Abstract:
A hybrid driveline which may be operated in a hydrostatic drive mode and a direct drive mode and a method of operating a hybrid driveline in a hydrostatic drive mode and a direct drive mode is provided. The hybrid driveline comprises a power source, a first hydrostatic unit drivingly engaged with the power source, a second hydrostatic unit selectively drivingly engaged with a vehicle output and in fluid communication with the first hydrostatic unit, an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit, and a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit. The hybrid driveline provides the benefits of a series hybrid arrangement and a parallel hybrid arrangement, reduces torque interruptions during operation and shifting procedures, and increases an efficiency of a vehicle the driveline is incorporated in.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to power transmission systems. More particularly, this invention relates to a hybrid hydrostatic transmission for a vehicle, in which the hybrid hydrostatic transmission may be operated in a hydrostatic power transmission mode or a direct drive power transmission mode. 
       BACKGROUND OF THE INVENTION 
       [0002]    Vehicles that incorporate hybrid hydrostatic transmissions, such as earth moving machinery, industrial equipment, and others are typically referred to as having a series hybrid arrangement or a parallel hybrid arrangement. In the series hybrid arrangement, at least one accumulator and a control valve are used to collect energy from or deliver stored energy to a conventional hydrostatic transmission, which includes a first hydrostatic unit drivingly engaged with a power source and a second hydrostatic unit drivingly engaged with a transmission output. In the parallel hybrid arrangement, at least one accumulator and a control valve are used to collect energy from or deliver stored energy to a hydrostatic unit, which is drivingly engaged with both a power source and a transmission output. 
         [0003]    Vehicles which include such hybrid hydrostatic transmissions are typically operated in a working cycle mode and a transport cycle mode. In the working cycle mode, the vehicle typically operates at lower speeds and with a variable gear ratio. Torque interruptions within the hybrid hydrostatic transmissions are strongly disfavored in the working cycle mode. The working cycle mode is typically employed in lifting operations and pushing operations. In the transport cycle mode, the vehicle typically operates at higher speeds and with one or more fixed gear ratios. The transport cycle mode is typically employed in hauling operations or while moving the vehicle between areas the working cycle mode is used in. Increased efficiency of the hybrid hydrostatic transmissions is strongly desired in both the working cycle mode and the transport cycle mode. 
         [0004]    Vehicles which include such hybrid hydrostatic transmissions are also subject to torque interruptions during a shifting procedure between the working cycle mode and the transport cycle mode. Such torque interruptions may result in reduced performance of the vehicle and operator dissatisfaction. 
         [0005]    It would be advantageous to develop a hybrid hydrostatic driveline and a method of operation thereof for a vehicle that provides the benefits of a series hybrid arrangement and a parallel hybrid arrangement, reduces torque interruptions during operation and shifting procedures, and increases an efficiency of a vehicle the hybrid hydrostatic driveline is incorporated in. 
       SUMMARY OF THE INVENTION 
       [0006]    Presently provided by the invention, a hybrid hydrostatic driveline and a method for shifting a powersplit transmission between modes of operation that minimizes torque interruption, increases a fuel efficiency of a vehicle, and increases a range of operating speeds of the vehicle the powersplit transmission is incorporated in, has surprisingly been discovered. 
         [0007]    In one embodiment, the present invention is directed to a hybrid driveline for a vehicle which may be operated in a hydrostatic drive mode and a direct drive mode. The hybrid driveline comprises a power source, a first hydrostatic unit drivingly engaged with the power source, a second hydrostatic unit selectively drivingly engaged with a vehicle output and in fluid communication with the first hydrostatic unit, an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit, and a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit. The hybrid driveline is operated in the hydrostatic drive mode by drivingly engaging the second hydrostatic unit with the vehicle output using the clutching device. The hybrid driveline is operated in the direct drive mode by drivingly engaging the power source with the vehicle output using the clutching device. 
         [0008]    In another embodiment, the present invention is directed to a method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode. The method comprises the steps of providing a power source, providing a first hydrostatic unit drivingly engaged with the power source, providing a second hydrostatic unit selectively drivingly engaged with a vehicle output and in fluid communication with the first hydrostatic unit, providing an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit, providing a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit, drivingly engaging the second hydrostatic unit with the vehicle output using the clutching device to place the hybrid driveline in the hydrostatic drive mode, and drivingly engaging the power source with the vehicle output using the clutching device to place the hybrid driveline in the direct drive mode. 
         [0009]    Embodiments are related, inter alia, to the following examples: 
         [0010]    1. A hybrid driveline for a vehicle which may be operated in a hydrostatic drive mode and a direct drive mode, the hybrid driveline comprising: 
         [0011]    a power source; 
         [0012]    a first hydrostatic unit drivingly engaged with the power source; 
         [0013]    a second hydrostatic unit selectively drivingly engaged with a vehicle output, the second hydrostatic unit in fluid communication with the first hydrostatic unit; 
         [0014]    an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit; and 
         [0015]    a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit; 
         [0016]    a first fluid conduit fluidly connecting a first fluid port of the first hydrostatic unit to a first fluid port of the second hydrostatic unit; 
         [0017]    a second fluid conduit fluidly connecting a second fluid port of the first hydrostatic unit to a second fluid port of the second hydrostatic unit; 
         [0018]    a low range gear; and 
         [0019]    a high range gear; 
         [0020]    wherein the hybrid driveline is operated in the hydrostatic drive mode by drivingly engaging the second hydrostatic unit with the vehicle output through the low range gear using the clutching device and by transferring power from the power source to the vehicle output via the first hydrostatic unit, the fluid conduits, the second hydrostatic unit and the clutching device; and 
         [0021]    wherein the hybrid driveline is operated in the direct drive mode by drivingly engaging the power source with the vehicle output through the high range gear using the clutching device. 
         [0022]    2. The hybrid driveline according to example 1, wherein the accumulator assembly comprises a low pressure accumulator, a high pressure accumulator, and at least one control valve. 
         [0023]    3. The hybrid driveline according to example 2, wherein the at least one control valve has at least a first position and a second position, the at least one control valve in the first position facilitating fluid communication between the high pressure accumulator and the first fluid conduit in fluid communication with the first hydrostatic unit and the at least one control valve in the second position facilitating fluid communication between the high pressure accumulator and the second fluid conduit in fluid communication with the first hydrostatic unit and the second hydrostatic unit. 
         [0024]    4. The hybrid driveline according to example 1, wherein the clutching device comprises a shift collar, a first synchronizer, and a second synchronizer. 
         [0025]    5. The hybrid driveline according to example 1, wherein the clutching device comprises a shift collar, a first synchronizer, and a second synchronizer; the first synchronizer facilitating synchronization engagement between the first hydrostatic unit and the vehicle output and the second synchronizer facilitating synchronization between the second hydrostatic unit and the vehicle output. 
         [0026]    6. The hybrid driveline according to example 1, wherein the clutching device comprises a first clutch and a second clutch; the first clutch facilitating variable driving engagement between the first hydrostatic unit and the vehicle output and the second clutch facilitating variable driving engagement between the second hydrostatic unit and the vehicle output. 
         [0027]    7. The hybrid driveline according to example 6, wherein the first clutch and the second clutch are each wet plate style clutches. 
         [0028]    8. The hybrid driveline according to example 1, further comprising a third hydrostatic unit which may be selectively drivingly engaged with a vehicle output, the third hydrostatic unit in fluid communication with the first hydrostatic unit and the accumulator assembly. 
         [0029]    9. The hybrid driveline according to example 8, wherein the clutching device comprises a first clutch, a second clutch, and a third clutch; the first clutch facilitating variable driving engagement between the first hydrostatic unit and the vehicle output, the second clutch facilitating variable driving engagement between the second hydrostatic unit and the vehicle output, and the third clutch facilitating variable driving engagement between the third hydrostatic unit and the vehicle output. 
         [0030]    10 The hybrid driveline according to example 9, wherein the first clutch, the second clutch, and the third clutch are each wet plate style clutches. 
         [0031]    11. A method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode, the method comprising the steps of: 
         [0032]    providing a power source; 
         [0033]    providing a first hydrostatic unit drivingly engaged with the power source; 
         [0034]    providing a second hydrostatic unit selectively drivingly engaged with a vehicle output, the second hydrostatic unit in fluid communication with the first hydrostatic unit; 
         [0035]    providing an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit; 
         [0036]    providing a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit; 
         [0037]    providing a first fluid conduit fluidly connecting a first fluid port of the first hydrostatic unit to a first fluid port of the second hydrostatic unit; 
         [0038]    providing a second fluid conduit fluidly connecting a second fluid port of the first hydrostatic unit to a second fluid port of the second hydrostatic unit; 
         [0039]    providing a low range gear; 
         [0040]    providing a high range gear; 
         [0041]    drivingly engaging the second hydrostatic unit with the vehicle output through the low range gear using the clutching device and transferring power from the power source to the vehicle output via the first hydrostatic unit, the fluid conduits, the second hydrostatic unit and the clutching device to place the hybrid driveline in the hydrostatic drive mode; and 
         [0042]    drivingly engaging the power source with the vehicle output through the high range gear using the clutching device to place the hybrid driveline in the direct drive mode. 
         [0043]    12. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to example 11, wherein the accumulator assembly comprises a low pressure accumulator, a high pressure accumulator, and at least one control valve. 
         [0044]    13. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to example 12, further comprising the step of placing the at least one control valve in one of a first position and a second position, the at least one control valve in the first position facilitating fluid communication between the high pressure accumulator and the first fluid conduit in fluid communication with the first hydrostatic unit and the at least one control valve in the second position facilitating fluid communication between the high pressure accumulator and the second fluid conduit in fluid communication with the first hydrostatic unit and the second hydrostatic unit. 
         [0045]    14. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to example 13, further comprising the step of applying a rotational force to the vehicle output using one of the first hydrostatic unit and the second hydrostatic unit in fluid communication with the high pressure accumulator and/or 
         [0046]    further comprising the step of collecting energy from the vehicle output using one of the first hydrostatic unit and the second hydrostatic unit in fluid communication with the high pressure accumulator and storing the energy in the high pressure accumulator and/or 
         [0047]    further comprising the step of collecting energy from the power source using the first hydrostatic unit in fluid communication with the high pressure accumulator and storing the energy in the high pressure accumulator to facilitate shifting from the hydrostatic drive mode to the direct drive mode and/or 
         [0048]    further comprising the step of applying a rotational force to the second hydrostatic unit using with the high pressure accumulator to facilitate shifting from the direct drive mode to the hydrostatic drive mode. 
         [0049]    Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
           [0051]      FIG. 1  is a schematic illustration of a hybrid driveline for a vehicle according to an embodiment of the invention; 
           [0052]      FIG. 2  is a schematic illustration of a hybrid driveline for a vehicle according to another embodiment of the invention; 
           [0053]      FIG. 3  is a schematic illustration of a hybrid driveline for a vehicle according to another embodiment of the invention; 
           [0054]      FIG. 4A  graphically illustrates a speed of the vehicle the driveline illustrated in  FIG. 1  is incorporated in during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0055]      FIG. 4B  graphically illustrates a rotational speed of a hydrostatic unit of the driveline illustrated in  FIG. 1  during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0056]      FIG. 4C  graphically illustrates a rotational speed of a power source of the driveline illustrated in  FIG. 1  during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0057]      FIG. 4D  graphically illustrates a displacement of a hydrostatic unit of the driveline illustrated in  FIG. 1  during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0058]      FIG. 4E  graphically illustrates a torque of a power source of the driveline illustrated in  FIG. 1  during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0059]      FIG. 4F  graphically illustrates a mode of a clutching device of the driveline illustrated in  FIG. 1  during a shifting procedure from a series mode of operation to a parallel mode of operation; 
           [0060]      FIG. 5A  graphically illustrates a speed of the vehicle the driveline illustrated in  FIG. 1  is incorporated in during a shifting procedure from a parallel mode of operation to a series mode of operation; 
           [0061]      FIG. 5B  graphically illustrates a rotational speed of a hydrostatic unit of the driveline illustrated in  FIG. 1  during a shifting procedure from a parallel mode of operation to a series mode of operation; 
           [0062]      FIG. 5C  graphically illustrates a rotational speed of a power source of the driveline illustrated in  FIG. 1  during a shifting procedure from a parallel mode of operation to a series mode of operation; 
           [0063]      FIG. 5D  graphically illustrates a displacement of a hydrostatic unit of the driveline illustrated in  FIG. 1  during a shifting procedure from a parallel mode of operation to a series mode of operation; 
           [0064]      FIG. 5E  graphically illustrates a torque of a power source of the driveline illustrated in  FIG. 1  during a shifting procedure from a parallel mode of operation to a series mode of operation; and 
           [0065]      FIG. 5F  graphically illustrates a mode of a clutching device of the driveline illustrated in  FIG. 1  during a shifting procedure from a parallel mode of operation to a series mode of operation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0066]    It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
         [0067]      FIG. 1  schematically illustrates a driveline  110  for a vehicle (not shown). The driveline  110  comprises a power source  112 , a first hydrostatic unit  114 , a second hydrostatic unit  116 , an accumulator assembly  118 , and a clutching device  120 . The first hydrostatic unit  114  is drivingly engaged with the power source  112  and the clutching device  120 . The second hydrostatic unit  116  is drivingly engaged with the clutching device  120 . The accumulator assembly  118  is in fluid communication with the first hydrostatic unit  114  and the second hydrostatic unit  116 . The clutching device  120  may be drivingly engaged with one of the power source  112  and the second hydrostatic unit  116  and an output  122 . The driveline  110  is a hybrid driveline which may be operated in a hydrostatic mode and a direct drive mode. 
         [0068]    The power source  112  applies power to an input  124  of the driveline  110 , and thus the clutching device  120 . The power source  112  is, for example, an internal combustion engine; however, it is understood that the power source  112  may include an electric motor or another source of rotational output. It is understood that the power source  112  may be a hybrid power source including both an internal combustion engine and an electric motor. Further, it is understood that the power source  112  may include an output ratio adjusting device as known in the art. Further, it is understood that the power source  112  may include a clutch (not shown) as known in the art, for one of reducing and interrupting a rotational force transferred to the driveline  110 . 
         [0069]    The input  124  comprises at least one rigid member which is drivingly engaged with the power source  112 , the first hydrostatic unit  114 , and a first input gear  126  of the clutching device  120 . The input  124  may be a single elongate rigid member passing through the first hydrostatic unit  114 ; however, it is understood that the input  124  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0070]    The first hydrostatic unit  114  is a hydraulic axial piston pump having a movable swashplate (not shown) which varies a displacement thereof. However, it is understood the first hydrostatic unit  114  may be any other type of variable displacement pump. As mentioned hereinabove, the first hydrostatic unit  114  is drivingly engaged with the power source  112  through the input  124 . A first fluid port  128  of the first hydrostatic unit  114  is in fluid communication with a first fluid conduit  130 . A second fluid port  132  of the first hydrostatic unit  114  is in fluid communication with a second fluid conduit  134 . 
         [0071]    The second hydrostatic unit  116  is a hydraulic axial piston motor having a movable swashplate (not shown) which varies a displacement thereof. However, it is understood the second hydrostatic unit  116  may be any other type of hydrostatic motor. The second hydrostatic unit  116  is drivingly engaged with a second input gear  136  of the clutching device  120  through an input shaft  137 . A first fluid port  138  of the second hydrostatic unit  116  is in fluid communication with the first fluid conduit  130 . A second fluid port  140  of the second hydrostatic unit  116  is in fluid communication with the second fluid conduit  134 . 
         [0072]    The input shaft  137  comprises at least one rigid member which is drivingly engaged with the second hydrostatic unit  116 , and the second input gear  136  of the clutching device  120 . The input shaft  137  may be a single elongate rigid member; however, it is understood that the input shaft  137  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0073]    The first fluid conduit  130  and the second fluid conduit  134  are conduits used in hydraulic power systems as is known in the art. The first fluid conduit  130  and the second fluid conduit  134  may comprise flexible conduits, rigid conduits, or conduits formed within other components of the driveline  110 . The first fluid conduit  130  is in fluid communication with the first hydrostatic unit  114  through the first fluid port  128  thereof, the second hydrostatic unit  116  through the first fluid port  138  thereof, and the accumulator assembly  118 . The second fluid conduit  134  is in fluid communication with the first hydrostatic unit  114  through the second fluid port  132  thereof, the second hydrostatic unit  116  through the second fluid port  140  thereof, and the accumulator assembly  118 . 
         [0074]    The accumulator assembly  118  comprises a control valve  142 , a low pressure accumulator  144 , and a high pressure accumulator  146 . The accumulator assembly  118  is in fluid communication with the first fluid conduit  130  and the second fluid conduit  134  via the control valve  142 . 
         [0075]    The control valve  142  is a three position, four way directional valve as is known in the art; however, it is understood the control valve  142  may be any other fluid control valve or a plurality of fluid control valves. The control valve  142  includes a first circuit port  148 , a second circuit port  150 , a pair of accumulator ports  152 , and a sliding spool  154 . The control valve  142  is in fluid communication with the first fluid conduit  130 , the second fluid conduit  134 , the low pressure accumulator  144 , and the high pressure accumulator  146 . 
         [0076]    The low pressure accumulator  144  is an accumulator as is known in the art. The low pressure accumulator  144  is a hollow vessel in fluid communication with one of the accumulator ports  152  of the control valve  142 . A quantity of gas within the low pressure accumulator  144  is compressed when hydraulic fluid enters the low pressure accumulator  144 . The low pressure accumulator  144  is configured for operation within a particular pressure range. While not shown, the low pressure accumulator  144  may also be fitted with a flush valve (for draining the low pressure accumulator  144  to a fluid reservoir, not shown), a pressure relief valve (for draining the low pressure accumulator  144  to the fluid reservoir), a proportional valve (for cooperating with the control valve  144  for fluidly connecting the low pressure accumulator  144  to the one of the first fluid conduit  130  and the second fluid conduit  134 ), and a pilot valve (for providing fluid pressure to the control valve  142 ). 
         [0077]    The high pressure accumulator  146  is an accumulator as is known in the art. The high pressure accumulator  146  is a hollow vessel in fluid communication with one of the accumulator ports  152  of the control valve  142 . A quantity of gas within the high pressure accumulator  146  is compressed when hydraulic fluid enters the high pressure accumulator  146 . The high pressure accumulator  146  is configured for operation within a particular pressure range. While not shown, the high pressure accumulator  146  may also be fitted with a flush valve (for draining the high pressure accumulator  146  to the fluid reservoir), a pressure relief valve (for draining the high pressure accumulator  146  to the fluid reservoir), a proportional valve (for cooperating with the control valve  142  for fluidly connecting the high pressure accumulator  146  to the one of the first fluid conduit  130  and the second fluid conduit  134 ), and a pilot valve (for providing fluid pressure to the control valve  142 ). 
         [0078]    The clutching device  120  facilitates selective driving engagement in two different manners: between the input  124  and the output  122  and between the input shaft  137  and the output  122 . Further, it is understood that the clutching device  120  may be placed in a neutral position, where neither the input  124  nor the input shaft  137  is drivingly engaged with the output  122 . The clutching device  120  comprises the first input gear  126 , the second input gear  136 , a high range gear  156 , a low range gear  158 , a shift collar  160 , and the output  122 . The first input gear  126 , the second input gear  136 , the high range gear  156 , the low range gear  158 , the shift collar  160 , and the output  122  are disposed in a housing  162  and are rotatably supported by a plurality of bearings (not shown). 
         [0079]    The first input gear  126  is a spur gear drivingly engaged with an end portion of the input  124 ; however, it is understood that the first input gear  126  may be any other type of gear. The first input gear  126  may be separately formed and splined to the input  124  or the first input gear  126  may be unitary with the input  124 . The first input gear  126  is meshed with the high range gear  156 . 
         [0080]    The second input gear  136  is a spur gear drivingly engaged with an end portion of the input shaft  137 ; however, it is understood that the second input gear  136  may be any other type of gear. The second input gear  136  may be separately formed and splined to the input shaft  137  or the second input gear  136  may be unitary with the input shaft  137 . The second input gear  136  is meshed with the low range gear  158 . 
         [0081]    The high range gear  156  is a spur gear disposed about the output  122 ; however, it is understood that the high range gear  156  may be any other type of gear. The high range gear  156  comprises a set of range gear teeth located on the radially outward-most point of the high range gear  156 . The set of range gear teeth are meshed with a set of gear teeth formed on the first input gear  126 . The high range gear  156  also includes a set of clutch teeth located adjacent the shift collar  160 . The set of clutch teeth of the high range gear  156  may be drivingly engaged with the shift collar  160 . 
         [0082]    The low range gear  158  is a spur gear disposed about the output  122 ; however, it is understood that the low range gear  158  may be any other type of gear. The low range gear  158  comprises a set of range gear teeth located on the radially outward-most point of the low range gear  158 . The set of range gear teeth are meshed with a set of gear teeth formed on the second input gear  136 . The low range gear  158  also includes a set of clutch teeth located adjacent the shift collar  160 . The set of clutch teeth of the low range gear  158  may be drivingly engaged with the shift collar  160 . 
         [0083]    The shift collar  160  is concentrically disposed about and drivingly engaged with the output  122 . The shift collar  160  includes a set of inner collar teeth  164  formed on an inner surface thereof, a first synchronizer  166 , and a second synchronizer  168 . The set of inner collar teeth  164  are engaged with a set of output gear teeth  170  of the output  122 . The shift collar  160  can be slidably moved along the axis of the output  122  as directed manually by an operator of the vehicle or automatically by a controller  172  while maintaining engagement of the inner collar teeth  164  and the set of output gear teeth  170 . A shift fork (not shown) disposed in an annular recess formed in the shift collar  160  moves the shift collar  160  along the axis of the output  122  into a first position, a second position, or a neutral position. A shift mechanism (not shown), which is drivingly engaged with shift collar  160  through the shift fork, is actuated to position the shift collar  160  as directed manually by an operator of the vehicle or automatically by the controller  172 . Consequently, the shift mechanism positions the shift collar  160  into the first position, the second position, or the neutral position. In the first position, the shift collar  160  is drivingly engaged with the set of clutch teeth of the high range gear  156  and the set of output gear teeth  170  of the output  122 . In the second position, the shift collar  160  is drivingly engaged with the set of clutch teeth of the low range gear  158  and the set of output gear teeth  170  of the output  122 . In the neutral position, the inner collar teeth  164  of the shift collar  160  are only drivingly engaged with the set of output gear teeth  170  of the output  122 . It is understood the shift collar  160 , the inner collar teeth  164 , the sets of clutch teeth of the range gears  156 ,  158 , and the synchronizers  166 ,  168 , may be substituted with any clutching device that permits selective engagement of a driving and a driven part. 
         [0084]    The first synchronizer  166  forms a portion of the shift collar  160  adjacent the set of clutch teeth of the high range gear  156 . The first synchronizer  166  is a conventional synchromesh clutch including conical engagement surfaces and chamfered engagement teeth; however, it is understood that the first synchronizer  166  may be another type of synchronizer. As the shift collar  160  is moved from the one of the second position and the neutral position into the first position, a portion of the first synchronizer  166  contacts a portion of the high range gear  156 . As the shift collar  160  continues to move towards the clutch teeth of the high range gear  156 , a difference in rotational speed is reduced between the output  122  and the high range gear  156 , and the shift collar  160  becomes drivingly engaged with the set of clutch teeth of the high range gear  156 . 
         [0085]    The second synchronizer ring  168  forms a portion of the shift collar  160  adjacent the set of clutch teeth of the low range gear  158 . The second synchronizer  168  is a conventional synchromesh clutch including conical engagement surfaces and chamfered engagement teeth; however, it is understood that the second synchronizer  168  may be another type of synchronizer. As the shift collar  160  is moved from the one of the first position and the neutral position into the second position, a portion of the second synchronizer  168  contacts a portion of the low range gear  158 . As the shift collar  160  continues to move towards the clutch teeth of the low range gear  158 , a difference in rotational speed is reduced between the output  122  and the low range gear  158 , and the shift collar  160  becomes drivingly engaged with the set of clutch teeth of the low range gear  158 . 
         [0086]    The output  122  comprises at least one rigid member at least partially rotatably disposed in the housing  162  which is drivingly engaged with the shift collar  160  and at least one drivetrain component (not shown). The set of output gear teeth  170  is formed on a radially extending portion of the output  122 . As shown in  FIG. 1 , the output  122  is configured to be in driving engagement with a pair of drivetrain components at opposing ends thereof. The output  122  may be a single elongate rigid member passing through the housing  162 ; however, it is understood that the output  122  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0087]    The controller  172  is in communication with the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the accumulator assembly  118 , and the clutching device  120 . Further, it is understood that the controller  172  may be in communication with at least one sensor (not shown) configured to measure a state of operation of one of the components of the driveline  110 . Preferably, the controller  172  is in electrical communication with the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the accumulator assembly  118 , and the clutching device  120 . Alternately, the controller  172  may be in communication with the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the accumulator assembly  118 , and the clutching device  120  using pneumatics, hydraulics, or a wireless communication medium. 
         [0088]    The controller  172  is configured to accept an input containing information regarding at least one of an operating condition of the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the accumulator assembly  118 , and the clutching device  120 . The controller  172  uses the input to adjust the at least one of the operating condition of the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the position of the control valve  142 , and the position of the shift collar  160 . The controller  172  performs the adjustment to the operating condition of the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the position of the control valve  142 , and the position of the shift collar  160  based on at least one of the operating condition of the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the pressure within each of the accumulators  144 ,  146 , and the rotational speed of the output  122 . The controller  172  references at least one of a series of instructions and conditions, an operator input, at least one data table, and at least one algorithm to determine the adjustment made to the operating condition of the power source  112 , the first hydrostatic unit  114 , the second hydrostatic unit  116 , the position of the control valve  142 , and the position of the shift collar  160 . 
         [0089]      FIG. 2  illustrates a driveline  210  according to another embodiment of the invention. The embodiment of the invention shown in  FIG. 2  includes similar components to the driveline  110  illustrated in  FIG. 1 . Similar features of the embodiment shown in  FIG. 2  are numbered similarly in series, with the exception of the features described below. 
         [0090]      FIG. 2  schematically illustrates a driveline  210  for a vehicle (not shown). The driveline  210  comprises a power source  212 , a first hydrostatic unit  214 , a second hydrostatic unit  216 , an accumulator assembly  218 , and a clutching device  280 . The first hydrostatic unit  214  is drivingly engaged with the power source  212  and the clutching device  280  through an input  282 . The second hydrostatic unit  216  is drivingly engaged with the clutching device  280  through an input shaft  284 . The accumulator assembly  218  is in fluid communication with the first hydrostatic unit  214  and the second hydrostatic unit  216 . The clutching device  280  may be drivingly engaged with one of the power source  212  and the second hydrostatic unit  216  and an output  286 . The driveline  210  is a hybrid driveline which may be operated in a hydrostatic mode and a direct drive mode. 
         [0091]    The input  282  comprises at least one rigid member which is drivingly engaged with the power source  212 , the first hydrostatic unit  214 , and a portion of a first input clutch  288  of the clutching device  280 . The input  282  may be a single elongate rigid member passing through the first hydrostatic unit  214 ; however, it is understood that the input  282  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0092]    The second hydrostatic unit  216  is a hydraulic axial piston motor having a movable swashplate (not shown) which varies a displacement thereof. However, it is understood the second hydrostatic unit  216  may be any other type of variable displacement motor. The second hydrostatic unit  216  is drivingly engaged with a second input gear  289  of the clutching device  280  through the input shaft  284 . A first fluid port  238  of the second hydrostatic unit  216  is in fluid communication with a first fluid conduit  230 . A second fluid port  240  of the second hydrostatic unit  216  is in fluid communication with a second fluid conduit  234 . 
         [0093]    The input shaft  284  comprises at least one rigid member which is drivingly engaged with the second hydrostatic unit  216 , and a second input gear clutch  290  of the clutching device  280 . The input shaft  284  may be a single elongate rigid member; however, it is understood that the input shaft  284  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0094]    The clutching device  280  facilitates selective driving engagement in two different manners: between the input  282  and the output  286  and between the input shaft  284  and the output  286 . Further, it is understood that the clutching device  280  may be placed in a neutral position, where neither the input  282  nor the input shaft  284  is drivingly engaged with the output  286 . The clutching device  280  comprises the first input clutch  288 , the second input clutch  290 , a first input gear  292 , and the second input gear  289 . The first input clutch  288 , the second input clutch  290 , the first input gear  292 , the second input gear  289 , and the output  286  are disposed in a housing  295  and are rotatably supported by a plurality of bearings (not shown). 
         [0095]    The first input clutch  288  is a wet plate style clutch which may be actuated to drivingly engage the input  282  with the first input gear  292 . Alternately, the first input clutch  288  may be any other style of clutch known in the art, such as a dry plate clutch or a cone clutch. The first input clutch  288  comprises at least a first plurality of plates, a second plurality of plates, and a first clutch actuator (not shown). The first plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the input  282 . Accordingly, the first plurality of plates is drivingly engaged with the input  282 . A plurality of tabs formed along an outer peripheral edge of each of the plates corresponds to the clutch support splines formed in a portion of the input  282 . Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the first plurality of plates. The second plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed on the first input gear  292 . Accordingly, the second plurality of plates is drivingly engaged with the first input gear  292 . A plurality of tabs formed along an inner peripheral edge of each of the plates corresponds to the clutch support splines formed on the first input gear  292 . The second plurality of plates is interleaved with the first plurality of plates. Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the second plurality of plates. The first plurality of plates interleaved with the second plurality of plates is known as a first clutch pack. 
         [0096]    The first clutch actuator is a ring style hydraulic actuator. Such actuators are commonly known in the art. The first clutch actuator includes a piston and a chamber disposed adjacent the first clutch pack. The first clutch actuator is in fluid communication with a high pressure fluid source. Alternately, the first clutch actuator may be a mechanical actuator, a pneumatic actuator, or an electrical actuator. 
         [0097]    The first input gear  292  is a spur gear rotatably disposed on the input  282  and drivingly engaged with the output  286 ; however, it is understood that the first input gear  292  may be any other type of gear. As mentioned hereinabove, the first input gear  292  includes the plurality of clutch support splines formed thereon for engaging with the second plurality of plates. The first input gear  292  also comprises a set of gear teeth located on the radially outward-most point of the first input gear  292 . The set of gear teeth are meshed with a set of gear teeth formed on a first gear portion  296  of the output  286 . When the first clutch actuator is engaged, the input  282  is at least variably drivingly engaged with the first input gear  292  through the first clutch pack. 
         [0098]    The second input clutch  290  is a wet plate style clutch which may be actuated to drivingly engage the input shaft  284  with the second input gear  289 . Alternately, the second input clutch  290  may be any other style of clutch known in the art, such as a dry plate clutch or a cone clutch. The second input clutch  290  comprises at least a first plurality of plates, a second plurality of plates, and a second clutch actuator (not shown). The first plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the input shaft  284 . Accordingly, the first plurality of plates is drivingly engaged with the input shaft  284 . A plurality of tabs formed along an outer peripheral edge of each of the plates corresponds to the clutch support splines formed in a portion of the input shaft  284 . Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the first plurality of plates. The second plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed on the second input gear  289 . Accordingly, the second plurality of plates is drivingly engaged with the second input gear  289 . A plurality of tabs formed along an inner peripheral edge of each of the plates corresponds to the clutch support splines formed on the second input gear  289 . The second plurality of plates is interleaved with the first plurality of plates. Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the second plurality of plates. The first plurality of plates interleaved with the second plurality of plates is known as a second clutch pack. 
         [0099]    The second clutch actuator is a ring style hydraulic actuator. Such actuators are commonly known in the art. The second clutch actuator includes a piston and a chamber disposed adjacent the second clutch pack. The second clutch actuator is in fluid communication with a high pressure fluid source. Alternately, the second clutch actuator may be a mechanical actuator, a pneumatic actuator, or an electrical actuator. 
         [0100]    The second input gear  289  is a spur gear rotatably disposed on the input shaft  284  and drivingly engaged with the output  286 ; however, it is understood that the second input gear  289  may be any other type of gear. As mentioned hereinabove, the second input gear  289  includes the plurality of clutch support splines formed thereon for engaging with the second plurality of plates. The second input gear  289  also comprises a set of gear teeth located on the radially outward-most point of the second input gear  289 . The set of gear teeth are meshed with a set of gear teeth formed on a second gear portion  297  of the output  286 . When the second clutch actuator is engaged, the input shaft  284  is at least variably drivingly engaged with the second input gear  289  through the second clutch pack. 
         [0101]    The output  286  comprises at least one rigid member at least partially rotatably disposed in the housing  295  which is drivingly engaged with the first input gear  292 , the second input gear  289 , and at least one drivetrain component (not shown). The first gear portion  296  and the second gear portion  297  are each a radially extending portion of the output  286 . The first gear portion  296  and the second gear portion  297  may be unitarily formed with the output  286  or the first gear portion  296  and the second gear portion  297  may be formed separate from the output  286  and coupled thereto in any conventional manner. As shown in  FIG. 2 , the output  286  is configured to be in driving engagement with a pair of drivetrain components at opposing ends thereof; however, it is understood that the output  286  may be configured for driving engagement with any number of drivetrain components. The output  286  may be a single elongate rigid member passing through the housing  295 ; however, it is understood that the output  286  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0102]    A controller  298  is in communication with the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the accumulator assembly  218 , and the clutching device  280 . Further, it is understood that the controller  298  may be in communication with at least one sensor (not shown) configured to measure a state of operation of one of the components of the driveline  210 . Preferably, the controller  298  is in electrical communication with the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the accumulator assembly  218 , and the clutching device  280 . Alternately, the controller  298  may be in communication with the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the accumulator assembly  218 , and the clutching device  280  using pneumatics, hydraulics, or a wireless communication medium. 
         [0103]    The controller  298  is configured to accept an input containing information regarding at least one of an operating condition of the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the accumulator assembly  218 , and the clutching device  280 . The controller  298  uses the input to adjust the at least one of the operating condition of the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the position of a control valve  242 , an engagement level of the first input clutch  288 , and an engagement level of the second input clutch  290 . The controller  298  performs the adjustment to the operating condition of the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the position of the control valve  242 , the engagement level of the first input clutch  288 , and the engagement level of the second input clutch  290  based on at least one of the operating condition of the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the pressure within each of the accumulators  244 , and the rotational speed of the output  286 . The controller  298  references at least one of a series of instructions and conditions, an operator input, at least one data table, and at least one algorithm to determine the adjustment made to the operating condition of the power source  212 , the first hydrostatic unit  214 , the second hydrostatic unit  216 , the position of the control valve  242 , the engagement level of the first input clutch  288 , and the engagement level of the second input clutch  290 . 
         [0104]      FIG. 3  illustrates a driveline  310  according to another embodiment of the invention. The embodiment of the invention shown in  FIG. 3  includes similar components to the driveline  110  illustrated in  FIG. 1 . Similar features of the embodiment shown in  FIG. 3  are numbered similarly in series, with the exception of the features described below. 
         [0105]      FIG. 3  schematically illustrates a driveline  310  for a vehicle (not shown). The driveline  310  comprises a power source  312 , a first hydrostatic unit  314 , a second hydrostatic unit  316 , a third hydrostatic unit  317 , an accumulator assembly  318 , and a clutching device  380 . The first hydrostatic unit  314  is drivingly engaged with the power source  312  and the clutching device  380  through an input  381 . The second hydrostatic unit  316  is drivingly engaged with the clutching device  380  through an input shaft  382 . The third hydrostatic unit  317  is drivingly engaged with the clutching device  380  through a second input shaft  383 . The accumulator assembly  318  is in fluid communication with the first hydrostatic unit  314 , the second hydrostatic unit  316 , and the third hydrostatic unit  317 . The clutching device  380  may be drivingly engaged with one of the power source  312 , the second hydrostatic unit  316 , and the third hydrostatic unit  317  and an output  384  of the clutching device  380 . The driveline  310  is a hybrid driveline which may be operated in a hydrostatic mode and a direct drive mode. 
         [0106]    The input  381  comprises at least one rigid member which is drivingly engaged with the power source  312 , the first hydrostatic unit  314 , and a portion of a first input clutch  385  of the clutching device  380 . The input  381  may be a single elongate rigid member passing through the first hydrostatic unit  314 ; however, it is understood that the input  381  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0107]    The second hydrostatic unit  316  is a hydraulic axial piston motor having a movable swashplate (not shown) which varies a displacement thereof. However, it is understood the second hydrostatic unit  316  may be any other type of variable displacement motor. The second hydrostatic unit  316  is drivingly engaged with a second input clutch  386  of the clutching device  380  through the input shaft  382 . A first fluid port  338  of the second hydrostatic unit  316  is in fluid communication with a first fluid conduit  387 . A second fluid port  340  of the second hydrostatic unit  316  is in fluid communication with a second fluid conduit  388 . 
         [0108]    The input shaft  382  comprises at least one rigid member which is drivingly engaged with the second hydrostatic unit  316 , and the second input clutch  386  of the clutching device  380 . The input shaft  382  may be a single elongate rigid member; however, it is understood that the input shaft  382  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0109]    The third hydrostatic unit  317  is a hydraulic axial piston motor having a movable swashplate (not shown) which varies a displacement thereof. However, it is understood the third hydrostatic unit  317  may be any other type of variable displacement motor. The third hydrostatic unit  317  is drivingly engaged with a clutch input gear  389  of the clutching device  380  through the second input shaft  383 . A first fluid port  390  of the third hydrostatic unit  317  is in fluid communication with the first fluid conduit  387 . A second fluid port  391  of the third hydrostatic unit  317  is in fluid communication with the second fluid conduit  388 . 
         [0110]    The second input shaft  383  comprises at least one rigid member which is drivingly engaged with the third hydrostatic unit  317 , and the clutch input gear  389  of the clutching device  380 . The second input shaft  383  may be a single elongate rigid member; however, it is understood that the second input shaft  383  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0111]    The first fluid conduit  387  and the second fluid conduit  388  are conduits used in hydraulic power systems as is known in the art. The first fluid conduit  387  and the second fluid conduit  388  may comprise flexible conduits, rigid conduits, or conduits formed within other components of the driveline  310 . The first fluid conduit  387  is in fluid communication with the first hydrostatic unit  314  through a first fluid port  328  thereof, the second hydrostatic unit  316  through the first fluid port  338  thereof, the third hydrostatic unit  317  through the first fluid port  390  thereof, and the accumulator assembly  318 . The second fluid conduit  388  is in fluid communication with the first hydrostatic unit  314  through the second fluid port  332  thereof, the second hydrostatic unit  316  through the second fluid port  340  thereof, the third hydrostatic unit  317  through the second fluid port  391  thereof, and the accumulator assembly  318 . 
         [0112]    The clutching device  380  facilitates selective driving engagement in three different manners: between the input  381  and the output  384 , between the input shaft  382  and the output  384 , and between the second input shaft  383  and the output  384 . Further, it is understood that the clutching device  380  may be placed in a neutral position, where each of the input  381 , the input shaft  382 , and the second input shaft  383  are not drivingly engaged with the output  384 . The clutching device  380  comprises the first input clutch  385 , the second input clutch  386 , the clutch input gear  389 , a clutch and jackshaft assembly  392 , and the output  384 . The first input clutch  385 , the second input clutch  386 , the clutch input gear  389 , the clutch and jackshaft assembly  392 , and the output  384  are disposed in a housing  393  and are rotatably supported by a plurality of bearings (not shown). 
         [0113]    The first input clutch  385  is a wet plate style clutch which may be actuated to drivingly engage the input  381  with a first input gear  385   a . Alternately, the first input clutch  385  may be any other style of clutch known in the art, such as a dry plate clutch or a cone clutch. The first input clutch  385  comprises at least a first plurality of plates, a second plurality of plates, and a first clutch actuator (not shown). The first plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the input  381 . Accordingly, the first plurality of plates is drivingly engaged with the input  381 . A plurality of tabs formed along an outer peripheral edge of each of the plates corresponds to the clutch support splines formed in a portion of the input  381 . Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the first plurality of plates. The second plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed on the first input gear  385   a . Accordingly, the second plurality of plates is drivingly engaged with the first input gear  385   a . A plurality of tabs formed along an inner peripheral edge of each of the plates corresponds to the clutch support splines formed on the first input gear  385   a . The second plurality of plates is interleaved with the first plurality of plates. Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the second plurality of plates. The first plurality of plates interleaved with the second plurality of plates is known as a first clutch pack  385   b.    
         [0114]    The first clutch actuator is a ring style hydraulic actuator. Such actuators are commonly known in the art. The first clutch actuator includes a piston and a chamber disposed adjacent the first clutch pack  385   b . The first clutch actuator is in fluid communication with a high pressure fluid source. Alternately, the first clutch actuator may be a mechanical actuator, a pneumatic actuator, or an electrical actuator. 
         [0115]    The first input gear  385   a  is a spur gear rotatably disposed on the input  381  and drivingly engaged with first gear portion  394  of the output  384 ; however, it is understood that the first input gear  385   a  may be any other type of gear. As mentioned hereinabove, the first input gear  385   a  includes the plurality of clutch support splines formed thereon for engaging with the second plurality of plates. The first input gear  385   a  also comprises a set of gear teeth located on the radially outward-most point of the first input gear  385   a . The set of gear teeth are meshed with a set of gear teeth formed on the first gear portion  394  of the output  384 . When the first clutch actuator is engaged, the input  381  is at least variably drivingly engaged with the first input gear  385   a  through the first clutch pack  385   b.    
         [0116]    The second input clutch  386  is a wet plate style clutch which may be actuated to drivingly engage the input shaft  382  with a second input gear  386   a . Alternately, the second input clutch  386  may be any other style of clutch known in the art, such as a dry plate clutch or a cone clutch. The second input clutch  386  comprises at least a first plurality of plates, a second plurality of plates, and a second clutch actuator (not shown). The first plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the input shaft  382 . Accordingly, the first plurality of plates is drivingly engaged with the input shaft  382 . A plurality of tabs formed along an outer peripheral edge of each of the plates corresponds to the clutch support splines formed in a portion of the input shaft  382 . Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the first plurality of plates. The second plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed on the second input gear  386   a . Accordingly, the second plurality of plates is drivingly engaged with the second input gear  386   a . A plurality of tabs formed along an inner peripheral edge of each of the plates corresponds to the clutch support splines formed on the second input gear  386   a . The second plurality of plates is interleaved with the first plurality of plates. Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the second plurality of plates. The first plurality of plates interleaved with the second plurality of plates is known as a second clutch pack  386   b.    
         [0117]    The second clutch actuator is a ring style hydraulic actuator. Such actuators are commonly known in the art. The second clutch actuator includes a piston and a chamber disposed adjacent the second clutch pack  386   b . The second clutch actuator is in fluid communication with a high pressure fluid source. Alternately, the second clutch actuator may be a mechanical actuator, a pneumatic actuator, or an electrical actuator. 
         [0118]    The second input gear  386   a  is a spur gear rotatably disposed on the input shaft  382  and drivingly engaged with a second gear portion  395  of the output  384 ; however, it is understood that the second input gear  386   a  may be any other type of gear. As mentioned hereinabove, the second input gear  386   a  includes the plurality of clutch support splines formed thereon for engaging with the second plurality of plates. The second input gear  386   a  also comprises a set of gear teeth located on the radially outward-most point of the second input gear  386   a . The set of gear teeth are meshed with a set of gear teeth formed on the second gear portion  395  of the output  384 . When the second clutch actuator is engaged, the input shaft  382  is at least variably drivingly engaged with the second input gear  386   a  through the second clutch pack  386   b.    
         [0119]    The clutch input gear  389  is a spur gear drivingly engaged with an end portion of the second input shaft  383 ; however, it is understood that the clutch input gear  389  may be any other type of gear. The clutch input gear  389  may be separately formed and splined to the second input shaft  383  or the clutch input gear  389  may be unitary with the second input shaft  383 . The clutch input gear  389  is meshed with a portion of the clutch and jackshaft assembly  392 . 
         [0120]    The clutch and jackshaft assembly  392  may be actuated to drivingly engage the second input shaft  383  with a third input gear  392   a . The clutch and jackshaft assembly  392  comprises a wet plate clutch; however, it is understood that the clutch and jackshaft assembly  392  may be any other style of clutch known in the art, such as a dry plate clutch or a cone clutch. The clutch and jackshaft assembly  392  comprises the third input gear  392   a , a geared input shaft  392   b , a first plurality of plates, a second plurality of plates, and a third clutch actuator (not shown). The first plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the third input gear  392   a . Accordingly, the first plurality of plates is drivingly engaged with third input gear  392   a . A plurality of tabs formed along an inner peripheral edge of each of the plates corresponds to the clutch support splines formed in a portion of the third input gear  392   a . Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the first plurality of plates. The second plurality of plates is drivingly engaged with a plurality of clutch support splines (not shown) formed in the geared input shaft  392   b . Accordingly, the second plurality of plates is drivingly engaged with the geared input shaft  392   b . A plurality of tabs formed along an outer peripheral edge of each of the plates corresponds to the clutch support splines formed on the geared input shaft  392   b . The second plurality of plates is interleaved with the first plurality of plates. Each of the plates is a clutch plate as is known in the art. It is understood that any number of plates may form the second plurality of plates. The first plurality of plates interleaved with the second plurality of plates is known as a third clutch pack  392   c.    
         [0121]    The third clutch actuator is a ring style hydraulic actuator. Such actuators are commonly known in the art. The third clutch actuator includes a piston and a chamber disposed adjacent the third clutch pack  392   c . The third clutch actuator is in fluid communication with a high pressure fluid source. Alternately, the third clutch actuator may be a mechanical actuator, a pneumatic actuator, or an electrical actuator. 
         [0122]    The third input gear  392   a  is a geared member which is rotatably disposed onto the geared input shaft  392   b . The third input gear  392   a  is drivingly engaged with the second gear portion  395  of the output  384 . As mentioned hereinabove, the third input gear  392   a  includes the plurality of clutch support splines formed thereon for engaging with the first plurality of plates. The third input gear  392   a  also comprises a set of gear teeth located on a radially outward-most point of the third input gear  392   a . The set of gear teeth are meshed with a set of gear teeth formed on the second gear portion  395  of the output  384 . When the third clutch actuator is engaged, the geared input shaft  392   b  is at least variably drivingly engaged with the third input gear  392   a  through the third clutch pack  392   c.    
         [0123]    The geared input shaft  392   b  is a geared member onto which the third input gear  392   a  is rotatably disposed. The geared input shaft  392   b  is drivingly engaged with the clutch input gear  389 . As mentioned hereinabove, the geared input shaft  392   b  includes the plurality of clutch support splines formed thereon for engaging with the second plurality of plates. The geared input shaft  392   b  also comprises a set of gear teeth located on a radially outward-most point of the geared input shaft  392   b . The set of gear teeth are meshed with a set of gear teeth formed on the clutch input gear  389 . When the third clutch actuator is engaged, the geared input shaft  392   b  is at least variably drivingly engaged with third input gear  392   a  through the third clutch pack  386   b.    
         [0124]    The output  384  comprises at least one rigid member at least partially rotatably disposed in the housing  393  which is drivingly engaged with at least one drivetrain component (not shown). A set of output gear teeth is formed on both the first gear portion  394  and the second gear portion  395 . The first gear portion  394  and the second gear portion  395  each radially extend from the output  384 . As shown in  FIG. 3 , the output  384  is configured to be in driving engagement with a pair of drivetrain components at opposing ends thereof. The output  384  may be a single elongate rigid member passing through the housing  393 ; however, it is understood that the output  384  may comprise a plurality of rigid members drivingly engaged with one another. 
         [0125]    A controller  396  is in communication with the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the accumulator assembly  318 , and the clutching device  380 . Further, it is understood that the controller  396  may be in communication with at least one sensor (not shown) configured to measure a state of operation of one of the components of the driveline  310 . Preferably, the controller  396  is in electrical communication with the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the accumulator assembly  318 , and the clutching device  380 . Alternately, the controller  396  may be in communication with the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the accumulator assembly  318 , and the clutching device  380  using pneumatics, hydraulics, or a wireless communication medium. 
         [0126]    The controller  396  is configured to accept an input containing information regarding at least one of an operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the accumulator assembly  318 , and the clutching device  380 . The controller  396  uses the input to adjust the at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the position of a control valve  342 , and a state of engagement of each of the first input clutch  385 , the second input clutch  386 , and the clutch and jackshaft assembly  392 . The controller  396  performs the adjustment to the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the position of a control valve  342 , and a state of engagement of each of the first input clutch  385 , the second input clutch  386 , and the clutch and jackshaft assembly  392  based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the pressure within a pair accumulators  344 ,  346  of the accumulator assembly  318 , and the rotational speed of the output  384 . The controller  396  references at least one of a series of instructions and conditions, an operator input, at least one data table, and at least one algorithm to determine the adjustment made to the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the position of a control valve  342 , and a state of engagement of each of the first input clutch  385 , the second input clutch  386 , and the clutch and jackshaft assembly  392 . 
         [0127]    In use, the driveline  110 ,  210  may be operated in at least four different hybrid modes of operation. The hybrid modes of operation of the driveline  110 ,  210  may be described as either series operation (hydrostatic) or parallel operation (direct drive). The series operation of the driveline  110 ,  210  is characterized by a transfer of power from the power source  112 ,  212  to the output  122 ,  286  via the first hydrostatic unit  114 ,  214 , the fluid conduits  130 ,  134 ,  230 ,  234 , the second hydrostatic unit  116 ,  216 , and the clutching device  120 ,  280 . The parallel operation of the driveline  110 ,  210  is characterized by a transfer of power from the power source  112 ,  212  to the output  122 ,  286  via the input  124 ,  282  and the clutching device  120 ,  280 . In either the series operation or the parallel operation of the driveline  110 ,  210 , the accumulator assembly  118 ,  218  may be operated in a manner to apply a rotational force to the output  122 ,  286  or collect energy from the output  122 ,  286  via the first hydrostatic unit  114 ,  214  or the second hydrostatic unit  116 ,  216 ; which define the at least four different hybrid modes of operation of the driveline  110 ,  210 . 
         [0128]    When the driveline  110 ,  210  is placed in the series mode of operation, the set of clutch teeth of the low range gear  158  are drivingly engaged with the shift collar  160  or the second input clutch  290  is actuated while the first input clutch  288  is disengaged. Accordingly, the output  122 ,  286  is driven through the low range gear  158  or the second gear portion  297 . As non-limiting examples, the low range gear  158  or the second gear portion  297  may be configured to provide the driveline  110 ,  210  with a relatively low drive ratio, which may facilitate operation of the driveline  110 ,  210  during repetitive tasks (such as starting and stopping) or operation of the driveline  110 ,  210  in confined areas. 
         [0129]    When the driveline  110 ,  210  is placed in the series mode of operation, the accumulator assembly  118 ,  218  may be operated in a manner to apply a rotational force to the output  122 ,  286  using the second hydrostatic unit  116 ,  216 . To apply a rotational force to the output  122 ,  286 , the controller  172 ,  298  places the sliding spool  154 ,  254  of the control valve  142 ,  242  in a position that allows fluid communication between the high pressure accumulator  146 ,  246  and the first fluid conduit  130 ,  230 . Based on at least one of the operating condition of the power source  112 ,  212 , the first hydrostatic unit  114 ,  214 , the second hydrostatic unit  116 ,  216 , the pressure within each of the accumulators  144 ,  146 ,  244 ,  246 , and the rotational speed of the output  122 ,  286 , the controller  172 ,  298  adjusts a position of the swashplate of each of the first hydrostatic unit  114 ,  214  and the second hydrostatic unit  116 ,  216  to apply a rotational force to the output  122 ,  286  using pressure from the high pressure accumulator  146 ,  246 . Energy stored in the high pressure accumulator  146 ,  246  is applied to the output  122 ,  286  through the second hydrostatic unit  116 ,  216  via the first fluid conduit  130 ,  230 . As a result, fluid passes from the first fluid conduit  130 ,  230  into the second fluid conduit  134 ,  234  and into the low pressure accumulator  144 ,  244  (in fluid communication with the second fluid conduit  134 ,  234  via the control valve  142 ). Applying a rotational force to the output  122 ,  286  using the second hydrostatic unit  116 ,  216  using pressure from the high pressure accumulator  146 ,  246  may be performed, for example, when the driveline  110 ,  210  is accelerating. 
         [0130]    When the driveline  110 ,  210  is placed in the series mode of operation, the accumulator assembly  118 ,  218  may be operated in a manner to collect energy from the output  122 ,  286  using the second hydrostatic unit  116 ,  216 . Energy collected from the output  122 ,  286  using the second hydrostatic unit  116 ,  216  is stored in the high pressure accumulator  146 ,  246 . To collect energy from the output  122 ,  286 , the controller  172 ,  298  places the sliding spool  154 ,  254  of the control valve  142 ,  242  in a position that allows fluid communication between the high pressure accumulator  146 ,  246  and the second fluid conduit  134 ,  234 . Based on at least one of the operating condition of the power source  112 ,  212 , the first hydrostatic unit  114 ,  214 , the second hydrostatic unit  116 ,  216 , the pressure within each of the accumulators  144 ,  146 ,  244 ,  246 , and the rotational speed of the output  122 ,  286 , the controller  172 ,  298  adjusts a position of the swashplate of each of the first hydrostatic unit  114 ,  214  and the second hydrostatic unit  116 ,  216  to collect energy from the output  122 ,  286  by increasing an amount of fluid stored in the high pressure accumulator  146 ,  246 . Energy from the output  122 ,  286  is used to transfer and increase a pressure of fluid from the first fluid conduit  130 ,  230  (in fluid communication with the low pressure accumulator  144 ,  244 ) to the second fluid conduit  134 ,  234  (in fluid communication with the high pressure accumulator  146 ,  246 ). Collecting energy from the output  122 ,  286  by increasing an amount of fluid stored in the high pressure accumulator  146 ,  246  may be performed, for example, when the driveline  110 ,  210  is decelerating or when a braking of the driveline  110 ,  210  is desired. 
         [0131]    When the driveline  110 ,  210  is placed in the parallel mode of operation, the set of clutch teeth of the high range gear  156  are drivingly engaged with the shift collar  160  or the first input clutch  288  is actuated while the second input clutch  290  is disengaged. Accordingly, the output  122 ,  286  is driven through the high range gear  156  or the first gear portion  296 . As a non-limiting example, the high range gear  156  or the first gear portion  296  may be configured to provide the driveline  110 ,  210  with a relatively high drive ratio, which may facilitate operation of the driveline  110 ,  210  during tasks in which the driveline  110 ,  210  is operated at high speeds, such as when the vehicle the driveline  110 ,  210  is incorporated in is undergoing acceleration to high speeds or when the vehicle the driveline  110 ,  210  is incorporated in is moved long distances. 
         [0132]    When the driveline  110 ,  210  is placed in the parallel mode of operation, the accumulator assembly  118 ,  218  may be operated in a manner to apply a rotational force to the output  122 ,  286  using the first hydrostatic unit  114 ,  214 . To apply a rotational force to the output  122 ,  286 , the controller  172 ,  298  places the sliding spool  154 ,  254  of the control valve  142 ,  242  in a position that allows fluid communication between the high pressure accumulator  146 ,  246  and the first fluid conduit  130 ,  230 . Based on at least one of the operating condition of the power source  112 ,  212 , the first hydrostatic unit  114 ,  214 , the pressure within each of the accumulators  144 ,  146 ,  244 ,  246 , and the rotational speed of the output  122 ,  286 , the controller  172 ,  298  adjusts a position of the swashplate of the first hydrostatic unit  114 ,  214  to apply a rotational force to the output  122 ,  286  using pressure from the high pressure accumulator  146 ,  246 . Energy stored in the high pressure accumulator  146 ,  246  is applied to the output  122 ,  286  through the first hydrostatic unit  114 ,  214  via the first fluid conduit  130 ,  230 . As a result, fluid passes from the first fluid conduit  130 ,  230  into the second fluid conduit  134 ,  234  and into the low pressure accumulator  144 ,  244  (in fluid communication with the second fluid conduit  134 ,  234  via the control valve  142 ). Applying a rotational force to the output  122 ,  286  using the first hydrostatic unit  114 ,  214  using pressure from the high pressure accumulator  146 ,  246  may be performed, for example, when the driveline  110 ,  210  is accelerating. 
         [0133]    When the driveline  110 ,  210  is placed in the parallel mode of operation, the accumulator assembly  118 ,  218  may be operated in a manner to collect energy from the output  122 ,  286  using the first hydrostatic unit  114 ,  214 . Energy collected from the output  122 ,  286  using the first hydrostatic unit  114 ,  214  is stored in the high pressure accumulator  146 ,  246 . To collect energy from the output  122 ,  286 , the controller  172 ,  298  places the sliding spool  154 ,  254  of the control valve  142 ,  242  in a position that allows fluid communication between the high pressure accumulator  146 ,  246  and the first fluid conduit  130 ,  230 . Based on at least one of the operating condition of the power source  112 ,  212 , the first hydrostatic unit  114 ,  214 , the pressure within each of the accumulators  144 ,  146 ,  244 ,  246 , and the rotational speed of the output  122 ,  286 , the controller  172 ,  298  adjusts a position of the swashplate of the first hydrostatic unit  114 ,  214  to collect energy from the output  122 ,  286  by increasing an amount of fluid stored in the high pressure accumulator  146 ,  246 . Energy from the output  122 ,  286  is used to transfer and increase a pressure of fluid from the second fluid conduit  134 ,  234  (in fluid communication with the low pressure accumulator  144 ,  244 ) to the first fluid conduit  130 ,  230  (in fluid communication with the high pressure accumulator  146 ,  246 ). Collecting energy from the output  122 ,  286  by increasing an amount of fluid stored in the high pressure accumulator  146 ,  246  may be performed, for example, when the driveline  110 ,  210  is decelerating or when a braking of the driveline  110 ,  210  is desired. 
         [0134]    The driveline  110 ,  210  may also be operated in two non-hybrid modes of operation. The non-hybrid modes of operation of the driveline  110 ,  210  may be described as either a low range non-hybrid mode of operation or a high range non-hybrid mode of operation. The low range non-hybrid mode of operation of the driveline  110 ,  210  is characterized by a transfer of power from the power source  112 ,  212  to the output  122 ,  286  via the first hydrostatic unit  114 ,  214 , the fluid conduits  130 ,  134 ,  230 ,  234 , the second hydrostatic unit  116 ,  216 , and the clutching device  120 ,  280 . The high range non-hybrid mode of operation of the driveline  110 ,  210  is characterized by a transfer of power from the power source  112 ,  212  to the output  122 ,  286  via the input  124 ,  282  and the clutching device  120 ,  280 . In either the low range non-hybrid mode of operation or the high range non-hybrid mode of operation of the driveline  110 ,  210 , the sliding spool  154 ,  254  of the control valve  142 ,  242  is placed in a position that does not allow fluid communication between either the low pressure accumulator  144 ,  244  or the high pressure accumulator  146 ,  246  and one of the first fluid conduit  130 ,  230  and the second fluid conduit  134 ,  234 . 
         [0135]    When the driveline  110 ,  210  is placed in the low range non-hybrid mode of operation, the set of clutch teeth of the low range gear  158  are drivingly engaged with the shift collar  160  or the second input clutch  290  is actuated while the first input clutch  288  is disengaged. Accordingly, the output  122 ,  286  is driven by the second hydrostatic unit  116 ,  216  through the low range gear  158  or the second gear portion  297 . The second hydrostatic unit  116 ,  216  is driven using fluid pressure generated by the first hydrostatic unit  114 ,  214  and transferred through the first fluid conduit  130 ,  230  and the second fluid conduit  134 ,  234 . Based on at least one of the operating condition of the power source  112 ,  212 , the first hydrostatic unit  114 ,  214 , the second hydrostatic unit  116 ,  216 , and the rotational speed of the output  122 ,  286 , the controller  172 ,  298  adjusts a position of the swashplate of each of the first hydrostatic unit  114 ,  214  and the second hydrostatic unit  116 ,  216  to apply a rotational force to the output  122 ,  286  using the first hydrostatic unit  114 ,  214  and the second hydrostatic unit  116 ,  216 . 
         [0136]    When the driveline  110 ,  210  is placed in the high range non-hybrid mode of operation, the set of clutch teeth of the high range gear  156  are drivingly engaged with the shift collar  160  or the first input clutch  288  is actuated while the second input clutch  290  is disengaged. Accordingly, the output  122 ,  286  is driven by the input  124 ,  282  through the high range gear  156  or the first gear portion  296 . The controller  172 ,  298  adjusts the operating condition of the power source  112 ,  212  to apply a rotational force to the output  122 ,  286  through the input  124 ,  282  and the high range gear  156  or the first gear portion  296 . 
         [0137]    In use, the driveline  310  may be operated in at least four different hybrid modes of operation. The hybrid modes of operation of the driveline  310  may be described as either series operation or parallel operation. The series operation of the driveline  310  is characterized by a transfer of power from the power source  312  to the output  384  via the first hydrostatic unit  314 , the fluid conduits  387 ,  388 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , and the clutching device  380 . The parallel operation of the driveline  310  is characterized by a transfer of power from the power source  312  to the output  384  via the input  381  and the clutching device  380 . In either the series operation or the parallel operation of the driveline  310 , the accumulator assembly  318  may be operated in a manner to apply a rotational force to the output  384  or collect energy from the output  384  via the first hydrostatic unit  314 , the second hydrostatic unit  316 , and the third hydrostatic unit  317 ; which define the at least four different hybrid modes of operation of the driveline  310 . 
         [0138]    When the driveline  310  is placed in the series mode of operation, at least one of the second input clutch  386  and the clutch and jackshaft assembly  392  is actuated while the first input clutch  385  is disengaged. Accordingly, the output  384  is driven through at least one of the second input gear  386   a  and the third input gear  392   a . As non-limiting examples, the second input gear  386   a  or the third input gear  392   a  may be configured to provide the driveline  310  with a relatively low drive ratio, which may facilitate operation of the driveline  310  during repetitive tasks (such as starting and stopping) or operation of the driveline  310  in confined areas. 
         [0139]    When the driveline  310  is placed in the series mode of operation, the accumulator assembly  318  may be operated in a manner to apply a rotational force to the output  384  using one of the second hydrostatic unit  316  and the third hydrostatic unit  317 . To apply a rotational force to the output  384 , the controller  396  places the sliding spool  354  of the control valve  342  in a position that allows fluid communication between the high pressure accumulator  346  and the first fluid conduit  387 . Based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the pressure within each of the accumulators  344 ,  346 , and the rotational speed of the output  384 , the controller  396  adjusts a position of the swashplate of each of the first hydrostatic unit  314 , and the second hydrostatic unit  316  or the third hydrostatic unit  317  to apply a rotational force to the output  384  using pressure from the high pressure accumulator  346 . Energy stored in the high pressure accumulator  346  is applied to the output  384  through the second hydrostatic unit  316  or the third hydrostatic unit  317  via the first fluid conduit  387 . As a result, fluid passes from the first fluid conduit  387  into the second fluid conduit  388  and into the low pressure accumulator  344  (in fluid communication with the second fluid conduit  388  via the control valve  342 ). Applying a rotational force to the output  384  using the second hydrostatic unit  316  or the third hydrostatic unit  317  using pressure from the high pressure accumulator  346  may be performed, for example, when the driveline  310  is accelerating. 
         [0140]    When the driveline  310  is placed in the series mode of operation, the accumulator assembly  318  may be operated in a manner to collect energy from the output  384  using the second hydrostatic unit  316  or the third hydrostatic unit  317 . Energy collected from the output  384  using the second hydrostatic unit  316  or the third hydrostatic unit  317  is stored in the high pressure accumulator  346 . To collect energy from the output  384 , the controller  396  places the sliding spool  354  of the control valve  342  in a position that allows fluid communication between the high pressure accumulator  346  and the second fluid conduit  388 . Based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , the pressure within each of the accumulators  344 ,  346 , and the rotational speed of the output  384 , the controller  396  adjusts a position of the swashplate of each of the first hydrostatic unit  314  and the second hydrostatic unit  316  or the third hydrostatic unit  317  to collect energy from the output  384  by increasing an amount of fluid stored in the high pressure accumulator  346 . Energy from the output  384  is used to transfer and increase a pressure of fluid from the first fluid conduit  387  (in fluid communication with the low pressure accumulator  344 ) to the second fluid conduit  388  (in fluid communication with the high pressure accumulator  346 ). Collecting energy from the output  384  by increasing an amount of fluid stored in the high pressure accumulator  346  may be performed, for example, when the driveline  310  is decelerating or when a braking of the driveline  310  is desired. 
         [0141]    When the driveline  310  is placed in the parallel mode of operation, the first input clutch  385  is actuated while the second input clutch  386  and the clutch and jackshaft assembly  392  are disengaged. Accordingly, the output  384  is driven through the first input gear  385   a  and the first gear portion  394 . As a non-limiting example, the first input gear  385   a  and the first gear portion  394  may be configured to provide the driveline  310  with a relatively high drive ratio, which may facilitate operation of the driveline  310  during tasks in which the driveline  310  is operated at high speeds, such as when the vehicle the driveline  310  is incorporated in is undergoing acceleration to high speeds or when the vehicle the driveline  310  is incorporated in is moved long distances. 
         [0142]    When the driveline  310  is placed in the parallel mode of operation, the accumulator assembly  318  may be operated in a manner to apply a rotational force to the output  384  using the first hydrostatic unit  314 . To apply a rotational force to the output  384 , the controller  396  places the sliding spool  354  of the control valve  342  in a position that allows fluid communication between the high pressure accumulator  346  and the first fluid conduit  387 . Based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the pressure within each of the accumulators  344 ,  346 , and the rotational speed of the output  384 , the controller  396  adjusts a position of the swashplate of the first hydrostatic unit  314  to apply a rotational force to the output  384  using pressure from the high pressure accumulator  346 . Energy stored in the high pressure accumulator  346  is applied to the output  384  through the first hydrostatic unit  314  via the first fluid conduit  387 . As a result, fluid passes from the first fluid conduit  387  into the second fluid conduit  388  and into the low pressure accumulator  344  (in fluid communication with the second fluid conduit  387  via the control valve  342 ). Applying a rotational force to the output  384  using the first hydrostatic unit  314  using pressure from the high pressure accumulator  346  may be performed, for example, when the driveline  310  is accelerating. 
         [0143]    When the driveline  310  is placed in the parallel mode of operation, the accumulator assembly  318  may be operated in a manner to collect energy from the output  384  using the first hydrostatic unit  314 . Energy collected from the output  384  using the first hydrostatic unit  314  is stored in the high pressure accumulator  346 . To collect energy from the output  384 , the controller  396  places the sliding spool  354  of the control valve  342  in a position that allows fluid communication between the high pressure accumulator  346  and the first fluid conduit  387 . Based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the pressure within each of the accumulators  344 ,  346 , and the rotational speed of the output  384 , the controller  396  adjusts a position of the swashplate of the first hydrostatic unit  114 ,  214  to collect energy from the output  384  by increasing an amount of fluid stored in the high pressure accumulator  346 . Energy from the output  384  is used to transfer and increase a pressure of fluid from the second fluid conduit  388  (in fluid communication with the low pressure accumulator  344 ) to the first fluid conduit  387  (in fluid communication with the high pressure accumulator  346 ). Collecting energy from the output  384  by increasing an amount of fluid stored in the high pressure accumulator  346  may be performed, for example, when the driveline  310  is decelerating or when a braking of the driveline  310  is desired. 
         [0144]    The driveline  310  may also be operated in two non-hybrid modes of operation. The non-hybrid modes of operation of the driveline  310  may be described as either a low range non-hybrid mode of operation or a high range non-hybrid mode of operation. The low range non-hybrid mode of operation of the driveline  310  is characterized by a transfer of power from the power source  312  to the output  384  via the first hydrostatic unit  314 , the fluid conduits  387 ,  388 , the second hydrostatic unit  316  or the third hydrostatic unit  317 , and the clutching device  380 . The high range non-hybrid mode of operation of the driveline  310  is characterized by a transfer of power from the power source  312  to the output  384  via the input  381  and the clutching device  380 . In either the low range non-hybrid mode of operation or the high range non-hybrid mode of operation of the driveline  310 , the sliding spool  354  of the control valve  342  is placed in a position that does not allow fluid communication between either the low pressure accumulator  344  or the high pressure accumulator  346  and one of the first fluid conduit  387  and the second fluid conduit  388 . 
         [0145]    When the driveline  310  is placed in the low range non-hybrid mode of operation, one of the second input clutch  386  and the clutch and jackshaft assembly  392  is actuated while the first input clutch  288  is disengaged. Accordingly, the output  384  is driven by either the second hydrostatic unit  316  through the second input gear  386   a  and the second gear portion  395  or the third hydrostatic unit  317  through the third input gear  392   a  and the second gear portion  395 . The second hydrostatic unit  316  and the third hydrostatic unit  317  are each driven using fluid pressure generated by the first hydrostatic unit  314  and transferred through the first fluid conduit  387  and the second fluid conduit  388 . Based on at least one of the operating condition of the power source  312 , the first hydrostatic unit  314 , the second hydrostatic unit  316 , the third hydrostatic unit  317 , and the rotational speed of the output  384 , the controller  396  adjusts a position of the swashplate of each of the first hydrostatic unit  314  and the second hydrostatic unit  316  or the third hydrostatic unit  317  to apply a rotational force to the output  384  using the first hydrostatic unit  314  and the second hydrostatic unit  316  or the third hydrostatic unit  317 . 
         [0146]    When the driveline  310  is placed in the high range non-hybrid mode of operation, the first input clutch  385  is actuated while each of the second input clutch  386  and the clutch and jackshaft assembly  392  are disengaged. Accordingly, the output  384  is driven by the input  381  through the first input gear  385   a  and the first gear portion  394 . The controller  396  adjusts the operating condition of the power source  312  to apply a rotational force to the output  384  through the input  381  and the first input gear  385   a  and the first gear portion  394 . 
         [0147]    The accumulator assembly  118 ,  218 ,  318  may be used to facilitate shifting the driveline  110 ,  210 ,  310  from the series mode of operation to the parallel mode of operation or from the parallel mode of operation to the series mode of operation. During the shifting of the driveline  110 ,  210 ,  310 , the accumulator assembly  118 ,  218 ,  318  may be operated in a manner to collect energy from the driveline  110 ,  210 ,  310  and place the second hydrostatic unit  116 ,  216 ,  316  or the third hydrostatic unit  317  in a condition that facilitates shifting the driveline  110 ,  210 ,  310  from the series mode of operation to the parallel mode of operation or the accumulator assembly  118 ,  218 ,  318  may be operated in a manner to place the second hydrostatic unit  116 ,  216 ,  316  or the third hydrostatic unit  317  in a condition that facilitates shifting the driveline  110 ,  210 ,  310  from the parallel mode of operation to the series mode of operation. 
         [0148]    The accumulator assembly  118 ,  218 ,  318  may be used to facilitate shifting the driveline  110 ,  210 ,  310  from the series mode of operation to the parallel mode of operation. During a shifting procedure from the series mode to the parallel mode, the accumulator assembly  118 ,  218 ,  318  may be operated in a manner to collect energy from the driveline  110 ,  210 ,  310  and place the second hydrostatic unit  116 ,  216 ,  316  or the third hydrostatic unit  317  in a condition that facilitates the shifting procedure. 
         [0149]      FIGS. 4A through 4F  illustrate the shifting procedure for the driveline  110  from the series mode to the parallel mode as a series of steps over a given time period. It is understood that the shifting procedure for the driveline  110  may be adapted for the other embodiments of the driveline  210 ,  310  described herein and illustrated in  FIGS. 2 and 3  using similar principles of operation. The given time period for the shifting procedure is represented on each of the horizontal axes of  FIGS. 4A through 4F , and is divided into six periods of time in which the steps necessary to complete the shift are performed. The vertical axes of  FIGS. 4A through 4F  respectively represent a velocity of the vehicle the driveline  110  is incorporated in, a rotational speed of the second hydrostatic unit  116 , a rotational speed of the power source  112 , a displacement of the second hydrostatic unit  116 , an amount of torque applied by the power source  112 , and a position of the clutching device  120 . 
         [0150]    The shifting procedure for the driveline  110  from the series mode to the parallel mode may be initiated when the driveline  110  is being operated at or near a maximum velocity of the series mode of the vehicle when the clutching device  120  is in the second position. As described hereinabove, in the second position the shift collar  160  is drivingly engaged with the set of clutch teeth of the low range gear  158  and the set of output gear teeth  170  of the output  122 . As shown in  FIG. 4A , the driveline  110  is being operated at or near a maximum velocity of the series mode when the clutching device  120  is in the second position of the vehicle during the time period labeled “1”. 
         [0151]    Next, to facilitate disengagement of the shift collar  160  from the set of clutch teeth of the low range gear  158 , an amount of torque applied by the second hydrostatic unit  116  to the low range gear  158  is reduced to a low or about zero value. The amount of torque applied by the second hydrostatic unit  116  to the low range gear  158  is reduced by adjusting a displacement of the second hydrostatic unit  116 . In response to a command by the controller  172 , the swashplate of the second hydrostatic unit  116  is positioned to adjust a displacement of the second hydrostatic unit  166  so that an amount of torque applied by the second hydrostatic unit  116  is reduced to a low or about zero value. As shown in  FIG. 4D , the displacement of the second hydrostatic unit  116  is reduced to a low or about zero value during the time period labeled “2,” thereby reducing an amount of torque applied by the second hydrostatic unit  116  to a low or substantially equal to zero amount. Once the amount of torque applied by the second hydrostatic unit  116  is reduced to a low or about zero value, the controller  172  disengages the shift collar  160  from the low range gear  158 , placing the clutching device  120  in the neutral position. 
         [0152]    Also during the time period labeled “2”, fluid pumped by the first hydrostatic unit  114  is diverted to the high pressure accumulator  146  of the accumulator assembly  118  to accommodate for the reduced amount of displacement of the second hydrostatic unit  116 . Accordingly, a pressure within the high pressure accumulator  146  is increased. 
         [0153]    Next, in response to the clutching device  120  being placed in the neutral position, a velocity of the vehicle the driveline  110  is incorporated in may begin to decrease, as the output  122  is drivingly disengaged from both the low range gear  158  and the high range gear  156 . As shown in  FIG. 4A , the vehicle the driveline  110  is incorporated in may begin to decrease in velocity during the time period labeled “3”. 
         [0154]    Next, to facilitate synchronization between the output  122  and the high range gear  156 , and consequently engagement of the shift collar  160  with the set of clutch teeth of the high range gear  156 , an amount of torque applied by the power source  112  through the first hydrostatic unit  114  to the high range gear  156  may be adjusted to a low or about zero value. The amount of torque applied by the power source  112  to the high range gear  156  may be adjusted by changing a rotational speed of the power source  112 . In response to a command by the controller  172 , a rotational speed of the power source  112  may be adjusted so that an amount of torque applied by the power source  112  is reduced to a low or about zero value. As non-limiting examples, a rotational speed of the power source  112  may be adjusted by adjusting a rate of fuel delivery to the power source  112  or by adjusting a level of engagement of a clutching device (not shown) forming a portion of the power source  112 . As shown in  FIG. 4E , the amount of torque applied by the power source  112  is reduced to a low or about zero value during the time periods labeled “2”, “3”, and “4”. A rotational speed of the power source  112  is adjusted during the time periods labeled “2”, “3”, and “4” to be synchronized with a rotational speed of the output  122 , as shown in  FIG. 4C . Once synchronization between the output  122  and the high range gear  156  has occurred, the controller  172  engages the shift collar  160  with the high range gear  156 , placing the clutching device  120  in the first position, as shown in  FIG. 4F , during the time period labeled “4”. 
         [0155]    Once the clutching device  120  is placed in the first position, the shifting procedure for the driveline  110  from the series mode to the parallel mode is completed. Following completion of the shifting procedure, torque may be applied by the power source  112  to the output  122  through the high range gear  156  and the shift collar  160 . As non-limiting examples, torque may be applied by the power source  112  to the output  122  by adjusting a rate of fuel delivery to the power source  112  or by adjusting a level of engagement of a clutching device (not shown) forming a portion of the power source  112 . As a result of torque being applied by the power source  112  to the output  122 , a rotational speed of the power source  112  is increased and a velocity of the vehicle the driveline  110  is incorporated in is increased, as shown in  FIGS. 4A and 4C , during the time period labeled “5”. Acceleration of the vehicle the driveline  110  is incorporated in may continue when the clutching device  120  is in the first position until the vehicle is operating at or near a maximum velocity of the vehicle, as shown in  FIG. 4A , during the time period labeled “6”. 
         [0156]    The accumulator assembly  118 ,  218 ,  318  may be used to facilitate shifting the driveline  110 ,  210 ,  310  from the parallel mode of operation to the series mode of operation. During a shifting procedure from the parallel mode to the series mode, the accumulator assembly  118 ,  218 ,  318  may be operated in a manner to place the second hydrostatic unit  116 ,  216 ,  316  or the third hydrostatic unit  317  in a condition that facilitates the shifting procedure. 
         [0157]      FIGS. 5A through 5F  illustrate the shifting procedure for the driveline  110  from the parallel mode to the series mode as a series of steps over a given time period. It is understood that the shifting procedure for the driveline  110  may be adapted for the other embodiments of the driveline  210 ,  310  described herein and illustrated in  FIGS. 2 and 3  using similar principles of operation. The given time period for the shifting procedure is represented on each of the horizontal axes of  FIGS. 5A through 5F , and is divided into six periods of time in which the steps necessary to complete the shift are performed. The vertical axes of  FIGS. 5A through 5F  respectively represent a velocity of the vehicle the driveline  110  is incorporated in, a rotational speed of the second hydrostatic unit  116 , a rotational speed of the power source  112 , a displacement of the second hydrostatic unit  116 , an amount of torque applied by the power source  112 , and a position of the clutching device  120 . 
         [0158]    The shifting procedure for the driveline  110  from the parallel mode to the series mode occurs may be initiated when the driveline  110  is being operated at or near a minimum velocity of the vehicle when the clutching device  120  is in the first position. As described hereinabove, in the first position the shift collar  160  is drivingly engaged with the set of clutch teeth of the high range gear  156  and the set of output gear teeth  170  of the output  122 . As shown in  FIG. 5A , the driveline  110  is being operated at or near a minimum velocity of the vehicle when the clutching device  120  is in the first position during the time period labeled “2”. 
         [0159]    Next, to facilitate disengagement of the shift collar  160  from the set of clutch teeth of the high range gear  156 , an amount of torque applied by the power source  112  to the high range gear  156  is reduced to a low or about zero value. The amount of torque applied by the power source  112  to the high range gear  156  may be adjusted by changing a rotational speed of the power source  112 . In response to a command by the controller  172 , a rotational speed of the power source  112  may be adjusted so that an amount of torque applied by the power source  112  is reduced to a low or about zero value. As non-limiting examples, a rotational speed of the power source  112  may be adjusted by adjusting a rate of fuel delivery to the power source  112  or by adjusting a level of engagement of a clutching device (not shown) forming a portion of the power source  112 . As shown in  FIG. 5E , the amount of torque applied by the power source  112  is reduced to a low or about zero value during the time period labeled “3”. Once the amount of torque applied by the power source  112  is reduced to a low or about zero value, the controller  172  disengages the shift collar  160  from the high range gear  156 , placing the clutching device  120  in the neutral position. 
         [0160]    Next, in response to the clutching device  120  being placed in the neutral position, a velocity of the vehicle the driveline  110  is incorporated in may begin to decrease, as the output  122  is drivingly disengaged from both the low range gear  158  and the high range gear  156 . As shown in  FIG. 5A , the vehicle the driveline  110  is incorporated in may begin to decrease in velocity during the time period labeled “3”. 
         [0161]    Also during the time period labeled “3”, fluid from the high pressure accumulator  146  of the accumulator assembly  118  is diverted to the second hydrostatic unit  116 , increasing a rotational speed thereof. Further, a displacement of the second hydrostatic unit  116  is adjusted to facilitate an adjustment of the rotational speed thereof. In response to a command by the controller  172 , the swashplate of the second hydrostatic unit  116  is positioned to adjust a displacement of the second hydrostatic unit  116  (and thus the low range gear  158 ) so that a rotational speed is increased to value that facilitates synchronization and engagement between the low range gear  158  and the output  122 . 
         [0162]    Once synchronization between the output  122  and the low range gear  158  has occurred, the controller  172  engages the shift collar  160  with the low range gear  158 , placing the clutching device  120  in the second position, as shown in  FIG. 5F , during the time period labeled “4”. 
         [0163]    Once the clutching device  120  is placed in the second position, the shifting procedure for the driveline  110  from the parallel mode to the series mode is completed. Following completion of the shifting procedure, torque may be applied by the power source  112  to the output  122  through the first hydrostatic unit  114 , the first fluid conduit  130 , the second hydrostatic unit  116 , the low range gear  158 , and the shift collar  160 . As a result of torque being applied by the power source  112  to the output  122 , a rotational speed of the power source  112  remains substantially constant and a velocity of the vehicle the driveline  110  is incorporated in may be further decreased, as shown in  FIGS. 5A and 5C , during the time period labeled “5”. Deceleration of the vehicle the driveline  110  is incorporated in may continue when the clutching device  120  is in the second position until the vehicle is operating at or near a minimum velocity of the vehicle, as shown in  FIG. 5A , during the time period labeled “6”. 
         [0164]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope. 
         [0000]    The present subject-matter includes, inter alia, the following aspects:
 
1. A hybrid driveline for a vehicle which may be operated in a hydrostatic drive mode and a direct drive mode, the hybrid driveline comprising:
 
         [0165]    a power source; 
         [0166]    a first hydrostatic unit drivingly engaged with the power source; 
         [0167]    a second hydrostatic unit selectively drivingly engaged with a vehicle output, the second hydrostatic unit in fluid communication with the first hydrostatic unit; 
         [0168]    an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit; and 
         [0169]    a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit, wherein the hybrid driveline is operated in the hydrostatic drive mode by drivingly engaging the second hydrostatic unit with the vehicle output using the clutching device and the hybrid driveline is operated in the direct drive mode by drivingly engaging the power source with the vehicle output using the clutching device. 
         [0000]    2. The hybrid driveline according to aspect  1 , wherein the accumulator assembly comprises a low pressure accumulator, a high pressure accumulator, and at least one control valve.
 
3. The hybrid driveline according to aspect  2 , wherein the at least one control valve has at least a first position and a second position, the at least one control valve in the first position facilitating fluid communication between the high pressure accumulator and a first fluid conduit in fluid communication with the first hydrostatic unit and the at least one control valve in the second position facilitating fluid communication between the high pressure accumulator and a second fluid conduit in fluid communication with the first hydrostatic unit and the second hydrostatic unit.
 
4. The hybrid driveline according to aspect  1 , wherein the clutching device comprises a shift collar, a first synchronizer, and a second synchronizer.
 
5. The hybrid driveline according to aspect  1 , wherein the clutching device comprises a shift collar, a first synchronizer, and a second synchronizer; the first synchronizer facilitating synchronization engagement between the first hydrostatic unit and the vehicle output and the second synchronizer facilitating synchronization between the second hydrostatic unit and the vehicle output.
 
6. The hybrid driveline according to aspect  1 , wherein the clutching device comprises a first clutch and a second clutch; the first clutch facilitating variable driving engagement between the first hydrostatic unit and the vehicle output and the second clutch facilitating variable driving engagement between the second hydrostatic unit and the vehicle output.
 
7. The hybrid driveline according to aspect  6 , wherein the first clutch and the second clutch are each wet plate style clutches.
 
8. The hybrid driveline according to aspect  1 , wherein the clutching device comprises a low range gear and a high range gear, the low range gear in driving engagement with the second hydrostatic unit and the vehicle output when the hybrid driveline is operated in the hydrostatic drive mode and the high range gear in driving engagement with the first hydrostatic unit and the vehicle output when the hybrid driveline is operated in the direct drive mode.
 
9. The hybrid driveline according to aspect  1 , further comprising a third hydrostatic unit which may be selectively drivingly engaged with a vehicle output, the third hydrostatic unit in fluid communication with the first hydrostatic unit and the accumulator assembly.
 
10. The hybrid driveline according to aspect  9 , wherein the clutching device comprises a first clutch, a second clutch, and a third clutch; the first clutch facilitating variable driving engagement between the first hydrostatic unit and the vehicle output, the second clutch facilitating variable driving engagement between the second hydrostatic unit and the vehicle output, and the third clutch facilitating variable driving engagement between the third hydrostatic unit and the vehicle output.
 
11. The hybrid driveline according to aspect  10 , wherein the first clutch, the second clutch, and the third clutch are each wet plate style clutches.
 
12. A method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode, the method comprising the steps of:
 
         [0170]    providing a power source; 
         [0171]    providing a first hydrostatic unit drivingly engaged with the power source; 
         [0172]    providing a second hydrostatic unit selectively drivingly engaged with a vehicle output, the second hydrostatic unit in fluid communication with the first hydrostatic unit; 
         [0173]    providing an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit; 
         [0174]    providing a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit; 
         [0175]    drivingly engaging the second hydrostatic unit with the vehicle output using the clutching device to place the hybrid driveline in the hydrostatic drive mode; and 
         [0176]    drivingly engaging the power source with the vehicle output using the clutching device to place the hybrid driveline in the direct drive mode. 
         [0000]    13. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to aspect  12 , wherein the accumulator assembly comprises a low pressure accumulator, a high pressure accumulator, and at least one control valve.
 
14. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to aspect  13 , further comprising the step of placing the at least one control valve in one of a first position and a second position, the at least one control valve in the first position facilitating fluid communication between the high pressure accumulator and a first fluid conduit in fluid communication with the first hydrostatic unit and the at least one control valve in the second position facilitating fluid communication between the high pressure accumulator and a second fluid conduit in fluid communication with the first hydrostatic unit and the second hydrostatic unit.
 
15. The method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode according to aspect  14 , further comprising the step of applying a rotational force to the vehicle output using one of the first hydrostatic unit and the second hydrostatic unit in fluid communication with the high pressure accumulator and/or
 
         [0177]    further comprising the step of collecting energy from the vehicle output using one of the first hydrostatic unit and the second hydrostatic unit in fluid communication with the high pressure accumulator and storing the energy in the high pressure accumulator and/or 
         [0178]    further comprising the step of collecting energy from the power source using the first hydrostatic unit in fluid communication with the high pressure accumulator and storing the energy in the high pressure accumulator to facilitate shifting from the hydrostatic drive mode to the direct drive mode and/or 
         [0179]    further comprising the step of applying a rotational force to the second hydrostatic unit using with the high pressure accumulator to facilitate shifting from the direct drive mode to the hydrostatic drive mode.