Abstract:
A drive arrangement for a machine includes a first planetary gear set, a second planetary gear set, a third planetary gear set, a first motor, a second motor, and a third motor. The first, second, and third motors are drivingly connected to the first, second, and third planetary gear sets to simultaneously generate fewer than three separate output rotations.

Description:
TECHNICAL FIELD 
   The present application is directed to a drive arrangement and, more particularly, to a planetary-type drive arrangement. 
   BACKGROUND 
   Work machines such as, for example, track-type tractors and other heavy construction, agriculture, and mining machines, are used to perform many tasks. To effectively perform these tasks, the work machines require a power source that provides significant power to a drive arrangement. The power source may be an engine such as, for example, a turbine engine, diesel engine, gasoline engine, or natural gas engine operated to generate a torque output at a range of speeds. The drive arrangement may include individual motors driven by the power source and associated with individual traction devices of the work machine. These individual motors must be sized to transmit the entire torque output of the power source to the associated traction device, for if one traction device slips due to unfavorable traction conditions, the entire torque output of the engine will be absorbed by the non-slipping traction device. In addition, due to regenerative forces, it may be possible to load a single motor and associated traction device with the entire torque output of the power source and an additional amount of torque that is being regenerated from a traction device located on an opposite side of the work machine. As a result of these occasional high-torque and/or high power loading situations, these motors are typically oversized for a majority of the work machine operation. In addition to the high component cost of the oversized motors and related packaging issues, operation of these oversized motors during low-torque loading conditions is inefficient. 
   One attempt to reduce the cost and inefficiencies associated with oversized drive arrangements is described in U.S. Pat. No. 5,168,946 (the &#39;946 patent) issued to Dorgan on Dec. 8, 1992. The &#39;946 patent describes an electric drive system having first, second, and third electric motors connected via left and right combining gear sets to respective left and right vehicle tracks. To propel the vehicle in low range operations (e.g., low speed, high torque), the first and second motors are energized, while the a brake is applied to the third motor. To propel the vehicle in high range operations (e.g., high speed, low torque), all three motors are energized. Regeneration of power may be available during high range operations. The use of three motors, rather than two, in high range operations results in a reduction of motor sizes. 
   Although the electric drive system of the &#39;946 patent may reduce some of the cost and inefficiency associated with oversized motors, it may be operationally limited and inefficient. In particular, the third motor may only be used during high range operations. The largest amounts of torque are generated during low range operations that involve steering or traction loss. Because only two motors of the &#39;946 patent propel the vehicle during low range operations, the two operational motors must still be oversized to accommodate the associated high torque loads. In addition, regeneration is most effective during steering operations of the vehicle, which most often occur during low range operation. Because regeneration is only available during high range operations of the vehicle described in the &#39;946 patent, the electric drive system may lack efficiency. 
   The planetary drive arrangement of the present disclosure solves one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   One aspect of the present disclosure is directed to a drive arrangement. The drive arrangement includes a first planetary gear set, a second planetary gear set, a third planetary gear set, a first motor, a second motor, and a third motor. The first, second, and third motors are drivingly connected to the first, second, and third planetary gear sets to simultaneously generate fewer than three separate output rotations. 
   Another aspect of the present disclosure is directed to a method of driving a first and a second traction device. The method includes operating first, second, and third motors to generate fewer than three separate output rotations. The first, second, and third motors are connected to first, second, and third planetary gear sets. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic illustration of an exemplary disclosed work machine; 
       FIG. 2  is a schematic illustration of an exemplary disclosed drive system for the work machine of  FIG. 1 ; and 
       FIGS. 3A and 3B  include a table relating gear connections of additional exemplary disclosed drive arrangements for the drive system of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates an exemplary work machine  10 . Work machine  10  may be a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, work machine  10  may be an earth moving machine such as a track-type tractor. Work machine  10  may alternatively embody an on-highway truck, a passenger vehicle, or any other suitable operation-performing work machine. Work machine  10  may include a power source  12 , a traction device  14 , an operator interface device  16 , and a drive system  18  configured to transmit a power output of power source  12  to traction device  14  in response to an input received via operator interface device  16 . 
   Power source  12  may be configured to produce a power output and may include an internal combustion engine. For example, power source  12  may include a diesel engine, a gasoline engine, a gaseous fuel-powered engine, a turbine engine, or any other type of engine apparent to one skilled in the art. It is also contemplated that power source  12  may embody another source of power such as a fuel cell, a battery, or any other source of power known in the art. 
   Traction device  14  may include tracks  20 L and  20 R located on each side of work machine  10  (only  20 L shown in  FIG. 1 ). Alternatively, traction device  14  may include wheels, belts, or other driven traction devices. Traction device  14  may be driven by drive system  18  to rotate in accordance with output rotations of drive system  18 . 
   Operator interface device  16  may be located within an operator cabin of work machine  10 , in close proximity to a seat and may embody any one of numerous devices to control functions of work machine  10 . In one example, operator interface device  16  may embody a joystick controller. It is contemplated that operator interface device  16  may embody additional or different control devices such as, for example, pedals, levers, switches, buttons, wheels, and other control devices known in the art. 
   Operator interface device  16  may be configured to regulate a travel speed, rimpull torque, and/or travel direction of work machine  10 . In particular, a travel speed and/or rimpull torque of tracks  20 L, R may be proportional to an actuation position of operator interface device  16 . For example, operator interface device  16  may be tiltable about a first pivot axis in a first direction to indicate a desired increase in travel speed and/or rimpull torque of work machine  10 . Similarly, operator interface device  16  may be tiltable about the first pivot axis in a second direction opposite the first direction to indicated a desired decrease in the travel speed and/or rimpull torque of work machine  10 . The travel direction may be controlled by tilting operator interface device  16  about a second pivot axis substantially perpendicular to the first pivot axis causing one of tracks  20 L, R to move at a faster or slower speed, or in an opposite direction from the other one of tracks  20 L, R that is located on the opposite side of work machine  10 . 
   As illustrated in  FIG. 2 , drive system  18  may include numerous components that interact to transmit power from power source  12  to tracks  20 L, R. In particular, drive system  18  may embody an electric transmission having a generator  22 , a first motor  24 , a second motor  26 , a third motor  28 , and a planetary gear arrangement  30 . First, second, and third motors  24 - 28  may be selectively operated to propel work machine  10  in a straight forward or reverse direction and to turn or pivot work machine  10 . It is contemplated that drive system  18  may alternatively embody a hydraulic transmission having a hydraulic pump fluidly connected to drive three hydraulic motors. The output of first, second, and third motors  24 - 28  may provide input power to planetary gear arrangement  30  via input shafts  32 ,  34 , and  36 , respectively. Planetary gear arrangement  30  may be connected to and configured to rotatably drive track  20 L via a first output shaft  38 , and track  20 R via a second output shaft  40 , thereby propelling work machine  10 . 
   Generator  22  may be a three-phase permanent magnet alternating field-type generator configured to produce a power output in response to a rotational input from power source  12 . It is also contemplated that generator  22  may be a switched reluctance generator, a direct phase generator, or any other appropriate type of generator known in the art. Generator  22  may include a rotor (not shown) rotatably connected to power source  12  by any means known in the art such as, for example, by a direct crankshaft connection  39 , via a gear train, through a hydraulic circuit, or in any other appropriate manner. Generator  22  may be configured to produce electrical power output as the rotor is rotated within a stator (not shown) by power source  12 . Generator  22  may be electrically connected to a common bus  41  via a generator inverter (not shown), which may be configured to invert the three-phase alternating power to direct phase power. 
   Common bus  41  may include positive and negative power lines (not shown) that electrically connect the generator inverter to motors  24 - 28  by way of one or more motor inverters (not shown). Common bus  41  may also be electrically connected to power storage devices such as batteries (not shown), capacitors (not shown), and other power storage devices known in the art, and to accessory power loads to provide power to and/or to remove power from common bus  41 . 
   Each of motors  24 - 28  may be permanent magnet alternating field-type motors configured to receive power from common bus  41  and to input power to planetary gear arrangement  30 . It is contemplated that motors  24 - 28  may be switched electric motors, direct phase motors, or any other appropriate type of motors known in the art. It is also contemplated that motors  24 - 28  may supply power to common bus  41  during a power regeneration event (e.g., when tracks  20 L or  20 R drive motors  24 - 28 ). 
   A controller  42  may be communicatively connected to operator interface device  16  and motors  24 - 28 . In particular, controller  42  may be in communication with operator interface device  16  by way of a communication line  43 . Controller  42  may be in communication with motors  24 - 28  by way of communication lines  44 ,  46 , and  48 , respectively. It is contemplated that controller  42  may also be in communication with power source  12 , generator  22 , common bus  41 , and/or one or more sensors (not shown) associated with tracks  20 L, R, if desired. 
   Controller  42  may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of drive system  18 . Numerous commercially available microprocessors can be configured to perform the functions of controller  42 . It should be appreciated that controller  42  could readily embody a general work machine or power source microprocessor capable of controlling numerous work machine or power source functions. Controller  42  may include all the components necessary to perform the required system control such as, for example, a memory, a secondary storage device, and a processor, such as a central processing unit. One skilled in the art will appreciate that controller  42  can contain additional or different components. Associated with controller  42  may be various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others. 
   Controller  42  may be configured to control a power output of motors  24 - 28  in response to one or more input. In particular, controller  42  may receive an input via operator interface device  16  indicative of a desired travel speed, rimpull torque, and/or change in travel direction. Controller  42  may be configured to determine a required power output from planetary gear arrangement  30  and an associated power input from motors  24 - 28  that results in the desired travel speed, rimpull torque, and/or change in travel direction. Controller  42  may then command motors  24 - 28  to input the determined power to planetary gear arrangement  30 . 
   Planetary gear arrangement  30  may include three planetary gear assemblies rotatably supported and aligned along a rotational axis  50  and disposed within a stationary housing (not shown). The structure of the gears, input members, output members, coupling members, and the connections therebetween can be achieved using components known in the art. 
   As will be explained in more detail in connection with the embodiments of this disclosure, a planetary gear set may have at least three elements, including a sun gear, a planet carrier having at least one set of planet gears, and a ring gear. The planet gears of the planet carrier may mesh with the sun gear and the ring gear, and with intermediate planet gears of the same planet carrier if intermediate planet gears are included in the planetary gear set. The sun gear, planet carrier, planet gears, and ring gear may all rotate together simultaneously. Alternatively, each of the sun gear, planet carrier, and ring gear may be held stationary. Each planetary gear set may receive one or more input rotations and generate one or more corresponding output rotations. The change in rotational speed between the inputs and the outputs may depend upon the number of teeth in the sun gear and the ring gear. The change in rotational speed may also depend upon the gear(s) that is used to receive the input rotation, the gear(s) that is selected to provide the output rotation, and which gear, if any, is held stationary. 
   Planetary gear arrangement  30  may include a first planetary gear set  52 , a second planetary gear set  54 , and a third planetary gear set  56 . First planetary gear set  52  may include a sun gear  52   s , a planet carrier  52   p , and a ring gear  52   r . Second planetary gear set  54  may include a sun gear  54   s , a planet carrier  54   p , and a ring gear  54   r . Third planetary gear set  56  may include a sun gear  56   s , a planet carrier  56   p , and a ring gear  58   r.    
   The elements of the planetary gear arrangement  30  may be interconnected to form five rotating members. In particular, as illustrated in the embodiment of  FIG. 2  ring gear  56   r  may be connected to planet carrier  54   p  and to planet carrier  52 - to form the first rotating member. Planet carrier  56   p  may form the second rotating member. Sun gear  56   s  and sun gear  54   s  may be connected to form the third rotating member. Ring gear  52   r  may be connected to ring gear  54   r  to form the fourth rotating member. Sun gear  52   s  may form the fifth rotating member. 
   Planetary gear arrangement  30  may receive a power input from each of motors  24 - 28 . In particular, in the embodiment of  FIG. 2 , motor  24  may be connected to the forth rotating member. Motor  26  may be connected to the third rotating member. Motor  28  may be connected to the second rotating member. 
   Planetary gear arrangement  30  may output power to each of tracks  20 L and  20 R. Specifically, track  20 L may be connected to the first rotating member via output shaft  38 . Track  20 R may be connected to the fifth rotating member via output shaft  40 . 
     FIGS. 3A and 3B  include tables illustrating the interconnections described above with respect to the drive arrangement embodiment of  FIG. 2 , and the interconnections of alternative drive arrangement embodiments. For example, the second embodiment listed in the table of  FIG. 3A  includes ring gear  56   r  connected to sun gear  54   s  and sun gear  52   s  to form the first rotating member driven by motor  28 . In this same embodiment, planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  54   r  and to planet carrier  52   p  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member driven by motor  24 . 
   In the third embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  54   r  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to sun gear  54   s  and to planet carrier  52   p  to form the third rotating member driven by motor  24 . Planet carrier  54   p  may be connected to sun gear  52   s  to form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member that drives track  20 R. 
   In the fourth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may be connected to planet carrier  54   p  to form the first rotating member that drives track  20 L. Planet carrier  56   p  may be connected to planet carrier  52   p  to form the second rotating member driven by motor  24 . Sun gear  56   s  may be connected to sun gear  54   s  and to sun gear  52   s  to form the third rotating member driven by motor  26 . Ring gear  54   r  may form the fourth rotating member driven by motor  28 . Ring gear  52   r  may form the fifth rotating member that drives track  20 R. 
   In the fifth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  54   r  and to sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  52   p  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to ring gear  52   r  to form the fifth rotating member driven by motor  24 . 
   In the sixth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  52   r  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to sun gear  54   s  and to sun gear  52   s  to form the third rotating member driven by motor  26 . Ring gear  54   r  may form the fourth rotating member that drives track  20 R. Planet carrier  54   p  may be connected to planet carrier  52   p  to form the fifth rotating member driven by motor  24 . 
   In the seventh embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to planet carrier  54   p  and sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to sun gear  54   s  and to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member driven by motor  24 . 
   In the eighth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  52   r  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  54   r  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may be connected to planet carrier  52   p  to form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to sun gear  52   s  to form the fifth rotating member driven by motor  24 . 
   In the ninth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may be connected to sun gear  52   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  54   r  and to ring gear  52   r  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may form the fourth rotating member driven by motor  24 . Sun gear  54   s  may be connected to planet carrier  52   p  to form the fifth rotating member driven by motor  26 . 
   In the tenth embodiment listed in the table of  FIG. 3A , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  54   r  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  52   r  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may be connected to sun gear  52   s  to form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to planet carrier  52   p  to form the fifth rotating member driven by motor  24 . 
   In the eleventh embodiment listed in the table of  FIG. 3B , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to planet carrier  54   p  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to sun gear  54   s  and to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may be connected to sun gear  52   s  to form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member driven by motor  24 . 
   In the twelfth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may be connected to sun gear  52   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  54   r  and to ring gear  52   r  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may be connected to planet carrier  52   p  to form the fourth rotating member driven by motor  24 . Sun gear  54   s  may form the fifth rotating member driven by motor  26 . 
   In the thirteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may be connected to sun gear  54   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  54   p  and planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member driven by motor  24 . 
   In the fourteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may be connected to sun gear  54   s  and to sun gear  52   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  26 . Planet carrier  54   p  may be connected to ring gear  52   r  to form the fifth rotating member driven by motor  24 . 
   In the fifteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  54   r  and to sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to ring gear  52   r  to form the third rotating member that drives track  20 R. Planet carrier  54   p  may form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to planet carrier  52   p  to form the fifth rotating member driven by motor  24 . 
   In the sixteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to ring gear  54   r  and to sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to sun gear  54   s  and to planet carrier  52   p  to form the third rotating member driven by motor  24 . Planet carrier  54   p  may form the fourth rotating member driven by motor  26 . Ring gear  52   r  may form the fifth rotating member that drives track  20 R. 
   In the seventeenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may be connected to planet carrier  54   p  and to sun gear  52   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to ring gear  52   r  may to form the fifth rotating member driven by motor  24 . 
   In the eighteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may form the first rotating member driven by motor  28 . Planet carrier  56   p  may be connected to planet carrier  54   p  and to sun gear  52   s  to form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  26 . Sun gear  54   s  may be connected to ring gear  52   r  to form the fifth rotating member driven by motor  24 . 
   In the nineteenth embodiment listed in the table of  FIG. 3B , ring gear  56   r  may be connected to sun gear  54   s  and to sun gear  52   s  to form the first rotating member driven by motor  28 . Planet carrier  56   p  may form the second rotating member that drives track  20 L. Sun gear  56   s  may be connected to planet carrier  52   p  to form the third rotating member that drives track  20 R. Ring gear  54   r  may form the fourth rotating member driven by motor  24 . Planet carrier  54   p  may be connected to ring gear  52   r  to form the fifth rotating member driven by motor  26 . 
   INDUSTRIAL APPLICABILITY 
   While the drive system of the present disclosure has potential application in any work machine, the disclosed drive system has particular applicability in track-type tractors and other heavy construction and mining work machines where steering is accomplished by inducing a moment from a difference in forces applied to opposing tracks. These induced moments may require high torque and/or high power input to function properly. The disclosed drive system may provide a low cost, efficient solution to the high torque and power demands of such work machines. 
   To propel tracks  20 L, R of work machine  10 , power generated by generator  22  may be selectively directed to motors  24 - 28 , which are each connected to different input rotational members of planetary drive arrangement  30 . The amount of power directed to each motor may determine the direction and speed of travel of work machine  10 , and the associated efficiency of drive system  18 . 
   Because all three motors  24 - 28  of drive system  18  may be used throughout the full operating range of work machine  10 , the component cost, efficiency, and design flexibility of work machine  10  may be improved. Specifically, because motors  24 - 28  may operate throughout the operating range of work machine  10 , the power absorbed by drive system  18  may always be divided among three motors, thereby reducing the maximum torque and/or power level experienced by any one motor. By lowering the maximum torque and/or power level experienced by any one motor, the required size of motors  24 - 28  may be reduced. Smaller motors are typically less expensive and more efficient. In addition, the smaller size of motors  24 - 28  may free space on work machine  10 , thereby improving design flexibility of surrounding system components. Further, because motors  24 - 28  may be used during both low and high range applications, additional regeneration of power may be possible, further increasing the efficiency of work machine  10 , as compared to drive systems having motors only usable during a high range operation of the work machine. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed drive arrangement without departing from the scope of the disclosure. Other embodiments of the disclosed drive arrangement will be apparent to those skilled in the art from consideration of the specification and practice of the drive arrangement disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.