Abstract:
A combined hybrid drive system and electro-hydraulic machine includes a hybrid drive system that is adapted to decelerate a rotatably driven mechanism, accumulate the energy resulting from such deceleration, and use the accumulated energy to subsequently accelerate the rotatably driven mechanism. An electro-hydraulic machine is operatively connected to the hybrid drive system and is adapted to be operated in one or more of a plurality of modes to improve the performance of the hybrid drive system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/022,926 filed Jan. 23, 2008, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates in general to hybrid drive systems for vehicles and other mechanisms. In particular, this invention relates to an electro-hydraulic machine for use with such a hybrid drive system. 
         [0003]    Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source of rotational power to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine generates rotational power, and such rotational power is transferred from an output shaft of the engine through a driveshaft to an input shaft of an axle so as to rotatably drive the wheels of the vehicle. 
         [0004]    In some vehicles and other mechanisms, a hybrid drive system is provided in conjunction with the drive train system for accumulating energy during braking of the rotatably driven mechanism and for using such accumulated energy to assist in subsequently rotatably driving the rotatably driven mechanism. To accomplish this, a typical hybrid drive system includes an energy storage device and a reversible energy transfer machine. The reversible energy transfer machine communicates with the energy storage device and is mechanically coupled to a portion of the drive train system. Typically, the hybrid drive system can be operated in either a retarding mode, a neutral mode, or a driving mode. In the retarding mode, the reversible energy transfer machine of the hybrid drive system accumulates energy by braking or otherwise retarding the rotatably driven mechanism of the drive train system and stores such energy in the energy storage device. In the neutral mode, the hydraulic drive system is disconnected from the drive train system and, therefore, is substantially inoperative to exert any significant driving or retarding influence on the rotatably driven mechanism. In the driving mode, the reversible energy transfer machine of the hybrid drive system supplies the accumulated energy previously stored in the energy storage device to assist in subsequently rotatably driving the rotatably driven mechanism. 
         [0005]    One commonly known hybrid drive system uses pressurized fluid as the actuating mechanism. In such a hydraulic hybrid drive system, a fluid energy storage device (such as an accumulator) and a reversible hydraulic machine are provided. Another commonly known hybrid drive system uses electricity as the actuating mechanism. In such an electric hybrid drive system, an electrical energy storage device (such as a battery) and a reversible electric machine are provided. Other hybrid drive systems are known in the art that use other actuating mechanisms. 
         [0006]    Regardless of the specific actuating mechanism that is used, the hybrid drive system can improve the performance of the drive train system (such as fuel economy, for example) by recovering and storing energy during deceleration and by retrieving and supplying the stored energy for use during a subsequent acceleration. However, the hybrid drive system does not improve the performance of the drive train system during idle situations, such as when a vehicle in which the drive train system is provided is not moving. During such idle situations, the performance of the drive train system can be improved by turning off the engine. However, the drive train system may include one or more accessories that may be necessary or desirable to be operated while the engine is not operated. Such accessories can be electrically operated (such as lighting systems, navigation systems, audio systems, and the like), hydraulically operated (such as steering systems, braking systems, air conditioning systems, and the like), or a combination thereof. Thus, it would be desirable to provide an improved structure for a hybrid drive system that is capable of operating such accessories while the engine is not operated. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention relates to a combined hybrid drive system and electro-hydraulic machine. The hybrid drive system is adapted to decelerate a rotatably driven mechanism, accumulate the energy resulting from such deceleration, and use the accumulated energy to subsequently accelerate the rotatably driven mechanism. The electro-hydraulic machine is operatively connected to the hybrid drive system and is adapted to be operated in one or more of a plurality of modes to improve the performance of the hybrid drive system. 
         [0008]    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  
         [0009]    The sole FIGURE is a schematic diagram of a drive train system including a hybrid drive system and an electro-hydraulic machine in accordance with this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    Referring now to the drawings, there is illustrated in  FIG. 1  a drive train system, indicated generally at  10 , for generating power from a source and for transferring such power from the source to a driven mechanism. The illustrated drive train system  10  is a vehicular drive train system that includes an engine  11  that generates rotational power to an axle assembly  12  by means of a hybrid drive system, indicated generally at  20 . However, the illustrated vehicle drive train system  10  is intended merely to illustrate one environment in which this invention may be used. Thus, the scope of this invention is not intended to be limited for use with the specific structure for the vehicular drive train system  10  illustrated in  FIG. 1  or with vehicle drive train systems in general. On the contrary, as will become apparent below, this invention may be used in any desired environment for the purposes described below. 
         [0011]    The illustrated hybrid drive system  20  includes a power drive unit  21  that is connected between the engine  11  and the axle assembly  12 . The illustrated power drive unit  21  is, in large measure, conventional in the art and is intended merely to illustrate one environment in which this invention may be used. Thus, the scope of this invention is not intended to be limited for use with the specific structure for the power drive unit  21  illustrated in  FIG. 1 . The illustrated power drive unit  21  includes an input shaft  22  that is rotatably driven by the engine  11 . An input gear  23  is supported on the input shaft  22  for rotation therewith. The input gear  23  is connected for rotation with a primary pump drive gear  24  that, in turn, is connected for rotation with an input shaft of a primary pump  25 . Thus, the primary pump  25  is rotatably driven whenever the engine  11  is operated. The purpose of the primary pump  25  will be explained below. 
         [0012]    The illustrated power drive unit  21  also includes a main drive clutch  26  that selectively connects the input shaft  22  to an output shaft  27 . When the main drive clutch  26  is engaged, the input shaft  22  is connected for rotation with the output shaft  27 . When the main drive clutch  26  is disengaged, the input shaft  22  is not connected for rotation with the output shaft  27 . The output shaft  27  is connected for rotation with an input shaft of the axle assembly  12 . Thus, the axle assembly  12  is rotatably driven by the engine  11  whenever the main drive clutch  26  is engaged. 
         [0013]    The illustrated power drive unit  21  further includes a low drive clutch  30  that selectively connects the output shaft  27  to a low drive clutch gear  31 . The low drive clutch output gear  31  is connected for rotation with both a first low drive output gear  32  and a second low drive output gear  33 . The first low drive output gear  32  is connected for rotation with a first shaft  32   a  that, in turn, is connected for rotation with an input shaft of a first pump/motor  34 . Similarly, the second low drive output gear  33  is connected for rotation with a second shaft  33   a  that, in turn, is connected for rotation with an input shaft of a second pump/motor  35 . Thus, when both the main drive clutch  26  and the low drive clutch  30  are engaged, the output shaft  27  rotatably drives both the first pump/motor  34  and the second pump motor  35 . The purpose for both the first pump/motor  34  and the second pump motor  35  will be explained below. 
         [0014]    Similarly, the illustrated power drive unit  21  further includes a high drive clutch  36  that selectively connects the output shaft  27  to a high drive clutch gear  37 . The high drive clutch output gear  37  is connected for rotation with both a first high drive output gear  38  and a second high drive output gear  39 . The first high drive output gear  38  is connected for rotation with the first shaft  32   a  that, as mentioned above, is connected for rotation with the input shaft of the first pump/motor  34 . Similarly, the second high drive output gear  39  is connected for rotation with the second shaft  33   a  that, as also mentioned above, is connected for rotation with the input shaft of the second pump/motor  35 . Thus, when both the main drive clutch  26  and the high drive clutch  36  are engaged, the output shaft  27  rotatably drives both the first pump/motor  34  and the second pump motor  35 . The low drive gears  31 ,  32 , and  33  are selected to provide a relatively low gear ratio when the main drive clutch  26  and the low drive clutch  30  are engaged, in comparison with the relatively high gear ratio provided by the high drive gears  37 ,  28 , and  39  when the main drive clutch  26  and the high drive clutch  36  are engaged. 
         [0015]    The illustrated power drive unit  21  also includes an accumulator  40  or similar relatively high fluid pressure storage device. The accumulator  40  selectively communicates with a first port of the primary pump  25  through a primary pump valve  41 . The primary pump valve  41  is conventional in the art and can be operated in a first position (shown in  FIG. 1 ), wherein fluid communication from the accumulator  40  to the first port of the primary pump  25  is prevented and fluid communication from the first port of the primary pump  25  to the accumulator  40  is permitted. However, the primary pump valve  41  can be operated in a second position (to the right when viewing  FIG. 1 ), wherein fluid communication from the accumulator  40  to the first port of the primary pump  25  is permitted and fluid communication from the first port of the primary pump  25  to the accumulator  40  is permitted. For the purposes of this invention, the primary pump valve  41  is always maintained in the illustrated first position, wherein fluid communication from the accumulator  40  to the first port of the primary pump  25  is prevented and fluid communication from the first port of the primary pump  25  to the accumulator  40  is permitted. 
         [0016]    The accumulator  40  also selectively communicates with a first port of the first pump/motor  34  through a first control valve  42 . The first control valve  42  is conventional in the art and can be operated in a first position (shown in  FIG. 1 ), wherein fluid communication from the first port of the first pump/motor  34  to the accumulator  40  is permitted and fluid communication from the accumulator  40  to the first port of the first pump/motor  34  is prevented. However, the first control valve  42  can be operated in a second position (to the right when viewing  FIG. 1 ), wherein fluid communication from the first port of the first pump/motor  34  to the accumulator  40  is permitted and fluid communication from the accumulator  40  to the first port of the first pump/motor  34  is permitted. 
         [0017]    The accumulator  40  further selectively communicates with a first port of the second pump/motor  35  through a second control valve  43 . The second control valve  43  is conventional in the art and can be operated in a first position (shown in  FIG. 1 ), wherein fluid communication from the first port of the second pump/motor  35  to the accumulator  40  is permitted and fluid communication from the accumulator  40  to the first port of the second pump/motor  35  is prevented. However, the second control valve  43  can be operated in a second position (to the right when viewing  FIG. 1 ), wherein fluid communication from the first port of the second pump/motor  35  to the accumulator  40  is permitted and fluid communication from the accumulator  40  to the first port of the second pump/motor  35  is permitted. 
         [0018]    The illustrated power drive unit  21  further includes a reservoir  44  or similar relatively low fluid pressure storage device. Each of the primary pump  25 , the first pump/motor  34 , and the second pump/motor  35  includes a second port, and all of such second ports communicate with the reservoir  44  to draw fluid therefrom when necessary, as described below. 
         [0019]    The basic operation of the drive train system  10  will now be described. When the engine  11  of the drive train system  10  is initially started, the main drive clutch  26 , the low drive clutch  30 , and the high drive clutch  36  are all disengaged, and the valves  41 ,  42 , and  43  are all in their first positions illustrated in  FIG. 1 . In this initial condition, the engine  11  rotatably drives the primary pump  25  through the input shaft, the input gear  23 , and the primary pump drive gear  24 , as described above. As a result, the primary pump  25  draws fluid from the reservoir  44  through the second port thereof, and further supplies such fluid under pressure from the first port of the primary pump  25  through the primary pump valve  41  to the accumulator  40 . As discussed above, the first and second control valves  42  and  43  prevent the pressurized fluid from the primary pump  25  or the accumulator  40  from being supplied to the first ports of the first and second pump/motors  34  and  35 , respectively. Such initially operation continues until a sufficient amount of such pressurized fluid has been supplied to the accumulator  40 . Because the main drive clutch  26 , the low drive clutch  30 , and the high drive clutch  36  are all disengaged, the engine  11  does not rotatably drive the output shaft  27  or the axle assembly  12  in this initial operation of the drive train system  10 . 
         [0020]    When it is desired to move the vehicle, the low drive clutch  30  is engaged, while the main drive clutch  26  and the high drive clutch  36  remain disengaged. As a result, the output shaft  27  is connected to the low drive clutch gear  31  for concurrent rotation. At the same time, the first control valve  42  and the second control valve  43  are each moved to their second positions. This permits pressurized fluid from the accumulator  40  to flow to the first ports of both the first pump/motor  34  and the second pump/motor  35 . Lastly, the first and second pump/motors  34  and  35  are each placed in a positive displacement mode, wherein they function as motors to use the pressurized fluid supplied by the accumulator  40  to rotatably drive the first and second shafts  32   a  and  33   a.  In turn, this causes the low drive gears  31 ,  32 , and  33  and the output shaft  27  to be rotatably driven. As a result, the axle assembly  12  is rotatably driven at the relatively low gear ratio provided by the low drive gears  31 ,  32 , and  33 . Such a relatively low gear ratio is well suited for providing the relatively high torque needed to accelerate the vehicle from a standstill. 
         [0021]    Once it has begun to move, it may be desirable to move the vehicle at a higher speed that is suitable for the relatively low gear ratio provided by the low drive gears  31 ,  32 , and  33 . In this instance, the power drive unit  21  can be operated to disengage the low drive clutch  30  and engage the high drive clutch  36 , while maintaining the main drive clutch  26  disengaged. As a result, the output shaft  27  is connected to the high drive clutch output gear  37  for concurrent rotation. The first control valve  42  and the second control valve  43  are each moved to (or maintained in) their second positions. As described above, this permits pressurized fluid from the accumulator  40  to flow to the first ports of both the first pump/motor  34  and the second pump/motor  35 . As also described above, the first and second pump/motors  34  and  35  are each placed (or maintained) in a positive displacement mode, wherein they function as motors to use the pressurized fluid supplied by the accumulator  40  to rotatably drive the first and second shafts  32   a  and  33   a.  In turn, this causes the high drive gears  37 ,  38 , and  39  and the output shaft  27  to be rotatably driven. As a result, the axle assembly  12  is rotatably driven at the relatively low gear ratio provided by the high drive gears  37 ,  38 , and  39 . Such a relatively high gear ratio is well suited for providing the relatively low torque needed to accelerate the vehicle to a relatively high speed. 
         [0022]    If it is desired to operate the vehicle at a further higher speed, the power drive unit  21  can be operated to disengage the high drive clutch  36  and engage the main drive clutch  26 , while the low drive clutch  30  remains disengaged. As a result, the output shaft  27  is connected to the input shaft  22  for concurrent rotation. At the same time, the first control valve  42  and the second control valve  43  are each moved to their first positions. As described above, this prevents pressurized fluid from the accumulator  40  from flowing to the outputs of both the first pump/motor  34  and the second pump/motor  35 . As a result, the first and second pump/motors  34  and  35  are isolated from the drive train system  10 . 
         [0023]    Under certain circumstances, the above-described components of the hybrid drive system  20  can also be used to slow or stop the movement of the vehicle. To accomplish this, the main drive clutch  26  and the low drive clutch  30  are disengaged, while the high drive clutch  36  is engaged (in some instances, it may be preferable that the main drive clutch  26  and the high drive clutch  36  be disengaged, while the low drive clutch  30  is engaged). Regardless, the first control valve  42  and the second control valve  43  are each moved to (or maintained in) their second positions. This permits pressurized fluid from the first ports of both the first pump/motor  34  and the second pump/motor  35  to flow to the accumulator  40 . Lastly, the first and second pump/motors  34  and  35  are each placed in a negative displacement mode, wherein they function as pumps to use the rotational energy of the rotating output shaft  27  to supply pressurized fluid to the accumulator  40 . As a result, the output shaft  27  rotates the high drive gears  37 ,  38 , and  39 , which causes the first pump/motor  34  and the second pump/motor  35  to be rotatably driven. Consequently, the rotation of the axle assembly  12  is decelerated as the kinetic energy thereof is stored as fluid pressure in the accumulator  40 . 
         [0024]    It is often desirable to provide a separate brake system to affirmatively slow or stop the rotation of the axle assembly  12 . As shown in  FIG. 1 , such a separate brake system is provided within the axle assembly  12  of the illustrated drive train system  10  as a pair of friction brakes  45  associated with respective wheels of the vehicle. The friction brakes  45  are conventional in the art and may be actuated in any desired manner, such as pneumatically or hydraulically. 
         [0025]    In the illustrated hybrid drive system  20 , pressurized fluid is used as the actuating mechanism. In such a hydraulic hybrid drive system, the accumulator  40  functions as the energy storage device, and the pump/motors  34  and  35  function as reversible hydraulic machines. Another commonly known hybrid drive system uses electricity as the actuating mechanism. In such an electric hybrid drive system, an electrical energy storage device (such as a capacitor or a battery) and a reversible electrical machine (such as generator/motor) are provided and function in a similar manner as described above. This invention is not intended to be limited to the specific structure of the hybrid drive system, but rather is intended to cover any similar structures. 
         [0026]    The illustrated hybrid drive system  20  further includes an electro-hydraulic machine, indicated generally at  50 , in accordance with this invention. The illustrated electro-hydraulic machine  50  includes an input shaft  51  that is connected for rotation with the input shaft  22  of the power drive unit  21  that, as described above, can be rotatably driven by the engine  11 . In the illustrated embodiment, the input shaft  51  of the clutch  55  is connected for rotation with the input shaft  22  of the power drive unit  21  by a first pulley  52   a,  a belt  52   b,  and a second pulley  52   c.  The first pulley  52   a  is mounted on or otherwise connected for rotation with the input shaft  22  of the power drive unit  21 . The second pulley  52   c  is mounted on or otherwise connected for rotation with the input shaft  51  of the electro-hydraulic machine  50 . The belt  52   b  extends about the first pulley  52   a  and the second pulley  52   c  such that the first and second pulleys  52   a  and  52   c  are connected for rotation together. In this manner, the input shaft  51  of the electro-hydraulic machine  50  is connected for rotation with the input shaft  22  of the power drive unit  21 . However, the input shaft  51  of the clutch  55  can connected for rotation with the input shaft  22  of the power drive unit  21  by any desired structure including, for example, gears, shafts or a direct drive arrangement. 
         [0027]    The input shaft  51  of the electro-hydraulic machine  50  is selectively connected through a clutch  53  to an output shaft  54  of the electro-hydraulic machine  50 . The clutch  53  is conventional in the art and is adapted to selectively connect the input shaft  51  for rotation with the output shaft  54 . When the clutch  53  is engaged, the input shaft  51  and the output shaft  54  are connected for rotation together. When the clutch  51  is disengaged, the input shaft  51  and the output shaft  54  are not connected for rotation together. 
         [0028]    The output shaft  54  is connected for rotation with an electric generator/motor  55  that, in turn, is electrically connected to an electric energy storage device  56 . The electric generator/motor  55  is conventional in the art and is responsive to rotational power supplied from the output shaft  54  for generating electrical power to the electric energy storage device  56 . The electric energy storage device  56  is also conventional in the art and may be embodied as any desired device that can store electrical energy, such as a battery or a capacitor. The electric generator/motor  55  is also responsive to electrical power supplied from the electric energy storage device  56  for rotatably driving the output shaft  54 . The purpose for and manner of operation of the electric generator/motor  55  and the electric energy storage device  56  will be explained below. 
         [0029]    The output shaft  54  is also connected for rotation with a hydraulic pump/motor  57  that, in turn, is electrically connected to a hydraulic energy storage device  58 . The hydraulic pump/motor  57  is conventional in the art and is responsive to rotational power supplied from the output shaft  54  for generating hydraulic power to the hydraulic energy storage device  58 . The hydraulic energy storage device  58  is also conventional in the art and may be embodied as any desired device that can store hydraulic energy, such as an accumulator. The hydraulic generator/motor  57  is also responsive to hydraulic power supplied from the hydraulic energy storage device  58  for rotatably driving the output shaft  54 . The purpose for and manner of operation of the hydraulic generator/motor  57  and the hydraulic energy storage device  58  will also be explained below. 
         [0030]    The electric energy storage device  56  and the hydraulic energy storage device  58  are connected to operate one or more accessories  60  that are adapted for use in conjunction with the drive train system  10 . The electric energy storage device  56  is adapted to operated one or more electrically operated accessories  60 , such as lighting systems, navigation systems, audio systems, and the like. As shown in  FIG. 1 , one or more of the electrically operated accessories  60  may be directly driven from the electric generator/motor  55 . The hydraulic energy storage device  58  is adapted to operated one or more hydraulically operated accessories  60 , such as such as steering systems, braking systems, air conditioning systems, and the like. As also shown in  FIG. 1 , one or more of the hydraulically operated accessories  60  may be directly driven from the hydraulic pump/motor  57 . Lastly, as also shown in  FIG. 1 , the engine  11  may be adapted to operate one or more of accessories  60 . 
         [0031]    The electro-hydraulic machine  50  can be operated in a variety of modes that can improve the performance of the drive train system  10 . Each of the operating modes described below can be accomplished through the use of one or more electrical switches and/or other conventional electrical devices, one or more hydraulic valves and/or other conventional hydraulic devices, and one or more clutches and/or other mechanical devices. The specific arrangement of such electrical, hydraulic, and mechanical devices needed to accomplish each of the operating modes described below is easily within the realm of a person having ordinary skill in the art, and this invention is not intended to be limited to any specific arrangement of same. Additionally, one or more control devices (not shown), such as conventional microprocessors or programmable controllers, may be provided for operating the electro-hydraulic machine  50  in any or all of the various modes. The specific programming and manner of operation of such control devices is also easily within the realm of a person having ordinary skill in the art, and this invention is not intended to be limited to any specific programming or manner of operation of same. 
         [0032]    In a first operating mode, the electro-hydraulic machine  50  can be operated as an electric starter to assist in starting the engine  11  after it has been turned off. To accomplish this, electric energy stored in the electric energy storage device  56  is supplied to the electric generator/motor  55 . In response thereto, the electric generator/motor  55  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be engaged. As a result, rotation of the output shaft  54  of the electro-hydraulic machine  50  causes concurrent rotation of the input shaft  53  of the electro-hydraulic machine  50  and, therefore, the input shaft  22  of the power drive unit  20 . As discussed above, the engine  11  rotatably drives the input shaft  22  of the power drive unit  20 . Thus, when the input shaft  22  of the power drive unit  20 , the engine  11  is rotatably driven in a manner similar to a conventional starter motor (not shown). Thus, in this first operating mode, the electro-hydraulic machine  50  can be operated as an electric starter to assist in starting the engine  11 . 
         [0033]    In a second operating mode, the electro-hydraulic machine  50  can be operated as a hydraulic starter to assist in starting the engine  11  after it has been turned off. To accomplish this, hydraulic energy stored in the hydraulic energy storage device  58  is supplied to the hydraulic pump/motor  57 . In response thereto, the hydraulic pump/motor  57  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be engaged. As a result, rotation of the output shaft  54  of the electro-hydraulic machine  50  causes concurrent rotation of the input shaft  53  of the electro-hydraulic machine  50  and, therefore, the input shaft  22  of the power drive unit  20 . As discussed above, the engine  11  rotatably drives the input shaft  22  of the power drive unit  20 . Thus, when the input shaft  22  of the power drive unit  20 , the engine  11  is rotatably driven in a manner similar to a conventional starter motor (not shown). Thus, in this second operating mode, the electro-hydraulic machine  50  can be operated as a hydraulic starter to assist in starting the engine  11 . 
         [0034]    In a third operating mode, the electro-hydraulic machine  50  can be operated as an electrically-oriented source of either electrical or hydraulic energy to some or all of the accessories  60 . Electrical energy stored in the electric energy storage device  56  can be supplied directly to one or more of the electrically operated accessories  60 , as mentioned above. Additionally, hydraulic energy stored in the hydraulic energy storage device  58  can be supplied directly to one or more of the hydraulically operated accessories  60  by supplying the electrical energy stored in the electric energy storage device  56  to the electric generator/motor  55 . In response thereto, the electric generator/motor  55  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be disengaged. Rotation of the output shaft  54  of the electro-hydraulic machine  50  rotatably drives the hydraulic pump/motor  57 . The hydraulic pump/motor  57  is thus operated as a pump to supply hydraulic energy to one or more of the hydraulically operated accessories  60 . Thus, in this third operating mode, the electro-hydraulic machine  50  can be operated as an electrically-oriented source of either electrical or hydraulic energy to some or all of the accessories  60 . 
         [0035]    In a fourth operating mode, the electro-hydraulic machine  50  can be operated as a hydraulically-oriented source of either electrical or hydraulic energy to some or all of the accessories  60 . Hydraulic energy stored in the hydraulic energy storage device  58  can be supplied directly to one or more of the hydraulically operated accessories  60 , as mentioned above. Additionally, electric energy stored in the electric energy storage device  56  can be supplied directly to one or more of the electrically operated accessories  60  by supplying the hydraulic energy stored in the hydraulic energy storage device  58  to the hydraulic pump/motor  57 . In response thereto, the hydraulic pump/motor  57  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be disengaged. Rotation of the output shaft  54  of the electro-hydraulic machine  50  rotatably drives the electric generator/motor  55 . The electric generator/motor  55  is thus operated as a generator to supply electric energy to one or more of the electrically operated accessories  60 . Thus, in this fourth operating mode, the electro-hydraulic machine  50  can be operated as a hydraulically-oriented source of either electrical or hydraulic energy to some or all of the accessories  60 . 
         [0036]    In a fifth operating mode, the electro-hydraulic machine  50  can be operated as a mechanical alternator to supply electrical energy to one or more of the electrically operated accessories  60  without the use of the electric energy storage device  56 . To accomplish this, the engine  11  is operated while the clutch  53  is engaged. As a result, the output shaft  54  of the electro-hydraulic machine  50  is rotatably driven by the engine  11 . Rotation of the output shaft  54  of the electro-hydraulic machine  50  rotatably drives the electric generator/motor  55 . The electric generator/motor  55  is thus operated as a generator to supply electric energy to one or more of the electrically operated accessories  60 . Thus, in this fifth operating mode, the electro-hydraulic machine  50  can be operated as a mechanical alternator to supply electrical energy to one or more of the electrically operated accessories  60  without the use of the electric energy storage device  56 . 
         [0037]    In a sixth operating mode, the electro-hydraulic machine  50  can be operated as a mechanical pressure pump to supply hydraulic energy to one or more of the hydraulically operated accessories  60  without the use of the hydraulic energy storage device  58 . To accomplish this, the engine  11  is operated while the clutch  53  is engaged. As a result, the output shaft  54  of the electro-hydraulic machine  50  is rotatably driven by the engine  11 . Rotation of the output shaft  54  of the electro-hydraulic machine  50  rotatably drives the hydraulic pump/motor  57 . The hydraulic pump/motor  57  is thus operated as a pump to supply hydraulic energy to one or more of the hydraulically operated accessories  60 . Thus, in this sixth operating mode, the electro-hydraulic machine  50  can be operated as a mechanical pressure pump to supply hydraulic energy to one or more of the hydraulically operated accessories  60  without the use of the hydraulic energy storage device  58 . 
         [0038]    In a seventh operating mode, the electro-hydraulic machine  50  can be operated as an electrically-oriented source of rotational power to supplement the amount of rotational power that is supplied from the engine  11  to the drive train system  10 . To accomplish this, the engine  11  is operated while the clutch  53  is engaged. At the same time, electric energy stored in the electric energy storage device  56  is supplied to the electric generator/motor  55 . In response thereto, the electric generator/motor  55  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be engaged. As a result, supplemental rotational power is supplied from the electro-hydraulic machine  50  to the input shaft  22  of the power drive unit  20 . Thus, in this seventh operating mode, the electro-hydraulic machine  50  can be operated as an electrically-oriented source of rotational power to supplement the amount of rotational power that is supplied from the engine  11  to the drive train system  10 . 
         [0039]    In an eighth operating mode, the electro-hydraulic machine  50  can be operated as a hydraulically-oriented source of rotational power to supplement the amount of rotational power that is supplied from the engine  11  to the drive train system  10 . To accomplish this, the engine  11  is operated while the clutch  53  is engaged. At the same time, hydraulic energy stored in the hydraulic energy storage device  58  is supplied to the hydraulic pump/motor  57 . In response thereto, the hydraulic pump/motor  57  is operated as a motor to rotate the output shaft  54  of the electro-hydraulic machine  50 . At the same time, the clutch  53  is caused to be engaged. As a result, supplemental rotational power is supplied from the electro-hydraulic machine  50  to the input shaft  22  of the power drive unit  20 . Thus, in this eighth operating mode, the electro-hydraulic machine  50  can be operated as a hydraulically-oriented source of rotational power to supplement the amount of rotational power that is supplied from the engine  11  to the drive train system  10 . 
         [0040]    In a ninth operating mode, the electro-hydraulic machine  50  can be operated as either an electrically-oriented torsional damper or a hydraulically-oriented torsional damper for the engine  11 . To accomplish this, supplemental rotational power is supplied from the electro-hydraulic machine  50  to the engine  11  of the drive train system  10  as described above in connection with the seventh or eighth operating modes. However, the application of such supplemental rotational power selected to be similar in magnitude and opposite in phase from any torque ripple that is generated in the input shaft  22  of the power drive unit  20  by the engine  11 . The detection and measurement of the magnitude and phase of such torque ripple can be made in any conventional manner, and the various components of the electro-hydraulic machine  50  (including the clutch  53 , the electric generator/motor  55 , and the hydraulic pump/motor  57 ) can be operated to achieve the desired reduction or cancelation of the torque ripple that is generated in the input shaft  22  of the power drive unit  20  by the engine  11 . Thus, in this ninth operating mode, the electro-hydraulic machine  50  can be operated as either an electrically-oriented torsional damper or a hydraulically-oriented torsional damper for the engine  11 . 
         [0041]    In a tenth operating mode, the electro-hydraulic machine  50  can be operated as either an electrically-oriented brake or a hydraulically-oriented brake to selectively retard the rotation of the input shaft  22  of the power drive unit  20 . To accomplish this, the clutch  53  is caused to be engaged when it is desired to retard the rotation of the input shaft  22  of the power drive unit  20 . When the clutch  53  is engaged, the input shaft  22  of the power drive unit  20  rotatably drives the output shaft  54  of the electro-hydraulic machine  50 . As a result, both the electric generator/motor  55  and the hydraulic pump/motor  57  are rotatably driven. The loads imposed by the electric generator/motor  55  and the hydraulic pump/motor  57  retard the rotation of the output shaft  54  of the electro-hydraulic machine  50  and, therefore, the input shaft  22  of the power drive unit  20 . At the same time, the electric generator/motor  55  is operated as a generator to supply electrical energy to the electric energy storage device  56 , and the hydraulic pump/motor  57  is operated as a pump to supply hydraulic energy to the hydraulic energy storage device  58 . Thus, in this tenth operating mode, the electro-hydraulic machine  50  can be operated as either an electrically-oriented engine brake or a hydraulically-oriented engine brake to selectively retard the rotation of the input shaft  22  of the power drive unit  20 . 
         [0042]    The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.