Abstract:
A multimode clutch may be adapted for selectively connecting and disconnecting front and/or rear axles from respective internal combustion engine and electric motor powertrains connected to such front and rear driving axles in a through-the-road hybrid vehicle. For example, the engine may be part of a front axle driven powertrain connected to the front wheels, while the motor may be part of a separate rear axle driven powertrain connected to the rear wheels, or vice versa. By selective disconnection of an axle not being actively driven, a real time reduction in parasitic losses may be achieved, leading to higher overall operating efficiencies. The multimode clutch offers greater flexibility over the use of standard friction clutches; each multimode clutch may provide four distinct operational modes for accommodating a wide diversity of driving conditions. For example, bi-rotational freewheeling of the rear axle may occur whenever the motor is not in use.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a 35 USC §371 national phase application claiming priority to U.S. Provisional Application Ser. No. 62/040,701 filed on Aug. 22, 2014. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to through-the-road hybrid vehicles having a combustion engine driving one axle and an electric motor independently driving a second axle, and in particular to such a hybrid vehicle employing dual power sources, with at least one multimode mechanical clutch adapted to disconnect at least one of the two axles from its respective power source. 
       BACKGROUND 
       [0003]    Hybrid vehicles are typically powered by the combination of a combustion engine and an electric motor. In a “through-the-road” hybrid vehicle, at least two axles are separately driven; the combustion engine is configured to power one axle, while the electric motor is configured to separately and independently power the second axle. 
         [0004]      FIG. 1  is a schematic illustration of an exemplary “through-the-road” hybrid vehicle  10 , as already known in the art. The vehicle  10  includes a first axle  12 , adapted to drive a first pair of wheels  14 ,  16  through a first differential  18 . The vehicle  10  includes a second axle  20 , adapted to drive a second pair of wheels  22 ,  24  through a second differential  26 . Although the first pair of wheels  14 ,  16  as depicted herein may be front wheels, and the second pair of wheels  22 ,  24  may be rear wheels, either pair of wheels, depending on the nature of a given vehicle  10 , may constitute front wheels or rear wheels of the vehicle  10 . 
         [0005]    The vehicle  10  includes a front axle powertrain  28 , including an internal combustion engine  30  coupled with a transmission (or gearbox)  32  through a friction clutch  34 . For this purpose the transmission  32  includes an input (not shown) adapted to engage and disengage with the friction clutch  34  at an end of the transmission nearest the engine  30 . Internal gearing and an output shaft (neither shown) of the transmission  32  transmit engine torque via the friction clutch  34  from the engine  30  to the first differential  18  by a drive shaft (not shown). In the through-the-road embodiment described herein, the powertrain  28  is configured to only power the first axle  12  and its associated components, including the first differential  18 . 
         [0006]    As is typical, in the through-the-road vehicle  10  the second, or rear, axle  20  is, unlike the first axle  12 , separately and independently powered by an electric motor  40 . As such, the electric motor  40  drives the rear wheels  22 ,  24  through an optional gearbox  42  (to provide, for example, a two-speed gear ratio capability) having an output shaft (not shown) coupled to the second differential  26 . Alternatively, the electric motor  40  may have an output shaft coupled directly to the second differential  26  for providing a single speed drive configuration. Irrespective of whether the rear axle is a single or two speed, the electric motor  40 , including the second differential  26 , and other components configured to drive the second axle  20  may be referred to herein as the rear axle powertrain  44 . 
         [0007]    Adjunctive to the rear axle powertrain  44  is an inverter  50  configured for selectively providing regenerative power to a rechargeable battery  52  adapted to power the electric motor. 
         [0008]    The components of the described hybrid vehicle  10  may be operated and/or controlled in accordance with driving conditions to optimize efficient utilization of the front and rear axle powertrains  28 ,  44 ; i.e., the internal combustion engine  30  and the electric motor  40 , respectively, in different ways. For example, during a combination of stop and go and/or slower driving in urban areas, the rear electric motor-driven powertrain  44  may be utilized more than the front internal combustion engine powertrain  28  to the extent that the powertrain  44  may offer most efficient power while saving fuel. However, during highway driving with less stop and go and at higher speeds, higher utilization of the power train  28  may prove most efficient, for reasons those skilled in the art may best appreciate. 
         [0009]    During use of internal combustion engine powertrain  28 , the friction clutch  34  is engaged and disengaged to selectively connect and disconnect the internal combustion engine  30  to the transmission  32  so that power from the engine  30  is delivered to the front axle  12 . At the same time the front axle  12  is driven, the electric motor  40  may be controlled to provide additional power boosts to the rear axle  20 , or to alternatively use the power supplied by the internal combustion engine  30  to recharge the battery  52 . Conversely, during urban driving situations, the friction clutch  34  may be opened to disconnect the engine  30  from driving the front axle  12 , and power from the battery  48  may be used by the motor  40  to drive the vehicle  10  via the rear axle  20 . During the latter driving condition, the engine  30  may be completely stopped, and/or the friction clutch  34  opened, or disengaged, to conserve fuel. However, during a momentary acceleration of the vehicle  10 , the friction clutch  34  may be re-engaged to provide more responsive acceleration, thus utilizing power from both the engine  30  and the motor  40 . In another variation, the friction clutch  34  may be opened or disengaged to disconnect the engine  30  during deceleration so that the motor  40  may more efficiently recharge the battery  48 ; i.e. without power losses due to engine friction. 
         [0010]    Under presently known arrangements of the friction clutch  34  in the through-the-road hybrid vehicle  10 , the friction clutch  34  in its engaged or closed position is configured to lock the front axle powertrain  28  for rotation of the front axle in either direction. In the disengaged or open position of the friction clutch  34 , the front axle  12  is free to rotate in either direction. This arrangement may create inefficiencies in operation of the hybrid vehicle  10 . Whenever the friction clutch  34  is engaged for driving the vehicle  10  under the power of the engine  30 , or while the vehicle  10  is accelerating under the combined power of the engine  30  and the electric motor  40 , any slowing the engine  30  may cause rotating losses as the front axle powertrain  28  slows, unless the friction clutch  34  is actuated to open to disconnect the engine  30  from the transmission  32 . 
         [0011]    If the friction clutch  34  remains closed, engine rotating losses will be incurred. The latter may be desirable for such vehicles  10  in situations where engine braking is desirable. In most hybrid vehicles, however, regenerative battery power braking is preferred instead, so as to most effectively re-energize the rechargeable battery  52  through the inverter  50 . If the friction clutch  34  is actuated to disconnect the engine  30 , the engine rotating losses may be avoided, but open friction clutch rotating losses remain, as the relatively large surface areas of the facing clutch plates are subjected to oil shear with resulting viscous drag. 
         [0012]    In addition, since the friction clutch  34  must be reclosed whenever the engine  30  is called upon to provide power to the driven wheels  14 ,  16 , the options of leaving the friction clutch  34  closed, may negate efficiencies sought to be achieved by the hybrid vehicle  10 . As such, opening and closing the friction clutch  34 , may effectively negate the efficiencies sought to be achieved, due to the viscous drag and corresponding open clutch rotating losses, as well as increases in duty cycle required for actuating the friction clutch  34 . Therefore, a need exists for an improved strategy for switching between the power sources of a through-the-road hybrid vehicle that can increase energy efficiencies without increasing rotating losses. 
       SUMMARY OF THE DISCLOSURE 
       [0013]    In accordance with one aspect of the present disclosure, a hybrid vehicle includes first and second axles, each axle having a driven wheel at each end thereof. An internal combustion engine driven powertrain is selectively operatively connected to the first axle, and an electric motor driven powertrain is independently and selectively operatively connected to the second axle. A multimode clutch is configured to operatively interconnect at least one of (a) the engine driven powertrain and the first axle, and (b) the motor driven powertrain and the second axle. 
         [0014]    In accordance with another aspect of the present disclosure, the hybrid vehicle further includes the multimode clutch having a first mode allowing the first axle and the engine driven powertrain to rotate independently of each other in both directions of rotation, and a second mode wherein the multimode clutch operatively couples the first axle to the engine driven powertrain so that the first axle and engine driven powertrain rotate together in one direction and rotate independently of each other in an opposite direction. 
         [0015]    In accordance with yet another aspect of the present disclosure, the hybrid vehicle further includes a third mode of the multimode clutch wherein the multimode clutch operatively couples the first axle to the engine driven powertrain so that the first axle and the engine driven powertrain rotate together in both directions of rotation. 
         [0016]    In accordance with a still further aspect of the present disclosure, the hybrid vehicle further includes a controller operatively connected to the electric motor driven powertrain, the controller being configured to transmit control signals to the electric motor and to the internal combustion engine to control speed of the electric motor relative to that of the internal combustion engine as a combined function of vehicle speed and electric motor speed during transitions between front and rear powertrains. 
         [0017]    In accordance with yet another aspect of the present disclosure, the multimode clutch of the hybrid vehicle includes a first race defining an axis, wherein one of the engine and motor driven powertrains and the first and second axles is operatively connected to the first race for rotation therewith, a second race radially disposed about the same axis, and extending circumferentially about the axis, wherein the other one of the powertrains and the axles is operatively connected to the second race for rotation therewith, opposed pairs of pawls operatively connected to the first race and being movable relative to the first race, and an actuator cam adapted for movement relative to the second race. 
         [0018]    In accordance with yet another aspect of the present disclosure, the hybrid vehicle further includes a first selectable actuator cam position corresponding to a first mode of the multimode clutch, the actuator cam engaging the pairs of opposed pawls to prevent the pawls from engaging the second race and to permit the first race to rotate in both a first rotational direction and a second rotational direction independently of the second race. 
         [0019]    In accordance with yet another aspect of the present disclosure, the hybrid vehicle further includes a second selectable actuator cam position corresponding to a second mode of the multimode clutch, wherein rotation of the first race in a first rotational direction causes a first of the pairs of opposed pawls to engage the second race and to thereby lock the first race and the second race together for rotation in the first rotational direction, and wherein rotation of the first race in the second rotational direction causes a second of the pairs of opposed pawls to engage the second race and thereby lock the first race and the second race together for rotation in the second rotational direction. 
         [0020]    Additional aspects are defined by the claims of this patent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a schematic illustration of a presently known through-the-road hybrid vehicle of the type having a friction clutch connecting an internal combustion engine to a transmission; 
           [0022]      FIG. 2  is a schematic illustration of a through-the-road hybrid vehicle incorporating multimode clutches in accordance with the present disclosure; 
           [0023]      FIG. 3  is both a perspective and a cross-sectional view of a portion of one possible embodiment of a multimode clutch schematically depicted in the through-the-road hybrid vehicle of  FIG. 2 ; 
           [0024]      FIG. 4  is an enlarged side view of a portion of one possible embodiment of the multimode clutch of  FIG. 3  with the near inner race plate removed to reveal the internal components, and with an actuator cam in a one-way locked, one-way unlocked position; 
           [0025]      FIG. 5  is a view of the same portion of  FIG. 4 , but with the actuator cam shown in a two-way unlocked position; 
           [0026]      FIG. 6  is a view of the same portion of  FIGS. 4 and 5 , but with the actuator cam shown in a two-way locked position; 
           [0027]      FIG. 7  is a first chart detailing various front axle powertrain operating configurations; 
           [0028]      FIG. 8  is a second chart detailing various rear axle powertrain operating configurations; and 
           [0029]      FIG. 9  is a flowchart depicting an exemplary electronic control unit and associated components that may be utilized in the through-the-road hybrid vehicle of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Although the following description addresses numerous embodiments, each embodiment herein is intended to be exemplary only. Numerous alternative embodiments not set forth herein may be implemented in accordance with the disclosure as well, and they also may fall within the scope of the appended claims the define scope of protection. Moreover, the terms recited in the claims are not intended to be limiting, for example, by implication or otherwise, to have a single particular meaning. 
         [0031]    Making reference now to  FIG. 2 , a schematic illustration of an embodiment of a through-the-road hybrid vehicle  110  constructed in accordance with the present disclosure includes a first axle  112  adapted to drive a pair of driven front wheels  114 ,  116  through a first differential  118 . The vehicle  110  includes a second axle  120  adapted to drive a second pair of wheels  122 ,  124  through a second differential  126 . Although the first pair of wheels  114 ,  116  as depicted may be front wheels, and the second pair of wheels  122 ,  124  may be rear wheels, either pair of wheels, depending on the nature of a given vehicle  110 , may constitute front wheels or rear wheels of the vehicle  110 . 
         [0032]    The vehicle  110  includes a front axle powertrain  128  adapted to drive the front axle  112 . The powertrain  128  includes an internal combustion engine  130  coupled with a transmission (or gearbox)  132 , driven by the engine through a torque converter  134 . A multimode clutch  136  is interposed between the transmission  132  and the differential  118 . The multimode clutch  136  and its operation are discussed in detail below. In the configuration shown, engine torque is transmitted from the engine  130 , through the torque converter  134 , and ultimately through the first axle  112  via the first differential  118 . In the through-the-road embodiment described herein, the powertrain  128  is configured to power only the first axle  112  and its associated components, including the first differential  118 . 
         [0033]    The through-the-road hybrid vehicle  110  incorporates a second axle  120  that is separately and independently powered by an electric motor  140 . As configured, the electric motor  140  selectively drives the rear wheels  122 ,  124  through an optional gearbox  142  having an output shaft (not shown) coupled to the second differential  126 . Alternatively, the electric motor  140  may have an output shaft coupled directly to the second differential  126  for providing a single speed drive configuration. Irrespective of whether the rear axle is a single or two speed, the electric motor  140 , including the second differential  126 , and other components configured to drive the second axle  120  are referred to herein as the rear axle powertrain  144 . 
         [0034]    Interposed between the gearbox  142  and a differential  126  is a second multimode clutch  138  that operates similar to the multimode clutch  136  of the front axle powertrain  128 . An inverter and rechargeable battery (neither shown in  FIG. 2 ) are also associated with the rear axle powertrain  144 , and have functions similar to those already described with respect to  FIG. 1 , including transfer of electrical power between the electric motor  140  and the rechargeable battery. 
         [0035]    Referring now to  FIG. 3 , front and rear multimode clutches  136 ,  138  of the through-the-road hybrid vehicle  110  of  FIG. 2  may be utilized in lieu of the friction-style clutch  34  typically used in the through-the-road hybrid vehicle  10 . In fact, those skilled in the art will appreciate that, with upon incorporation of the multimode clutch  136 ,  138 , the clutch  34  can be replaced by the simple torque converter  134  shown in  FIG. 2 . 
         [0036]    The multimode clutch  136 ,  138  may be of the type illustrated and described in U.S. Prov. Appl. Ser. No. 61/758,356 filed on Jan. 30, 2013 by Papania, entitled “Multi-Mode Clutch Module,” which is expressly incorporated by reference herein. 
         [0037]    The multimode clutch  136  may be identical to, and work similarly to, the multimode clutch  138 . Thus, for the sake of brevity, the multimode clutch  136 ,  138  will only be described with respect to the front axle in the illustrated embodiment. Those skilled in the art will appreciate that the multimode clutch  136 ,  138  may incorporate an interior driven hub  150  that may be operatively connected to an output shaft (not shown) of the internal combustion engine  130  for rotation therewith, and an outer housing  152  that may be operatively connected to a transmission shaft (not show) for rotation therewith. Those skilled in the art will understand that, alternatively, the driven hub  150  may be operatively connected to the transmission shaft, and the outer housing  152  may be connected to the output shaft. The driven hub  150  may contain an array of circumferentially spaced cogs  154  adapted to secure a first, inner, race  156  to the driven hub  150  for rotation therewith. As disclosed, the inner race  156  is physically comprised of first and second spaced inner race plates  156 A,  156 B. A second, outer, race  158  sandwiched between the pair of inner race plates  156 A,  156 B, is situated to allow for relative rotation between the inner race  156  and the outer race  158 , and with the outer race  158  being operatively coupled to the outer housing  152  for rotation therewith. 
         [0038]    In the present design of the multimode clutch  136 ,  138 , an actuator cam  160  is interposed between one of the inner race plates  156 A,  156 B and the outer race  158  for rotation over a predetermined angle about a common axis of the driven hub  150  and the outer housing  152  to control movements of pairs of opposed pawls  162 ,  164  as will be described further hereinafter. The sets of pawls  162 ,  164  are trapped, and hence retained, between the inner race plates  156 A,  156 B to allow limited angular movements of the pawls  162 ,  164  held within bowtie-shaped apertures  166 ,  168 , respectively, subject to the control of the actuator cam  160 . In each set, the combined pawl  162  and corresponding aperture  166  is similar to but oppositely oriented to the combined pawl  164  and corresponding aperture  168 . The elements of the multimode clutch  136 ,  138  are contained within the outer housing  152 . A plurality of spaced apertures  170  are adapted to accommodate rivets (not shown) for providing fixed and rigid securement of each of the inner race plates  156 A and  156 B relative to the other. 
         [0039]    The components of the multimode clutch  136 ,  138  are depicted in  FIGS. 4-6  to illustrate various operational modes of the multimode clutch  136 ,  138  for controlling the relative rotation between the output shaft of the engine  130  and the transmission shaft. Referring first to  FIG. 4 , the outer race  158  is configured to accommodate interactions with the pawls  162 ,  164  by providing the inner circumference of the outer race  158  with circumferentially spaced notches  172 , each defined by and positioned between pairs of radially inwardly projecting cogs  174 . The notches  172  and cogs  174  are configured so that, in the absence of the actuator cam  160 , a toe end  176  of each pawl  162  enters one of the notches  172  and is engaged by the corresponding cog  174  when the driven hub  150  and the inner race  156  rotate in a clockwise direction as viewed in  FIG. 4  relative to the outer housing  152  and the outer race  158  to cause the output shaft  122  and transmission shaft  128  to rotate together. Similarly, a toe end  178  of each pawl  164  enters one of the notches  172  and is engaged by the corresponding cog  174  when the driven hub  150  and the inner race  156  rotate in a counterclockwise direction relative to the outer housing  152  and the outer race  158  to cause the output shaft  122  and transmission shaft  128  to rotate together. 
         [0040]    Within its interior periphery, the actuator cam  160  incorporates a strategically situated array of circumferentially spaced recesses, herein called slots  180 , defined by and situated between projections, herein called cam teeth  182 . The slots  180  and cam teeth  182  are adapted to interact with the pawls  162 ,  164  to control their movement within the apertures  166 ,  168 , respectively, and disposition within the notches  172  and engagement by the cogs  174  as will be described. The actuator cam  160  may further include an actuator tab  184  or other appropriate member or surface that may be engaged by a multimode clutch actuator (shown only schematically in  FIG. 9 ) that is capable of causing the actuator cam  160  to move through its rotational range to the positions shown in  FIGS. 4-6 . The actuator device may be any appropriate actuation mechanism capable of moving the actuator cam  160 , such as a hydraulic actuator such as that shown in the Papania reference cited above, a solenoid actuator, a pneumatic actuator or other appropriate device operatively coupled to the actuator cam and capable of rotating the actuator cam  160  to multiple positions. In the illustrated embodiment, the actuator tab  184  may be disposed within a slot  186  through the outer race and the rotation of the actuator cam  160  may be limited by a first limit surface  188  engaging the actuator tab  184  at the position shown in  FIG. 4  and a second limit surface  190  engaging the actuator tab  184  at the position shown in  FIG. 6 . 
         [0041]    The pawls  162 ,  164  are asymmetrically shaped, and reversely identical. Each of the opposed pawls  162 ,  164  is movably retained within its own bowtie-shaped pawl aperture  166 ,  168 , respectively, of the inner race plates  156 A and  156 B. The toe end  176 ,  178  of each individual pawl  162 ,  164 , respectively, is urged radially outwardly via a spring  192 . Each spring  192  has a base  194 , and a pair of spring arms  196  and  198 . The spring arms  196  bear against the bottoms of the pawls  162 , while the spring arms  198  bear against the bottoms of the pawls  164 , each to urge respective toe ends  176 ,  178  into engagement with the cogs  174  of the outer race  158  when not obstructed by the cam teeth  182  of the actuator cam  160 . It will be appreciated from  FIG. 4  that axially extending rivets  199  are used to secure the inner race plates  156 A,  156 B together. The rivets  199  extend through the apertures  170  in each of the inner race plates  156 A,  156 B to hold the inner race plates  156 A,  156 B rigidly together, and to thus assure against any relative rotation with respect to the inner race plates  156 A,  156 B. In lieu of the rivets  199 , other structural fasteners may be employed within the scope of this disclosure to secure the inner race plates  156 A,  156 B. 
         [0042]    It will be appreciated that the actuator mechanism ultimately controls the actuator tab  184  which, in turn, moves the actuator cam  160  between multiple distinct angular positions. Thus, the positioning of the pawls  162 ,  164  as axially retained between the riveted inner race plates  156 A,  156 B is directly controlled by the actuator cam  160  against forces of springs  192 . In  FIG. 4 , the actuator tab  184  is shown positioned by the actuator mechanism in a first, angularly rightward selectable position, representative of a first, one-way locked, one-way unlocked or open mode. In this position, the slots  180  and cam teeth  182  of the actuator cam  24  are positioned so that the toe ends  176  of the pawls  162  are blocked by cam teeth  182  from engagement with notches  172 , and hence with the cogs  174  on the interior of the outer race  158 . As such, the inner race  156  is enabled to freewheel relative to the outer race  158 , and to thus provide for an overrunning condition when the inner race  156  and the driven hub  150  are rotating clockwise relative to the outer race  158  and the outer housing  152 . Conversely, however, the position of the actuator cam  160  allows of the toe ends  178  of the pawls  164  to enter the slots  180  of the actuator cam  24  due to the biasing force of the spring arms  198 , and to thereby directly engage the cogs  174  of the outer race  158  to lock the inner race  156  and the outer race  158  together whenever the inner race  156  and the driven hub  150  undergo a driving, or counterclockwise rotational movement, thereby causing the driven hub  150  and the outer housing  152  to rotate together. 
         [0043]      FIG. 5  illustrates the actuator tab  184  placed by the actuator mechanism in a second, intermediate selectable position, representative of a two-way unlocked or open mode of the multimode clutch  136 ,  138 . In this position, the slots  180  and the cam teeth  182  of the actuator cam  160  are positioned to prevent the toe ends  176 ,  178  of both pawls  162 ,  164  from entering the slots  180  of the actuator cam  160 , and to maintain disengagement from the cogs  174  of the outer race  158 . With the pawls  162 ,  164  blocked from engagement with the cogs  174 , the inner race  156  and the driven hub  150  are enabled to freewheel relative to the outer race  158  and the outer housing  152  during relative rotation in either the clockwise or the counterclockwise direction. 
         [0044]    In  FIG. 6 , the actuator tab  184  is shown in a third, angularly leftward selectable position, representative of a two-way locked mode of the multimode clutch  136 ,  138 . In this configuration, the actuator cam  160  is positioned so that the toe ends  176 ,  178  of both pawls  162 ,  164  enter the slots  180  of the actuator cam  160  under the biasing forces of the spring arms  196 ,  198 , respectively, and are engaged by the cogs  174  of the outer race  158  as described above to lock the inner race  156  and the driven hub  150  to the outer race  158  and the outer housing  152  for rotation therewith, irrespective of the rotational direction of the inner race  156  and the driven hub  150 . Even though one specific embodiment of the multimode clutch  136 ,  138  is illustrated and described herein, those skilled in the art will understand that alternative configurations of multimode clutches are possible that provide operational modes or positions in addition to two-way locked and two-way unlocked modes, including one-way lock, one-way unlocked modes, and the implementation of such alternative multimode clutches in through-the-road hybrid vehicles  110  in accordance with the present disclosure is contemplated by the inventors. 
         [0045]    The configuration of the multimode clutch  136 ,  138  illustrated and described herein is exemplary, and those skilled in the art will understand that alternative configurations of the multimode clutch  136 ,  138  may be implemented in vehicles  110  and are contemplated by the inventors. For example, depending on the operating requirements for the vehicle  110 , various combinations of the illustrated modes of  FIGS. 4-6  may be implemented by changing the configurations of the actuator cam  160  and/or the notches  172  and cogs  174  of the outer race  158 . The vehicle requirements may not require both the one-way locked, one-way unlocked mode of  FIG. 4  and the two-way locked mode of  FIG. 6 . In such cases, the cam teeth  182  and actuator tabs  184  may be reconfigured to place the multimode clutch ( 124 ) in the two-way unlocked mode of  FIG. 5  and the required one of the modes of  FIGS. 4 and 6 . Moreover, it may be necessary or desired to provide separate one-way locked, one-way unlocked modes for both directions of rotation so that in one mode the pawls  162  engage the outer race  158  when the inner race  156  rotates clockwise as viewed in the drawing figures, and in another mode the pawls  164  engage the outer race  158  when the inner race  156  rotates counterclockwise. 
         [0046]    Additionally, the relationships between the inner race  156 , the outer race  158  and the pawls  162 ,  164  may be varied as necessary to alternatively lock and unlock the inner race  156  and the outer race  158 . For example, the apertures  166 ,  168  and, correspondingly the pawls  162 ,  164 , may be positioned on the outer race  158 , and the inner race  156  may be provided with corresponding structures for engaging the pawls  162 ,  164  when necessary to lock the inner race  156  and the outer race  158 . Moreover, it is contemplated that the pawls  162 ,  164  may be capable of moving through alternative paths of motion into and out of engagement with their corresponding locking structures, with the actuator cam  160  and a multimode clutch actuator  135  configured to move the pawls  162 ,  164  along the required paths of motion. For example, the pawls  162 ,  164  could move radially or axially between locked positions and unlocked positions instead of through rotation as shown in the illustrated embodiments. 
         [0047]    It is also contemplated that other multimode clutches may be implemented in the through-the-road hybrid vehicle  110  as alternatives to the multimode clutch  136 ,  138  illustrated and described herein and that may be capable of operating to couple and uncouple the output shaft and transmission shaft as necessary to implement a power control strategy for the vehicle  110 . Examples of alternative clutches may be found in U.S. Pat. No. 6,062,361 issued on May 16, 2000 to Showalter, entitled “Acceleration Sensitive Double Overrunning Clutch,” U.S. Pat. No. 6,092,634 issued on Jul. 25, 2000 to Kremer et al., entitled “Compliant Cage for a Roller-Type Bi-Directional One-Way Clutch Mechanism,” U.S. Pat. No. 6,290,044 issued on Sep. 18, 2001 to Burgman et al., entitled “Selectable One-Way Clutch Assembly,” U.S. Pat. No. 6,745,880 issued on Jun. 8, 2004 to Yuergens, entitled “Two-Way Clutch Assembly having Selective Actuation,” U.S. Pat. No. 6,832,674 issued on Dec. 21, 2004 to Blair et al., entitled “Bi-Directional Four-Mode Clutch,” U.S. Pat. No. 6,814,201 issued on Nov. 9, 2004 to Thomas, entitled “Bi-Directional Axially Applied Pawl Clutch Assembly,” and U.S. Pat. No. 8,051,959 issued on Nov. 8, 2011 to Eisengruber, entitled “Controllable or Selectable Bi-Directional Overrunning Coupling Assembly,” each of which is expressly incorporated by reference herein. 
         [0048]    Additional alternative ratchet, spring, roller and ball, and sprag-type clutches configured to be controlled to operate in multiple coupling modes are also contemplated by the inventors as having use in through-the-road hybrid vehicles  110  in accordance with the present disclosure to control the coupling of the output shaft and the transmission shaft and implement a power distribution strategy for the internal combustion engine  130  and the electric motor  140  of the vehicle  110 . For such alternative clutches, it is contemplated by the inventors that those skilled in art will be able to operatively couple the clutches between respective output and transmission shafts in the manner disclosed herein, and to operatively connect mode-switching actuation mechanisms of the clutches to control elements as described hereinafter to control the actuation mechanisms for transitioning between available operating modes of the clutches, and to control the power transmission in the vehicle  110  as discussed below. 
         [0049]    In the embodiment of the vehicle  110  depicted in  FIG. 2 , the use of two multimode clutches  136 ,  138  is contemplated. The first multimode clutch  136  is employed as part of the first or front powertrain  128 , and the second multimode clutch  138  is employed in the second or rear powertrain  144 . Alternatively, this disclosure encompasses use of only one multimode clutch in the vehicle  110  as, for example, the use of a single front multimode clutch  136  in the first powertrain  128 , while utilizing a simple friction or dog clutch, in lieu of the multimode clutch  138 , in the rear powertrain  144 . Conversely, a single rear multimode clutch  138  could be used in the second or rear powertrain  144 , in concert with a simple friction or dog clutch, in lieu of the multimode clutch  136 , in the front powertrain  128 . While perhaps not necessarily ideal, the use of at least one multimode clutch in accordance with either of the above alternately described configurations could provide at least some efficiency improvements by reducing some of the system parasitic drag. 
         [0050]    Referring now to  FIG. 7 , an operating chart outlines various configurations of the above-described multimode clutch  136  incorporated into the front axle powertrain  128 . As disclosed, the multimode clutch  136  may be situated internal to the housing (not shown) of the transmission  132 , physically juxtaposed between the gearbox (not shown) and the first differential  118 . Such configuration would permit control of the multimode clutch via an electromagnetic actuation system or via an electro hydraulic actuation system. If electro hydraulically, transmission fluid may be utilized as a control oil source. 
         [0051]    In accordance with the chart of  FIG. 7 , the multimode clutch  136  (referenced in the chart as an “MMCM”, an acronym for “multimode clutch module” since the multimode clutches  136 ,  138  of this disclosure may be installed as a component or “module”) may incorporate the following control modes, thus offering greater flexibility than any known prior art configurations:
       1) While the internal combustion engine is propelling the vehicle  110 , the multimode clutch  136  can be locked in both rotational positions of the front axle  112 . This lock/lock configuration ( FIG. 6 ) provides positive engagements for both forward and reverse rotations of the front axle  112 , and is advantageous for utilization of a reverse gear configuration, as well as for flexibility of having engine braking availability (in lieu of providing battery power regeneration) while descending a hill.   2) While the electric motor is propelling the vehicle  110 , the engine may be off, and the multimode clutch  136  may be open in both rotational directions ( FIG. 5 ) of the front axle  112 . This will substantially reduce parasitic losses during operation of the electric motor only.   3) During transition of the engine from on to off, with the electric motor propelling the vehicle  110 , the multimode clutch  136  may be open in both rotational directions ( FIG. 5 ), again substantially reducing parasitic drag.   4) During transition of the engine from off to on, while the electric motor is propelling the vehicle, the multimode clutch  136  may be locked in the driving rotational direction, while open in the non-driving rotational direction ( FIG. 4 ), particularly as a synchronous speed as being achieved. Such a configuration allowing freewheeling in the one direction will allow the engine to endure an overrunning condition, such as might occur while descending a hill. At the same time, being locked in the driving direction allows the engine to increase speed from zero to a synchronous speed target for the transition to engine driving the front axle of the vehicle. Once the engine is driving the vehicle, the multimode clutch  136  is switched to the lock-lock mode of  FIG. 6 .       
 
         [0056]    Referring now to  FIG. 8 , a second operating chart outlines various configurations of the above-described multimode clutch  138 , as may be incorporated into the rear axle powertrain  144 . The multimode clutch  138  is contemplated to be operated electro-mechanically, as no appropriately regulated hydraulic fluid source is normally provided at rear axle locations. 
         [0057]    In accordance with the chart of  FIG. 8 , the multimode clutch  138  may incorporate the following control modes, again offering greater flexibility than any known prior art configurations:
       1) While the electric motor  140  is either propelling the vehicle or regenerating battery power, the multimode clutch  138  can be locked in both rotational directions of the rear axle  120 . A lock in both directions ( FIG. 6 ) permits the electric motor to drive the vehicle or to transmit its energy via the inverter to achieve regenerative braking.   2) While the electric motor  140  is off, with the engine propelling the vehicle, the multimode clutch  138  may be configured to be open in both rotational directions ( FIG. 5 ) to avoid parasitic drag otherwise produced by components of the rear axle powertrain  144 .   3) During transition of the electric motor from on to off, while the engine is beginning to propel the vehicle, the multimode clutch  138  may be configured to be open in both directions ( FIG. 5 ), again to reduce parasitic drag.   4) During transition of the electric motor  140  from off to on, while the engine is propelling the vehicle, the multimode clutch  138  may be configured to be locked in the driving direction, while open in the non-driving direction as the electric motor speed increases from zero to a target synchronous speed.       
 
         [0062]      FIG. 9  illustrates one exemplary configuration of a controller  200  that may be implemented in the through-the-road hybrid vehicle  110  to efficiently control respective front and rear axle operations of the internal combustion engine  130  and the electric motor  140  to provide power to drive the vehicle  110  under various driving and operating conditions. The controller provides an integrated operation of the multimode clutch  136 ,  138  for selectively entering the one-way lock, one-way unlock mode of  FIG. 4 , the two-way unlock mode of  FIG. 5  and the two-way lock mode of  FIG. 6 , in accordance with operating conditions of the vehicle  110 . The controller  200  may include a microprocessor  202  for executing specified programs that control and monitor functions associated with the vehicle  110 , including functions outside the scope of the present disclosure. The microprocessor  202  includes a memory  204 , such as read only memory (ROM)  206 , for storing a program or programs, and a random access memory (RAM)  208  which may serve as a working memory area for use in executing the program(s) stored in the memory  204 . 
         [0063]    Although the microprocessor  202  is shown herein, it is also possible and contemplated to use other electronic components such as a microcontroller, an ASIC (application specific integrated circuit) chip, or any other integrated circuit device. Although a single controller  200  for the vehicle  110  is illustrated and referenced herein, those skilled in the art will understand that the various processing functions described herein may be implemented across multiple control structures. For purposes of the present application, the controller  200  may refer collectively to the performance of the control strategy discussed herein even when implemented across multiple control devices. 
         [0064]    The controller  200  electrically connects to the control elements of the through-the-road hybrid vehicle  110  ( FIG. 2 ), as well as various input devices for commanding the operation of the vehicle  110  and for monitoring its performance. As a result, the controller  200  may be electrically connected to input devices providing control signals to the controller  200  that may include a speed controller  210  for the electric motor  140 , such as a gas pedal or accelerator manipulated by an operator to regulate the speed of the vehicle  110 , an vehicle speed sensor  212  for measuring actual road speed of the vehicle  110 , such as a rotary speed sensor measuring rotational speed of an output shaft. By way of example, as a sub-controller for the rear axle power train that includes the electric motor  140 , a controller  200  may be configured to be electrically connected to output devices to which control signals are transmitted and from which control signals may be received by the controller  200 , such as, for example, the electric motor  140  of the vehicle  110 , the transmission  132 , the engine  130 , and a multimode clutch actuator  135  associated with the rear axle, again by way of example only. 
         [0065]    Those skilled in the art will understand that described input devices, output devices, and operations of the controller  200  provided herein are exemplary only, and that additional and alternative devices may be implemented in through-the-road hybrid vehicles  110  in accordance with the present disclosure to monitor operations of the vehicles  110 , along with inputs provided by operators of the vehicles  110 , and to control the engine  130 , the electric motor  140 , front and rear axle multimode clutches  136 ,  138 , and other systems of the vehicle  110 , to assure desired vehicle performance under a variety of driving conditions. 
       INDUSTRIAL APPLICABILITY 
       [0066]    Integration of the multimode clutch  136 ,  138  within the through-the-road hybrid vehicle  110  may allow for direct replacement of the friction clutch  34  of the hybrid vehicle  10  of  FIG. 1 . The multimode clutch  136 ,  138  can offer at least the three operating modes discussed above, including a one-way lock, one-way unlock mode ( FIG. 4 ) wherein the multimode clutch  136 ,  138  locks in one direction and freewheels in the opposite direction; a two-way unlock mode ( FIG. 5 ) wherein the multimode clutch  136 ,  138  freewheels in both directions; and a two-way lock mode ( FIG. 6 ) wherein the multimode clutch  136 ,  138  is locked in both directions. 
         [0067]    The controller  200  may be configured to cause the multimode clutch  136 ,  138  via the multimode clutch actuator  135  to alternate between the available operating modes based on the desired and/or experienced vehicle operation conditions. The specific strategy for operating the engine  130 , the electric motor  140  and the multimode clutch  136 ,  138  to utilize the power of the engine  130  and/or the electric motor  140  to drive the vehicle  110 , and to selectively engage the available modes of the multimode clutch  136 ,  138  to implement the strategy may vary depending on the operating requirements of the vehicle  110  and decisions made in designing the vehicle  110 . An optimal strategy for maximizing the fuel efficiency of the vehicle  110  may take into account the charted examples provide in  FIGS. 7 and 8 . The examples set forth hereinafter are provided to illustrate various options for utilizing the inherent flexibility provided by the multimode clutch  136 ,  138 . 
         [0068]    As set forth in the foregoing, implementation of the multimode clutch  136 ,  138  in the through-the-road hybrid vehicle  110  as a substitute for the previously known friction clutch  34  may improve the efficiency of the vehicle  110 . As just one example, the multimode clutch  136 ,  138  may improve the system efficiency of the through-the-road hybrid vehicle  110  by reduction of rotating losses, as may be achieved when the multimode clutch  136 ,  138  is in the one-way locked, one-way unlocked position of  FIG. 4  to allow the transmission shaft to freewheel relative to the output shaft whenever the vehicle coasts or decelerates. 
         [0069]    Moreover, although only two operative multimode clutches  136 ,  138  are depicted and described with respect to the vehicle  110 , alternate embodiments may be configured to include at least two multimode clutches on each axle. For example, two of such clutches could be positioned on each of the axles  112  and  120 . In one such configuration, one of a pair of front axle multimode clutches would be situated between each front axle wheel  114 ,  116  and the first differential  118 , while one of a second pair of multimode clutches would be situated between each rear axle wheel  122 ,  124  and the second differential  126 , demonstrating just one example of the potential flexibility of multimode clutch use.