limit the scope of the invention in any manner. 
     FIG. 3  illustrates a modified embodiment of the machine  10 ′ employing a final drive assembly  12 ′ including a compound gear assembly  13 , wherein certain corresponding elements are denoted by primed reference numerals. Referring to  FIG. 3 , a second embodiment of a final drive assembly  12 ′ is shown and differs from the final drive assembly  12 , shown in  FIG. 1 , in several respects. One such respect includes the first planetary gear train  20 ′ being inwardly positioned relative the wheel assembly  14 . As a result, the second planetary gear train  22  may be identified as the outboard planetary and the first planetary gear train  20 ′ may be identified as the inboard planetary. 
   In an exemplary embodiment, the compound gear assembly  13 ′, includes the first planetary gear train  20 ′, the second planetary gear train  22  and the third planetary gear train  24 . The first planetary gear train  20 ′ is driveably engaged by the input  26 . The first planetary gear train  20 ′ is also connected to the second planetary gear train  22  through the connecting member  28 ′. In turn, the second planetary gear train  22  is connected to the third planetary gear train  24  through a connecting member  30 . The third planetary gear train  24  is connected to ground  32 , such as a rigid housing or frame member, for example. Notably, each of the first, second and third planetary gear trains  20 ,  22  and  24  are respectively connected to the wheel assembly  14 . 
   The input  26  is connected to the sun gear  34 ′ of the first planetary gear train  20 ′ through a drive member  36 ′. The first planetary gear train  20 ′ also includes a planet gear set  38 ′ and a ring gear  40 ′. The planet gear set  38 ′ may include at least three gears each of which is rotatably supported by a carrier  42 ′ through roller bearing assemblies (not shown), as is customary. The planet gear set  38 ′ is supported on the carrier  42 ′ and, in turn, the carrier  42 ′ transmits output torque to the wheel assembly  14  through a connecting member  44 ′. The connecting member  44 ′ may be, for example, a drive shaft, a fastened joint, a welded joint, a gear set, an integral joint or any other high torque transmitting relationship between the wheel assembly  14  and the carrier  42 ′ known to those having ordinary skill in the power train arts. In an exemplary embodiment, the drive member  36 ′ and the connecting member  28 ′ may be concentric shaft members, for example. The final drive assembly  12 ′ may be utilized, for example, when space within the rim assembly  16  is limited. With the second and third planetary gear trains  22  and  24  enclosed within the rim assembly  16 , the first planetary gear train  20 ′ may be positioned apart from the rim assembly  16  and within an axle housing (not shown), for example. 
   INDUSTRIAL APPLICABILITY 
   Referring to  FIG. 1 , in operation the input  26  provides rotation of the sun gear  34  of the first planetary gear train  20  through the drive member  36 . This, in turn, causes rotation of the gears within the planet gear set  38  and orbiting of the carrier  42  about the sun gear  34 . Since the ring gear  40  is in mesh with the planet gears of the planet gear set  38 , it rotates and concomitantly causes rotation of the sun gear  46  of the second planetary gear train  22  through the connecting member  28 . Similarly, the carrier  52  of the second planet gear set  48  drives the sun gear  56  of the third planetary gear train and, at the same time, the torque is transferred to the rim assembly  16  through ring gear  50  being driven by the planet gear set  48 . Finally, the ring gear  56  of the third planetary gear train  24  causes rotation of the gears of the planet gear set  58 , which in turn, causes rotation of the ring gear  60 . Consequently, torque is transferred to the rim assembly  16  by the ring gear  60  since the carrier  62  is being held stationary by the reaction member  64 . 
   Referring to  FIG. 2 , exemplary overall reduction ratios, or as the case may be, amplification ratios, for given first, second and third planetary gear trains  20 ,  22  and  24  are provided. Notably, an overall speed modification between the input and output may be 49:1 for planetary gear train combinations without any of the planetary gear trains exceeding the individual ratio of a value of three. In other words, by combining three common sized planetary gear trains as contemplated, a significant overall speed modification is obtainable within a compact space. 
   Moreover, since planetary gear train size is kept modest, as a result, slow carrier rotational velocities are obtained which means that there will be low “g” forces on the planet gear bearings and certain pinion bearings. Additionally, since the rotational velocities are low, as a result, there exists little if any parasitic losses due to the churning of gears in lubrication oil. Moreover, the ability to lubricate such moving parts is increased when they are rotating at such lower speeds. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed final drive assembly without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only.