Abstract:
A multi-mode hybrid drive train offers selective operation in any one of series, parallel, and power split modes. The multi-mode hybrid drive train includes two planetary gear sets and a collection of specifically placed brakes and clutches relative to those gear sets. The first planetary gear train includes a power input for receiving power from a primary rotational power source, as well as a first sun gear, first carrier and first ring gear. The second planetary gear train similarly includes a power input as well as a second sun gear, a second carrier connected to a final drive, and a second ring gear. A first motor is linked to the first sun gear and a second motor is linked to the second sun gear such that selective activation of the clutches, brakes, and motors places the multi-mode hybrid drive train in a selected mode of operation.

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to power transmission systems and, more particularly to a reconfigurable power transmission system that provides multiple modes of operation. 
     BACKGROUND 
     In any power transmission system for providing machine movement, it is important to efficiently transfer power from a power source to a driven implement such as a wheel, track, or other ground-engaging system. With respect to electrical/hybrid drive trains, various transmission formats have arisen to provide this function, each having distinct advantages, as well as potential disadvantages relative to the others. Such formats include for example series, parallel and power split formats. 
     Unfortunately, the formats are generally mutually exclusive, and it has been necessary to forgo the advantages of all but one format in any given implementation. As a result designers have been required to select the format with the most advantages for a particular implementation, with the understanding that the selected format will in some instances be disadvantageous. For example, a format that provides efficient high speed operation may be inefficient or ineffective during a different mode of operation such as start up. 
     Thus, although electrical/hybrid machines have in general been very successful, the available drive trains have been inadequate to fully realize the benefits of these power systems. The disclosed principles provide a mechanism for overcoming the noted deficiencies as will be appreciated from the following description. 
     SUMMARY 
     In an aspect of the disclosed principles, a multi-mode hybrid drivetrain is provided for selective operation in any one of series, parallel, and power split modes. The multi-mode hybrid drive train includes two planetary gear sets and a collection of specifically placed brakes and clutches relative to those gear sets. The first planetary gear train includes a power input for receiving power from a primary rotational power source, as well as a first sun gear, first carrier and first ring gear. The second planetary gear train similarly includes a power input as well as a second sun gear, a second carrier connected to a final drive, and a second ring gear. 
     For configuration, the multi-mode hybrid drive train includes a first clutch for selectively clutching the first carrier to the second carrier and a second clutch for selectively clutching the first sun gear to the second ring gear. It further includes a first brake for selectively braking the first carrier, a second brake for selectively braking the first sun gear, and a third brake for selectively braking the second ring gear. A first motor is linked to the first sun gear and a second motor is linked to the second sun gear such that activation of the clutches, brakes, and motors in a first combination places the multi-mode hybrid drivetrain in a series mode of operation, activation of the clutches, brakes, and motors in a second combination places the multi-mode hybrid drive train in a parallel mode of operation, and activation of the clutches, brakes, and motors in a third combination places the multi-mode hybrid drive train in a power split mode of operation. 
     Further aspects and features of the disclosed principles will be appreciated from the following detailed description and the accompanying drawings, of which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a reconfigurable power transmission according to an embodiment of the described principles; 
         FIG. 2  is a schematic view of the reconfigurable power transmission of  FIG. 1 , showing clutch, brake, and electrical inputs/outputs arranged to provide a series mode configuration; 
         FIG. 3  is a schematic view of the reconfigurable power transmission of  FIG. 1 , showing clutch, brake, and electrical inputs/outputs arranged to provide a parallel mode configuration; 
         FIG. 4  is a schematic view of the reconfigurable power transmission of  FIG. 1 , showing clutch, brake, and electrical inputs/outputs arranged to provide an input CVT configuration; 
         FIG. 5  is a schematic view of the reconfigurable power transmission of  FIG. 1 , showing clutch, brake, and electrical inputs/outputs arranged to provide a compound CVT configuration; and 
         FIG. 6  is a chart illustrating actuation settings correlated to various operational modes in an embodiment of the disclosed principles. 
     
    
    
     DETAILED DESCRIPTION 
     In overview, this disclosure relates to power transmission in electrical/hybrid systems, and the disclosed principles provide a drivetrain that may be reconfigured in real-time through the engagement or disengagement of multiple control units (brakes and clutches), to generate various drive train configurations including series, parallel and CVT. In one embodiment, the system employs two clutches, three brakes and two planetary gear trains to provide reconfigurability as well as to provide multiple operational modes such as neutral, electrical reverse, engine start/stop, extended driving duration, etc. 
     Turning to the figures,  FIG. 1  is a schematic view of a reconfigurable power transmission according to an embodiment of the described principles. As can be seen, the drivetrain  100  of  FIG. 1  takes a power input from an engine  101  or other type of primary power source (hydraulic motor, etc), as well as taking power from or providing power to two motor/generator units including a first motor/generator unit  103  and a second motor/generator unit  105 . The output of the drivetrain  100  is provided at a final drive  107 , e.g., to drive a ground engaging track/wheel/sprockets, etc. 
     The disclosed drive train  100  includes a number of transmission elements and actuators to provide drive and reconfiguration functions. These include a first planetary gear set  109  and a second planetary gear set  111 , as well as a first brake (B 1 )  113 , a second brake (B 2 )  115 , and a third brake (B 3 )  117 . The system  100  further includes a first clutch (C 1 )  119  and a second clutch (C 2 )  121 . The engine  101  provides a power input to the ring gear R 1  of the first planetary gear set  109  while the carrier C 1  of the first planetary gear set  109  is clutched via the first clutch  119  to the carrier C 2  of the second planetary gear set  111  and to the final drive  107 . The carrier C 1  of the first planetary gear set  109  is also linked to the third brake  117 . The sun gear S 1  of the first planetary gear set  109  is linked to the first brake  113  and the first motor/generator  103 , as well as being clutched via the second clutch  121  to the ring gear R 2  of the second planetary gear set  111 . The ring gear R 2  of the second planetary gear set  111  is also linked to the second brake  115 . The sun gear S 2  of the second planetary gear set  111  is linked to the second motor/generator  105 . 
     Selective actuation of the first brake  113 , second brake  115 , third brake  117 , first clutch  119  and second clutch  121  is used to reconfigure the drive train  100  to correspond to a series, parallel or CVT format or configuration.  FIG. 2  illustrates an example of a series mode configuration. In particular, the illustrated drive train  200  is configured such that the engine  201  drives the first motor/generator  203 , which is acting as a generator, through the first planetary gear set  209 . This generates power for use by the second motor/generator  205 , which is acting as a motor. A motor controller  230  may be used to manage the transfer of energy to the second motor/generator  205 . The second motor/generator  205  in turn drives the final drive  207  via the second planetary gear set  211 . 
     In order to provide this configuration, the second brake  215  and the third brake  217  are engaged. In this way, the input to the first motor/generator  203  (i.e., the output of the first planetary gear set  209 ) is directly proportional to the speed of the engine  201  and the output of the second planetary gear set  211  is directly proportional to its input, i.e., to the speed of the second motor/generator  205 . Thus, in this configuration, the generation and use of electrical power occur in series, with no direct mechanical link between the engine  201  and the final drive  207 . 
     As noted above, the disclosed drive train may also be configured to provide parallel operation, i.e., wherein the final drive is driven by one or both of an engine and an electric motor operating in parallel.  FIG. 3  illustrates the reconfigurable power transmission of  FIG. 1 , showing clutch, brake, and electrical inputs/outputs actuated so as to provide a parallel mode configuration. In the illustrated configuration, the first clutch  319 , the first brake  313 , and the second brake  315  are actuated. In particular, the first clutch  319  links the carrier C 1  of the first planetary gear set  309  to the final drive  307  and to the carrier C 2  of the second planetary gear set  311 . The first brake  313  brakes the sun gear S 1  of the first planetary gear set  309  while the second brake  315  brakes the ring gear R 2  of the second planetary gear set  311 . 
     As a result of these actuations, the engine  301  provides power to the final drive  307  at a ratio set by the gear ratios of the first planetary gear set  309  while the second motor/generator  305  is linked to the final drive at a ratio set by the gears of the second planetary gear set  311 . In this way, the second motor/generator  305  may either receive power from the engine  301  for storage in energy storage system  340  or draw energy from the energy storage system  340  and provide power to the final drive  307  in parallel with the engine  301 . 
       FIG. 4  illustrates another configuration of the disclosed system, wherein the system is configured via selective actuation of braking and clutching mechanisms to operate in an input CVT configuration. In this configuration  400 , the second brake  415  and first clutch  419  are actuated, respectively holding the ring gear R 2  of the second planetary gear set  411  stationary and clutching the carrier C 1  of the first planetary gear set  409  to the carrier C 2  of the second planetary gear set  411  and to the final drive  407 . In this configuration, the power, speed, and rotational direction of the final drive  407  are set by the first motor/generator  403  and the second motor/generator  405 . Thus, this configuration provides a continuously variable output based on the control of two parallel inputs (the motor/generators). 
     In a slightly different configuration, the system acts as a compound CVT, wherein the output characteristics are set by both motors, but wherein the effect of one of the motors is magnified by mechanical compounding. This configuration is illustrated in  FIG. 5 . As can be seen this configuration is created by the actuation of the first clutch  519  and the second clutch  521 , while leaving the three brakes unactuated. This configuration is similar to the parallel input CVT configuration shown in  FIG. 4 . 
     However, rather than holding the ring gear R 2  of the second planetary gear set  511  stationary, this gear is instead clutched to the first motor/generator  503  via the second clutch  521 . In this way, the rotation of the first motor/generator  503  is transferred to both the sun gear S 1  of the first planetary gear set  509  and the ring gear R 2  of the second planetary gear set  511 , providing a compounding effect with respect to the rotation of the first motor/generator  503 . 
     Although the foregoing description discusses specific motor and engine types, the disclosed principles are also applicable with respect to other types of rotary machines. For example, the engine  101  may be any one of a number of fuel converter devices (e.g., gasoline engine, diesel engine, turbine engine, jet engine, etc.), or may be an electrical motion device or hydraulic motor. With respect to the first motor/generator  103  and second motor/generator  105 , these were discussed above as being electrical motors/generators, but may be any other type of rotary power providing/generating device including for example hydraulic pump motors, pneumatic pumps (e.g., air compressors)/motors (e.g., air motors), etc. 
     In overview, and referring again to  FIG. 1 , it will now appreciated that selective actuation of the first brake  113 , second brake  115 , third brake  117 , first clutch  119  and second clutch  121  will allow the disclosed transmission to operate in a selected mode optimized for current conditions. The actuation of various controls to provide expected modes of operation within these configurations will be briefly set forth for the convenience of the reader. 
     The chart  600  of  FIG. 6  sets forth the actuation settings usable to achieve various operational modes. In particular, each mode is associated with an actuation mode for each of the first brake  113  (B 1 ), second brake  115  (B 2 ), third brake  117  (B 3 ), first clutch  119  (C 1 ) and second clutch  121  (C 2 ). The chart  600  also sets forth the status of each motor in each mode. The motor modes include “off,” generator (“g”), motor (“m”) and motor-in-reverse (“m(rev)”). 
     The modes described in the chart  600  include parking (engine off), parking (engine on), neutral, engine start (parking), engine start (neutral), forward (low speed), input eVT, forward (high speed), compound eVT, reverse (electrical powered reverse), reverse (series hybrid reverse), eDry 1 (driving on one motor), and eDry 2 (driving on two motors). It will be appreciated that this is an exemplary list of modes, and that other modes may be employed as well within the described principles. 
     While manual activation of the clutches and brakes of the hybrid transmission is possible, the clutches and brakes are controlled by a controller in an embodiment of the described principles. This is especially useful in modes where simultaneous control of the motors and engine is also required. The controller may be a dedicated controller or may be a portion of a machine controller, engine controller, or transmission controller. In any case, the controller is processor-driven and operates by reading computer-readable instructions, including data where appropriate, from a computer-readable medium, and computer-executing the instructions so read. The computer-readable medium is a tangible medium, and may be a volatile or nonvolatile memory, RAM, ROM, flash drive, optical drive, magnetic drive, etc., as appropriate in a given implementation of the disclosed principles. 
     The controller operates by receiving a user or other selection of a mode, and by responsively activating the necessary clutches and/or brakes to implement the selected mode. While in a given mode, the controller also coordinates the motor/generators and the engine as appropriate to carry out user or machine commands. 
     INDUSTRIAL APPLICABILITY 
     The described system and method are applicable to machines and devices wherein it is desirable to transfer power in a controlled manner from a rotational power source to a ground engaging mechanism such as wheels or tracks. Typically, usage environments include construction, industrial machines and associated equipment. The disclosed principles provide a power transmission that is fully reconfigurable to selectively operate as any one of a number of transmission types depending upon the present needs of the system in which the transmission is used. 
     In this context, the disclosed system facilitates reconfiguration via selective actuation of individual brakes and clutches to operate in a series, parallel, input CVT, or compound CVT configuration. Moreover, within these modes, others of the brakes and/or clutches may be actuated, and the motors appropriately controlled, to provide specific types of operation. For example, selective actuation of these components allows a parking operation with the engine on, a parking operation with the engine off, a neutral operation, forward low speed operation, forward high speed operation, and so on. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, and not to entirely exclude such from the scope of the disclosure unless otherwise indicated. 
     Recitations of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.