Abstract:
An actuation device having a piston is used to actuate a mechanical or friction clutch by means of differential pressure. Two sides of a piston are pressurized, and the relative pressure between the two sides is decreased or increased to move the piston in either direction. The position of the piston may be determined using position feedback, or with springs of known spring rates, two piston areas, and knowing the pressures of the two areas. The actuation device may be used with a selectable clutch to actuate an actuation cam, and may also have application with other clutches requiring the ability to achieve multiple positions and clutch modes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application claims priority under 35 USC §119(e) to U.S. Provisional Patent Application Ser. No. 62/302,120 filed on Mar. 1, 2016. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to clutches, and in particular to clutches having multiple modes of engagement with a rotating element for selectively locking the element against rotation and allowing the element to rotate freely in one or both directions. 
       BACKGROUND 
       [0003]    An automotive vehicle typically includes an internal combustion engine containing a rotary crankshaft configured to transfer motive power from the engine through a driveshaft to turn the wheels. A transmission is interposed between engine and driveshaft components to selectively control torque and speed ratios between the crankshaft and driveshaft. In a manually operated transmission, a corresponding manually operated clutch may be interposed between the engine and transmission to selectively engage and disengage the crankshaft from the driveshaft to facilitate manual shifting among available transmission gear ratios. 
         [0004]    On the other hand, if the transmission is automatic, the transmission will normally include an internal plurality of automatically actuated clutch units adapted to dynamically shift among variously available gear ratios without requiring driver intervention. Pluralities of such clutch units, also called clutch modules, are incorporated within such transmissions to facilitate the automatic gear ratio changes. 
         [0005]    In an automatic transmission for an automobile, anywhere from three to ten forward gear ratios may be available, not including a reverse gear. The various gears may be structurally comprised of inner gears, intermediate gears such as planet or pinion gears supported by carriers, and outer ring gears. Specific transmission clutches may be associated with specific sets of the selectable gears within the transmission to facilitate the desired ratio changes. 
         [0006]    Because automatic transmissions include pluralities of gear sets to accommodate multiple gear ratios, the reliability of actuators used for automatically switching clutch modules between and/or among various available operating modes is a consistent design concern. It is also desirable to provide smooth transitions between the operating modes when the clutch modules engage and disengage from the gears. These considerations are also important in other operating environments where selectable clutch modules may be implemented to selectively allow and restrict the rotation of rotating components such as gears, shafts, torque converter components and the like. Therefore, much effort has been directed to finding ways to assure actuator reliability and seamless performance at competitive costs. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In one aspect of the present disclosure, an actuator device for a selectable clutch having a plurality of mode positions for controlling relative rotation between two components connected by the selectable clutch is disclosed. The actuator device may include a piston housing having an exterior surface, a piston housing longitudinal bore extending longitudinally there through, a first fluid passage extending inwardly from the exterior surface and intersecting the piston housing longitudinal bore proximate a first bore end, and a second fluid passage extending inwardly from the exterior surface and intersecting the piston housing longitudinal bore proximate a second bore end, and a piston having a piston body disposed within the piston housing longitudinal bore for longitudinal motion therein. A first pressure force acting on the piston body toward the second bore end is equal to a first pressure supplied at the first fluid passage multiplied by a first area equal to a first piston body cross-sectional area of the piston body, and a second pressure force acting on the piston body toward the first bore end is equal to a second pressure supplied at the second fluid passage multiplied by a second area equal to a second piston body cross-sectional area of the piston body. 
         [0008]    In another aspect of the present disclosure, a selectable clutch is disclosed. The selectable clutch may include an outer race, an inner race rotatable relative to the outer race, a selective locking mechanism having a plurality of locking modes for controlling relative rotation between two components connected by the selectable clutch, actuator cam that is rotatable between a plurality of mode positions each causing the selective locking mechanism to engage one of the plurality of locking modes, and an actuator device such as that described in the preceding paragraph operatively connected to the actuator cam to move the selective locking mechanism between the plurality of mode positions as the main piston moves longitudinally within the piston housing longitudinal bore. 
         [0009]    Additional aspects are defined by the claims of this patent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is both a perspective and a cross-sectional view of a portion of one possible embodiment of a selectable in the form of a multimode clutch module that may be implemented in vehicles; 
           [0011]      FIG. 2  is an enlarged side view of a portion of one possible embodiment of the multimode clutch module of  FIG. 1  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; 
           [0012]      FIG. 3  is the enlarge view of one possible embodiment of the multimode clutch module of  FIG. 1  with the actuator cam in a two-way unlocked position; 
           [0013]      FIG. 4  is the enlarge view of the multimode clutch module of  FIG. 1  with the actuator cam in a two-way locked position; 
           [0014]      FIG. 5  is a cross-sectional view taken through line  5 - 5  of  FIG. 2  of an embodiment of an actuator device in accordance with the present disclosure in position to place the actuator cam in the one-way locked, one-way unlocked position; 
           [0015]      FIG. 6  is a cross-sectional view taken through line  6 - 6  of  FIG. 3  of the embodiment of the actuator device in position to place the actuator cam in the two-way unlocked position; 
           [0016]      FIG. 7  is a cross-sectional view taken through line  7 - 7  of  FIG. 4  of the embodiment of the actuator device in position to place the actuator cam in the one-way locked, one-way unlocked position; and 
           [0017]      FIG. 8  is a cross-sectional view taken through line  5 - 5  of  FIG. 2  of an alternative embodiment of an actuator device in accordance with the present disclosure in position to place the actuator cam in the one-way locked, one-way unlocked position; 
           [0018]      FIG. 9  is a cross-sectional view taken through line  6 - 6  of  FIG. 3  of the alternative embodiment of the actuator device in position to place the actuator cam in the two-way unlocked position; and 
           [0019]      FIG. 10  is a cross-sectional view taken through line  7 - 7  of  FIG. 4  of the alternative embodiment of the actuator device in position to place the actuator cam in the one-way locked, one-way unlocked position. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In accordance with the present disclosure, a selectable clutch, such as a multimode clutch module may be implemented at various locations of a vehicle (not shown) to provide multiple modes for connecting and disconnecting rotatable components to prevent or allow, respectively, relative rotation between two components. Referring to  FIG. 1 , a multimode clutch  10  of a vehicle may be of the type illustrated and described in Intl. Publ. No. WO 2014/120595 A1, published on Aug. 7, 2014, by Papania, entitled “Multi-Mode Clutch Module,” which is expressly incorporated by reference herein. While the multimode clutch  10  is illustrated and described herein, those skilled in art will understand that actuator devices in accordance with the present disclosure may be implemented with other types of selectable clutches providing multiple modes for connecting and disconnecting rotatable components to prevent or allow, respectively, relative rotation between two components, and the use of the actuator device with such selectable clutches is contemplated by the inventors. In the illustrated embodiment, the multimode clutch  10  may incorporate an interior driven hub  50  and an outer housing  52  that may be locked for rotation together in some modes of the multimode clutch  10  and may be unlocked for independent rotation with respect to each other in other modes of the multimode clutch  10  as will be described more fully below. The driven hub  50  may contain an array of circumferentially spaced cogs  54  adapted to secure an inner race  56  to the driven hub  50  for rotation therewith. As disclosed, the inner race  56  is comprised of first and second spaced plates  56 A and  56 B. An outer race  58  sandwiched between the pair of inner race plates  56 A,  56 B, is situated so as to allow for relative rotation between inner race  56  and the outer race  58 , and with the outer race  58  being operatively coupled to the outer housing  52  for rotation therewith. 
         [0021]    In the present design of the multimode clutch  10 , an actuator cam  60  is interposed between one of the race plates  56 A,  56 B and the outer race  58  for rotation over a predetermined angle about a common axis of the driven hub  50  and the outer housing  52  to control movements of pairs of opposed pawls  62 ,  64  as will be described further hereinafter. The sets of pawls  62 ,  64  are trapped, and hence retained, between the inner race plates  56 A,  56 B to allow limited angular movements of the pawls  62 ,  64  held within bowtie shaped apertures  66 ,  68 , respectively, subject to the control of the actuator cam  60 . In each set, the combined pawl  62  and corresponding aperture  66  is similar to but oppositely oriented to the combined pawl  64  and corresponding aperture  68 . The elements of the multimode clutch  10  are contained within the outer housing  52 . A plurality of spaced apertures  70  are adapted to accommodate rivets (not shown) for providing fixed and rigid securement of each of the two inner race plates  56 A and  56 B relative to the other. 
         [0022]    The operational components of the multimode clutch  10  are illustrated in  FIGS. 2-4  that illustrate the various operational modes of the multimode clutch  10  for controlling the relative rotation between the components attached to the driven hub  50  and the outer housing  52 . Referring first to  FIG. 2 , the outer race  58  is configured to accommodate interactions with the pawls  62 ,  64  by providing the inner circumference of the outer race  58  with circumferentially spaced notches  72 , each defined by and positioned between pairs of radially inwardly projecting cogs  74 . The notches  72  and cogs  74  are configured so that, in the absence of the actuator cam  60 , a toe end  76  of each pawl  62  enters one of the notches  72  and is engaged by the corresponding cog  74  when the driven hub  50  and the inner race  56  rotate in a clockwise direction as viewed in  FIG. 2  relative to the outer housing  52  and the outer race  58  to cause the connected components to rotate together. Similarly, a toe end  78  of each pawl  64  enters one of the notches  72  and is engaged by the corresponding cog  74  when the driven hub  50  and the inner race  56  rotate in a counterclockwise direction relative to the outer housing  52  and the outer race  58  to cause the connected components to rotate together. 
         [0023]    Within its interior periphery, the actuator cam  60  incorporates a strategically situated array of circumferentially spaced recesses, herein called slots  80 , defined by and situated between projections, herein called cam teeth  82 . The slots  80  and cam teeth  82  are adapted to interact with the pawls  62 ,  64  to control their movement within the apertures  66 ,  68 , respectively, and disposition within the notches  72  and engagement by the cogs  74  as will be described. The actuator cam  60  may further include an actuator tab  84  or other appropriate member or surface that may be engaged by an actuator device  100  that is capable of causing the actuator cam  60  to move through its rotational range to the positions shown in  FIGS. 2-4 . The actuator device  100  may be any appropriate actuation mechanism capable of moving the actuator cam  60 , such as a hydraulic actuator as illustrated and described below operatively coupled to the actuator cam  60  and capable of rotating the actuator cam  60  to multiple positions. The actuator tab  84  may include a radially extending slot  85  that receives a cam actuator bar  102  extending from a longitudinally extending slot  104  of the actuator device  100 . The cam actuator bar  102  may transmit forces from the actuator device  100  to rotate the actuator cam  60  in the clockwise and counterclockwise directions. The interconnection between the actuator cam  60  and the actuator device  100  is illustrative, and alternative arrangements and linkages facilitating conversion of translational motion of the actuator device  100  into rotational motion of the actuator cam  60  to shift between a plurality of available clutch modes are contemplated and will be apparent to those skilled in the art. In the illustrated embodiment, the actuator tab  84  may be disposed within a slot  86  through the outer race and the rotation of the actuator cam  60  may be limited by a first limit surface  88  engaging the actuator tab  84  at the position shown in  FIG. 2  and a second limit surface  90  engaging the actuator tab  84  at the position shown in  FIG. 4 . 
         [0024]    The pawls  62 ,  64  are asymmetrically shaped, and reversely identical. Each of the opposed pawls  62 ,  64  is movably retained within its own bowtie-shaped pawl aperture  66 ,  68 , respectively, of the inner race plates  56 A and  56 B. The toe end  76 ,  78  of each individual pawl  62 ,  64 , respectively, is urged radially outwardly via a spring  92 . Each spring  92  has a base  94 , and a pair of spring arms  96  and  98 . The spring arms  96  bear against the bottoms of the pawls  62 , while the spring arms  98  bear against the bottoms of the pawls  64 , each to urge respective toe ends  76 ,  78  into engagement with the cogs  74  of the outer race  58  when not obstructed by the cam teeth  82  of the actuator cam  60 . It will be appreciated from  FIG. 2  that axially extending rivets  99  are used to secure the inner race plates  56 A,  56 B together. The rivets  99  extend through the apertures  70  in each of the plates  56 A,  56 B to hold the two plates  56 A,  56 B rigidly together, and to thus assure against any relative rotation with respect to the plates  56 A,  56 B. In lieu of the rivets  99 , other structural fasteners may be employed within the scope of this disclosure to secure the inner race plates  56 A,  56 B. 
         [0025]    It will be appreciated that the actuator device  100  ultimately controls the actuator tab  84  which, in turn, moves the actuator cam  60  between multiple distinct angular positions. Thus, the positioning of the pawls  62 ,  64  as axially retained between the riveted inner race plates  56 A,  56 B is directly controlled by the actuator cam  60  against forces of springs  92 . In  FIG. 2 , the actuator tab  84  is shown positioned by the actuator device  100  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  80  and cam teeth  82  of the actuator cam  60  are positioned so that the toe ends  76  of the pawls  62  are blocked by cam teeth  82  from engagement with notches  72 , and hence with the cogs  74  on the interior of the outer race  58 . As such, the inner race  56  is enabled to freewheel relative to the outer race  58 , and to thus provide for an overrunning condition when the inner race  56  and the driven hub  50  are rotating clockwise relative to the outer race  58  and the outer housing  52 . Conversely, however, the position of the actuator cam  60  allows of the toe ends  78  of the pawls  64  to enter the slots  80  of the actuator cam  60  due to the biasing force of the spring arms  98 , and to thereby directly engage the cogs  74  of the outer race  58  to lock the inner race  56  and the outer race  58  together whenever the inner race  56  and the driven hub  50  undergo a driving, or counterclockwise rotational movement, thereby causing the driven hub  50  and the outer housing  52  to rotate together. 
         [0026]      FIG. 3  illustrates the actuator tab  84  placed by the actuator device  100  in a second, intermediate selectable position, representative of a two-way unlocked or open mode of the multimode clutch  10 . In this position, the slots  80  and the cam teeth  82  of the actuator cam  60  are positioned to prevent the toe ends  76 ,  78  of both pawls  62 ,  64  from entering the slots  80  of the actuator cam  60 , and to maintain disengagement from the cogs  74  of the outer race  58 . With the pawls  62 ,  64  blocked from engagement with the cogs  74 , the inner race  56  and the driven hub  50  are enabled to freewheel relative to the outer race  58  and the outer housing  52  during relative rotation in either the clockwise or the counterclockwise direction. 
         [0027]    In  FIG. 4 , the actuator tab  84  is shown in a third, angularly leftward selectable position, representative of a two-way locked mode of the multimode clutch  10 . In this configuration, the actuator cam  60  is positioned so that the toe ends  76 ,  78  of both pawls  62 ,  64 enter the slots  80  of the actuator cam  60  under the biasing forces of the spring arms  96 ,  98 , respectively, and are engaged by the cogs  74  of the outer race  58  as described above to lock the inner race  56  and the driven hub  50  to the outer race  58  and the outer housing  52  for rotation therewith, irrespective of the rotational direction of the inner race  56  and the driven hub  50 . 
         [0028]    Even though one specific embodiment of the multimode clutch  10  is illustrated and described herein, those skilled in the art will understand that alternative configurations of multimode clutches and other selectable clutches are possible that provide operational modes or positions as alternatives or in addition to two-way unlocked and two-way locked modes ( FIGS. 3 and 4 ), and the one-way locked, one-way unlocked mode ( FIG. 2 ). For example, an additional one-way locked, one-way unlocked mode that may provide for an overrunning condition when the inner race  56  and the driven hub  50  are rotating counter clockwise relative to the outer race  58  and the outer housing  52 , and to lock the inner race  56  and the outer race  58  together whenever the inner race  56  and the driven hub  50  undergo a clockwise rotational movement so the driven hub  50  and the outer housing  52  rotate together. Moreover, alternate structures providing some or all of the modes discuss herein for selectable clutches may be implemented in a similar manner in vehicles, such as that illustrated and described in U.S. Pat. No. 8,079,453, published on Dec. 20, 2011, by Kimes, entitled “Controllable Overrunning Coupling Assembly.” The implementation of such alternative selectable clutches in vehicles and controlling the mode switching using such clutches with actuator devices in accordance with the present disclosure would be within the capabilities of those skilled in the art and is contemplated by the inventors. 
         [0029]      FIG. 5  illustrates one embodiment of the actuator device  100  shown in a cross-sectional view taken through line  5 - 5  of  FIG. 2 . The actuator device  100  may include a piston housing  110  having a longitudinal bore  112  extending inwardly into the piston housing  110  from an open end  114  to a closed end  116  disposed opposite the open end  114 . The longitudinal bore  112  may have a generally constant inner diameter as the longitudinal bore  112  extends inwardly to accommodate various internal components of the actuator device  100 . However, the longitudinal bore  112  may include a cap bore portion  118  proximate the open end  114  that transitions to a main bore portion  120  having a constant inner diameter. The longitudinal bore  112  may further define a cap snap ring annular groove  122  in the cap bore portion  118  having a larger inner diameter than the cap bore portion  118 , and a cap engagement surface  124  configured to receive and engage a cap  126  inserted through the open end  114  of the longitudinal bore  112  to retain the internal components within the actuator device  100 . The cap  126  may be held in place by a cap snap ring  128 . The cap snap ring  128  may be annular and have an outer diameter that is greater than the inner diameter of the cap bore portion  118 , and may be pressed into the cap snap ring annular groove  122  to lock the cap  126  in place. 
         [0030]    Additional passages may be defined in the piston housing  110 . The longitudinal slot  104  may extend inwardly from an exterior surface  130  of the piston housing  110  and intersect the longitudinal bore  112  approximately midway between the open end  114  and the closed end  116 . A first fluid passage  132  may extend inwardly from the exterior surface  130  and intersect the main bore portion  120  proximate the open end  114 . A second fluid passage  134  may extend inwardly from the exterior surface  130  and intersect the main bore portion  120  proximate the closed end  116 . The first fluid passage  132  and the second fluid passage  134  may be configured for connection to conduits (not shown) from fluid sources (not shown) of the vehicle for provision hydraulic fluid to opposite ends of the main bore portion  120 . As discussed further below, one or both of the fluid passages  132 ,  134  may be connected to pressurized fluid sources providing hydraulic fluid with varying pressures to control the operation of the actuator device  100  and, correspondingly, the multimode clutch  10 . 
         [0031]    The actuator device  100  may include a piston  140  disposed within the longitudinal bore  112  and slidable back and forth in the longitudinal direction within the longitudinal bore  112 . The piston  140  may include a piston body  142  having a first piston stop  144  and a second piston stop  146  extending outwardly longitudinally from opposite sides of the piston body  142 . The first piston stop  144  may engage the cap  126  and the second piston stop  146  may engage a closed end wall  148  to ensure that the piston body  142  is maintained between the first fluid passage  132  and the second fluid passage  134 . The piston body  142  may have a piston body outer diameter that is less than the inner diameter of the main bore portion  120  so that the piston  140  may slide therein without leakage of hydraulic fluid there between. If necessary, appropriate seals (not shown) may be provided at the interface between the main bore portion  120  and the piston body  142  to further prevent leakage of hydraulic fluid. The cam actuator bar  102  may have an end operatively connected to the piston body  152  and extend outwardly through the longitudinal slot  104  to the exterior of the piston housing  110 . 
         [0032]    A piston spring  150  may be disposed within the main bore portion  120  of the longitudinal bore  112  to provide a biasing force on the piston  140 . In the illustrated embodiment, the piston spring  150  may be compressed between the cap  126  and the piston  140  to provide a force biasing the piston  140  toward the closed open end  116  of the longitudinal bore  112 . Absent other forces acting on the piston  140 , the piston spring  150  will move the piston  140  to the right as shown in  FIGS. 5-7  until the second piston stop  146  is engaged by the closed end wall  148 . With this arrangement, the actuator device  100  may default to the mode position shown in  FIG. 7 . The piston spring  150  may be placed on the opposite side of the piston  140  if it is desired to cause the actuator device  100  to default to the mode position shown in  FIG. 5 . If the middle mode position shown in  FIG. 6  is the default mode position, a second piston spring  150  may be provided opposite the first piston spring  150  to apply spring forces to the piston  140  in opposite directions. Depending on the particular implementation, the spring constants k of the piston springs  150  may be varied to default the actuator device  100  to any position between the end positions shown in  FIGS. 5 and 7 . In still further embodiments, the piston spring  150  may be omitted and the actuator device  100  will not have a default mode position. 
         [0033]    In the illustrated embodiment, the position of the piston  140 , the cam actuator bar  102  and, correspondingly, the actuator cam  60  will be dictated by a first pressure P 1  at the first fluid passage  132 , a second pressure P 1  at the second fluid passage  134 , and the amount of compression of the piston spring  150 . The first pressure P 1  acts on the piston body  142  to exert a first pressure force F 1  to the right in as seen in  FIG. 5 , and has a magnitude equal to P 1 ×A 1 , where A 1  is the cross-sectional area of the right side of the piston body  142 . The second pressure P 2  acts on the opposite side of the piston body  142  to exert a second pressure force F 2  on the piston  140  to the left. The second pressure force F 2  has a magnitude equal to P 2 ×A 2 , where A 2  is the cross-sectional area of the left side of the piston body  142 . In the illustrated embodiment, the area A 1  is equal to the area A 2 . In other implementations, the area A 1  and the area A 2  may be different depending on the configuration of the piston  140  and its connection to the piston housing  110 . In either configuration, the equations and relationships discussed hereinafter will have equal applicability. Finally, the piston spring  150  exerts a spring force FS on the piston  140  to the right having a magnitude equal to kX, where k is the spring constant for the piston spring  150  and X is the amount of compression of the piston spring  150 . It is contemplated that the spring constant k will have a constant value over the operating range of the actuator device  100 . 
         [0034]    In the present example, the first pressure P 1  may have a value that is approximately constant and equal to a system pressure of the vehicle that is known to the control system causing changes in the position of the actuator device  100  and the mode of the multimode clutch  10 . The second pressure P 2  may be a control pressure that may be varied by controlling an output pressure of a pressurized hydraulic fluid source (not shown) in fluid communication with the second fluid passage  134 . As a result, the second pressure P 2  is controlled and varied to move the piston  140  and the cam actuator bar  102 . 
         [0035]    As seen in  FIG. 5 , the piston  140  is moved to the left with the first piston stop  144  engaged by cap  126 . In this position, the cam actuator bar  102  has moved the actuator cam  60  to the first mode position shown in  FIG. 2 . The force equation for this position may be expressed as F 1 +FS≦F 2 , or P 1 *A 1 +kX≦P 2 *A 2 . Holding the second pressure P 2  constant, or increasing the second pressure P 2 , will maintain the piston  140  at the left limit position and keep the multimode clutch  10  in the first mode. 
         [0036]    When a controller (not shown) of the vehicle detects that the multimode clutch  10  should move to a second mode such as that shown in  FIG. 3 , the controller may cause the pressurized hydraulic fluid source to reduce the second pressure P 2 . When the force equation changes to F 1 +FS&gt;F 2 , or P 1 *A 1 +kX&gt;P 2 *A 2 , the first pressure force F 1  and the spring force FS may overcome the second pressure force F 2  and cause the piston  140  to begin to move to the right toward the second mode position shown in  FIG. 6 . As the piston  140  moves toward the second mode position, the controller may receive position sensor signals from a position sensor (not shown) containing values indicating a sensed position of a component of the multimode clutch  100 , the actuator device  100  or other component that is indicative of the state of the actuator cam  60  in transitioning from the first mode position to the second mode position. For example, the position sensor may be operatively connected to the actuator cam  60 , the actuator tab  84  or the cam actuator bar  102 . Upon receiving the position sensor signals, the controller may further adjust the second pressure P 2  as necessary arrive at and maintain the piston  140  at the second mode position of  FIG. 6 . 
         [0037]    Once the piston  140  and, correspondingly, the actuator cam  60  arrive at the second mode position, the controller may set the second pressure P 2  at a value that restores the force equation to equilibrium such that F 1 +FS=F 2 , or P 1 *A 1 +kX=P 2 *A 2 . It will be apparent that the spring force FS is less at the second mode position due to the elongation of the piston spring  150 . Correspondingly, the second pressure P 2  and the second pressure force F 2  will be less than at the first mode position of  FIG. 5 . From the second mode position, the second pressure P 2  may be decreased to cause the piston  140  to move to the right toward the third mode position of  FIG. 7 , or increased to cause the piston  140  to move to the left and return to the first mode position of  FIG. 5 . 
         [0038]      FIGS. 8-10  illustrate an alternative embodiment of the actuator device  100  configured to be operatively connected to a multimode clutch  10  having an actuator cam  160  with an actuator tab  184  extending therefrom. The actuator cam  160  may operate in a similar manner as the actuator cam  60  to switch the multimode clutch  10  between mode positions as the actuator cam  160  is rotated about a rotational axis of the multimode clutch  10 . The piston housing  110  may have a similar configuration as described above. A piston  190  may be disposed within the longitudinal bore  112  and slidable back and forth in the longitudinal direction within the longitudinal bore  112 . The piston  190  may have generally the same configuration as the piston  140  described above, and may include a piston body  192  having a first piston stop  194  and a second piston stop  196  extending outwardly longitudinally from opposite sides of the piston body  192  to limit the travel of the piston  190  in each direction in the manner described above. The piston body  192  may have a piston body outer diameter that is less than the inner diameter of the main bore portion  120  so that the piston  190  may slide therein without leakage of hydraulic fluid there between. If necessary, appropriate seals (not shown) may be provided at the interface between the main bore portion  120  and the piston body  192  to further prevent leakage of hydraulic fluid. 
         [0039]    The piston  190  may be configured to engage the actuator tab  184  by providing an annular groove  198  at approximately the longitudinal center of the piston body  192 . The annular groove  198  may be sufficiently wide and deep so that the actuator tab  184  may be inserted through the longitudinal slot  104  and received by the annular groove  198 . The actuator tab  184  may be rounded to facilitate rotation of the actuator tab  184  within the annular groove  198 , and rotation of the actuator cam  160  about the rotational axis of the multimode clutch  10 , as the piston  190  moves from the first mode position of  FIG. 8 , past the second mode position of  FIG. 9  and to the third mode position of  FIG. 10 . 
         [0040]    The embodiment of  FIGS. 8-10  further illustrates the use of piston springs  150  on both sides of the piston  190  so that the actuator device  100  may have a default mode position that is between the first mode position and the third mode position. The second piston spring  150  may be taken into accounted in the control strategy by adding a second spring force FS 2  to the force equation acting in the same direction as the second pressure force F 2 . In other respects, the control strategy for the multimode clutch  10  and the actuator device  100  may perform substantially as described above. 
       INDUSTRIAL APPLICABILITY 
       [0041]    The illustrated configuration of the actuator device  100  and the control strategy for changing the position of the actuator device  100  discussed herein may be advantageous in applications where a selectable clutch has four or more clutch modes. The actuator device  100  provides infinite mode positions that will be dictated by the pressures, the cross-sectional areas of the pistons  140 ,  190 , and the spring forces applied by the piston spring(s)  150 . Those skilled in the art will understand that the control strategy for the actuator device  100  may be configured stop the pistons  140 ,  190  at additional intermediate mode positions at which a different engagement mode will be provide between the components connected by the selectable clutch. By creating an actuator device  100  wherein the pistons  140 ,  190  can be positioned using differential pressures within the piston housing  110 , three or more modes for the multimode clutch  10  can be achieved by changing the pressure differential acting on the single piston  140 ,  190 . 
         [0042]    Those skilled in the art will further understand that the configuration of the actuator device  100  and the control strategy described herein are exemplary, and modifications of the design are contemplated. For example, in alternative embodiments, the second pressure P 2  may be held constant and the first pressure P 1  may be controlled to move the piston  140  to the right (increase the first pressure P 1 ) and to the left (decrease the first pressure P 1 ). In further alternatives, both pressures P 1 , P 2  may be controlled so that a pressure differential is varied to move the piston  140 . Such variations are contemplated by the inventors as having use in actuator devices in accordance with the present disclosure. 
         [0043]    The design may be further varied in terms of the location and presence of the piston spring(s)  150 . The piston spring  150  may be moved to other locations in and around the actuator device  100  while still having an effect on the response and control of the pistons  140 ,  190 . For example, the piston spring  150  in  FIGS. 5-7  could be moved to the opposite side of the piston  140  and positioned between the piston  140  and the closed end wall  148 . In this position, the piston spring  150  would bias the piston  140  toward the one-way locked, one-way unlocked position of  FIG. 5 . In these embodiments, the spring force FS would be subtracted from the first pressure force F 1  in the equations discussed above. With the spring force FS assisting the second pressure force F 2  in moving the piston  140  to the left, lower second pressures P 2  will need to be generated to move the piston  140  between the locking positions. 
         [0044]    In other embodiments, the piston spring  150  may be located external to the piston housing  110 , and still be operatively connected to the cam actuator bar  102  ( FIGS. 5-7 ) to provide the spring force FS to the piston  140 . For example, the piston spring  150  may be coupled between a stationary portion of the vehicle, such as the vehicle frame, and the cam actuator bar  102 . Alternatively, the piston spring  150  may be connected between the stationary structure and the cam actuator  60 ,  160  that will transfer the spring force FS of the piston spring  150  to the pistons  140 ,  190  through the intervening connection provided by the cam actuator bar  102  ( FIGS. 5-7 ) or the actuator tab  184  and the annular groove  198  ( FIGS. 8-10 ). Such external arrangements of the piston spring  150  can function to apply the spring force FS in either direction to either work against or assist the second pressure force F 2  in moving the pistons  140 ,  190  between the locking positions, or in both directions to bias the pistons  140 ,  190  toward an intermediate locking position. 
         [0045]    As discussed above, in further alternative embodiments, the piston spring  180  may be omitted so that no spring force FS acts on the piston  150 . In such embodiments, the controlled first pressure P 1  will be adjusted accordingly to reflect the absence of the spring force FS from the force balancing equations discussed above. With the spring force FS omitted, the curve of the graph  190  will move downward by an amount that is less than in the situation above where the spring force FS is shifted to assisting the first pressure force F 1 , but removal of the piston spring  180  will still lower first pressures P 1  required to move the piston  150  between the locking positions. 
         [0046]    While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection. 
         [0047]    It should also be understood that, unless a term was expressly defined herein, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to herein in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning.