Patent Publication Number: US-8528950-B2

Title: Latch mechanism and latching method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/337,222, filed Feb. 1, 2010, and to U.S. Provisional Patent Application No. 61/353,720, filed Jun. 11, 2010, the entire contents of both of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The present invention relates to latch mechanisms, such as those used in automotive applications including, but not limited to, vehicular rear hatches, trunks, and doors. 
     SUMMARY 
     In some embodiments, the invention provides a latch releasably engagable with a striker having a trajectory defined between a latched position and an unlatched position. A catch is pivotable about a first axis and has first and second grooves, and a pawl is pivotable about a second axis that can be parallel to the first axis. The first groove of the catch is positioned to releasably receive the striker, and the second groove of the catch is positioned to receive a portion of the pawl. When, for example, the latch is driven to a latched state in a cinching operation, the portion of the pawl can cam across an interior surface of the second groove to rotatably drive the catch to a latched position. Alternatively or in addition, when the latch is released and the catch is rotated toward an unlatched position under the bias of a catch spring and/or the striker, the portion of the pawl can cam across the interior surface of the second groove as the catch is rotated toward the unlatched position. When, for example, the latch is powered to an unlatched state by a motor driving the pawl or under the bias of a pawl spring, the portion of the pawl can cam across another interior surface of the second groove to rotatably drive the catch toward an unlatched position. Alternative or in addition, when the striker drives the catch to rotate the catch toward a latched position, this other interior surface of the second groove can be cammed against the portion of the pawl to rotatably drive the pawl toward a latched position. 
     Some embodiments of the present invention provide a latch and method of latching a latch in which a striker moveable along a trajectory is releasably engaged with a catch that is rotatable about a first axis between a latched state and an unlatched state, and in which a pawl rotatable about a second axis is positioned for engagement with the catch, wherein the catch can be rotatably driven from an unlatched state to a latched state by movement of the striker or by rotation of the pawl, and wherein the pawl is rotatable to a position in which the pawl blocks rotation of the catch from the latched state to the unlatched state. 
     In some embodiments, a latch releasably engagable with a striker is provided, and includes a catch pivotable about a first axis between a latched position in which the catch retains the striker, and an unlatched position, and a pawl pivotable about a second axis, wherein the catch is responsive to force from the striker and the pawl to pivot from an unlatched position to a latched position of the catch, and is responsive to movement of the pawl (and in some cases force exerted by the pawl) to pivot from the latched position to the unlatched position of the catch. 
     Some embodiments of the present invention provide a latch and latching method in which a catch is rotated about a first axis from an unlatched state in which the catch can receive a striker, to a latched state in which the catch releasably retains the striker against removal from the latch, and a pawl rotated about a second axis and in camming contact across with a surface of the catch from the unlatched state of the catch to the latched state of the catch to drive the catch from the unlatched state to the latched state. 
     In some embodiments, a latch releasably engagable with a striker is provided, and includes a catch pivotable about a first axis between a latched position in which the catch retains the striker, and an unlatched position, and a pawl pivotable about a second axis, wherein the pawl is rotatable in a first direction to generate rotation of the catch from the latched position to the unlatched position, and is rotatable in a second direction opposite the first direction to generate rotation of the catch from the unlatched position to the latched position. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a prior art latch in a latched state with basic force vectors applied. 
         FIG. 2  illustrates a latch according to an embodiment of the present invention, the latch being shown in a latched state with basic force vectors applied. 
         FIGS. 3A-3D  illustrate a sequence of the latch of  FIG. 2  transitioning from the latched state to an unlatched state. 
         FIG. 4  illustrates the prior art latch of  FIG. 1 , shown with vectors illustrating various motive forces for moving the latch components. 
         FIG. 5  illustrates the latch of  FIG. 2 , shown with vectors illustrating various motive forces for moving the latch components. 
         FIG. 6  is a front view of a power latch assembly utilizing the latch of  FIG. 2 , the power latch assembly being shown in an unlatched state. 
         FIG. 7  is an exploded assembly view of the power latch assembly of  FIG. 6 . 
         FIGS. 8A-8D  illustrate a cinching action carried out by the power latch assembly of  FIG. 6 . 
         FIGS. 9A-9D  illustrate a power release action carried out by the power latch assembly of  FIG. 6 . 
         FIGS. 10A and 10B  illustrate a manual latching action carried out by the power latch assembly of  FIG. 6 . 
         FIGS. 11A and 11B  illustrate a manual release action carried out by the power latch assembly of  FIG. 6 . 
         FIG. 12  is a front view of a power latch assembly similar to that of  FIG. 6 , the power latch assembly being shown in a latched state. 
         FIG. 13A  is a front view of a residual magnet latch assembly utilizing the latch of  FIG. 2 , the residual magnet latch assembly being shown in an unlatched state. 
         FIG. 13B  is a front view of the residual magnet latch assembly of  FIG. 13A , shown in a latched state. 
         FIGS. 14 and 15  schematically illustrates the operation of a residual magnet. 
         FIG. 16  is an exploded view of a toroidal residual magnet used in the residual magnet latch assembly of  FIGS. 13A and 13B . 
         FIG. 17  is a cross-sectional view of the toroidal residual magnet of  FIG. 16 , shown in a first state. 
         FIG. 18  is a cross-sectional view of the toroidal residual magnet of  FIG. 16 , shown in a second state. 
         FIG. 19  is a front view of a manual latch assembly utilizing the latch of  FIG. 2 , the manual latch assembly being illustrated in a latched state. 
         FIGS. 20A and 20B  illustrate an alternate latch substitutable for the latch of  FIG. 2  in the various latch assemblies disclosed herein. 
         FIG. 21  illustrates a latch according to an embodiment of the present invention, the latch being shown in an unlatched state. 
         FIG. 22  illustrates the latch of  FIG. 21  in a transition state between latched and unlatched states. 
         FIG. 23  illustrates the latch of  FIG. 21  in the latched state. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the present invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
       FIG. 1  illustrates a conventional latch  40  which may be used to selectively hold shut an item such as a door (e.g., a vehicle door, hatch, decklid or trunk, and the like). The latch  40  includes a catch  44  and a pawl  48 . As is common in conventional latches, the catch  44  is rotatable about a first axis A 1  to selectively engage and trap a striker  52  within a groove  54  formed in the catch  44 , whereas the pawl  48  is positioned adjacent the catch  44  and is pivotable about a second axis B 1  parallel with the first axis A 1  of the catch  44 . The pawl  48  has a flat engagement surface  56  configured to engage a corresponding flat engagement surface  60  of the catch  44  to retain the catch  44  in the latched position of  FIG. 1 , keeping the striker  52  retained within the groove  54 . In the case of automotive doors and the like, the striker  52  may be fixed to a door frame and the latch  40  may be mounted at the edge of a door that is swingable relative to the door frame, although these positions of the striker  52  and latch  40  can be reversed in other embodiments. The door is opened by releasing the pawl  48  from the engaged position of  FIG. 1  so that the catch  44  can rotate about the first axis A 1  to free the striker  52 . When the door is swung closed, the striker  52  is forced into the groove  54 , thereby rotating the catch  44  toward the latched position of  FIG. 1 . The pawl  48  is typically spring-biased toward the latched position of  FIG. 1  so that it automatically locks the catch  44  in the latched position. 
     In a tight-fitting door, such as a vehicle door with a compressible weather strip between the door frame and the door, the striker  52  exhibits a force on the catch  44  as shown by arrow F 1  in  FIG. 1 . Similar forces can be present under certain extreme conditions of the latch  40 , such as under impact, under inertial loading resulting from a vehicle rollover or other accident, and the like. The force F 1  from the striker  52  is offset from the first axis A 1 , and urges the catch  44  in a counterclockwise direction to exhibit a force (arrow F 2  in  FIG. 1 ) on the pawl  48 . The pawl  48  exhibits a reaction force (arrow F 3  of  FIG. 1 ) that keeps the catch  44  from rotating out of the latched position of  FIG. 1 . Although surface contact exists between the engagement surfaces  56 ,  60 , the pressure between the surfaces can be resolved to theoretical point loads for analysis as shown in  FIG. 1 . The line of the forces F 2  and F 3  is generally aligned with the pawl&#39;s axis B 1  or is spaced from the axis B 1  in a direction toward the catch  44  to make the pawl  48  stable against accidental release as the striker  52  bears against the catch  44 . 
       FIG. 2  illustrates a latch  80  according to an embodiment of the present invention. The illustrated latch  80  includes a catch  84  and a pawl  88 . The catch  84  is rotatable about a first axis A 2  (defined by a first axle, pivot, or pin—hereinafter referred to simply as “pin”  90  for ease of description) to selectively engage and trap a striker  52  within a groove  94  defined in a body of the catch  84 . The pawl  88  is positioned adjacent the catch  84  and is pivotable about a second axis B 2  (defined by a second axle, pivot, or pin—hereinafter referred to simply as “pin”  96  for ease of description) that can be parallel with the first axis A 2  of the catch  84 . The striker  52  may exhibit a force on the catch  84  as shown by arrow F 1  in  FIG. 2  when latched, such as by a compressed door seal or from any other source as described above. The force F 1  from the illustrated striker  52  is offset from the first axis A 2  and urges the catch  84  in a counterclockwise direction to exhibit a force (arrow F 2  in  FIG. 2 ) on the pawl  88 . The pawl  88  exhibits a reaction force (arrow F 3  of  FIG. 2 ) that keeps the catch  84  from rotating out of the latched position of  FIG. 2 . The line of the forces F 2  and F 3  in the illustrated embodiment is substantially aligned with the pawl&#39;s axis B 2  so that the pawl  88  is stable against movement from the latched position of  FIG. 2  as the striker  52  bears against the catch  84 . Regardless of the magnitude of the forces F 2  and F 3 , no rotational load is applied to the pawl  88  when the forces F 2  and F 3  are aligned with the pawl&#39;s axis B 2 . It will also be appreciated that negligible or very little rotational load is applied to the pawl  88  when the forces F 2  and F 3  are generally aligned with the pawl&#39;s axis B 2 . 
     Rather than flat engagement surfaces between the catch  84  and the pawl  88 , the pawl  88  of the embodiment in  FIG. 2  is provided with a roller  98  (e.g., a roller bearing), and the catch  84  is provided with a contoured cam surface  102 . In the illustrated construction, the cam surface  102  forms part of a groove  106  in the catch  84  in which a portion of the pawl  88  is received. In some embodiments, the portion of the pawl  88  can be an appendage or other protrusion of the pawl  88 . As described in further detail below, the engagement between the roller  98  and the cam surface  102  offers operational features and benefits unattainable with the traditional latch  80 . Unlike the conventional latch  40  of  FIG. 1 , a low friction engagement is established between the catch  84  and the pawl  88  due to the roller  98 . Among other things, the low friction engagement allows easier movement of the pawl  88  away from the latched position. Also, a stable latched state of the pawl  88  and catch  84  is provided by the contoured cam surface  102 . 
     The cam surface  102  of the catch  84  in  FIG. 2  has a first portion  102 A with a curvature that is concentric or generally concentric with the axis B 2  of the pawl  88  when the catch  84  is in the latched position. This relationship is what allows the forces F 2 , F 3  between the catch  84  and the pawl  88  to be aligned with the axis B 2  of the pawl  88  in the latched state. A second portion  102 B of the cam surface  102  is non-concentric with the axis B 2  of the pawl  88  in the latched state. In the illustrated embodiment of  FIG. 2 , the second portion  102 B makes up a majority portion of the cam surface  102  along which the pawl  88  moves and contacts in at least one operation of the latch  80 . Although the cam surface  102  transitions smoothly between the first portion  102 A and the second portion  102 B, the second portion  102 B acts as a camming portion by which motion of at least one of the catch  84  and the pawl  88  is operable to drive the motion of the other. This results in a fundamentally different type of movement compared with the conventional latch  40  of  FIG. 1 . 
     The catch  84  and the pawl  88  of the latch  80  are co-drivable (i.e., movement of either one can drive movement of the other). For example, the catch  84  and the pawl  88  of  FIG. 2  can move together, or “synchronously” substantially throughout the movement of the latch  80  from the latched position to the unlatched position and vice versa, whereas the pawl  48  of the conventional latch is simply removed from the catch  44  for unlatching, and has no corresponding motion during movement of the catch  44  between its latched and unlatched positions. As used herein, the term “synchronously” means that, in a range of motion of one element, the other element has a corresponding range of motion, and in which each position of each element at least partially defines a corresponding position of the other element. In some embodiments of the present invention, this synchronous motion between the catch  84  and pawl  88  exists throughout the range of movement of the pawl  88  or catch  84  (and in some embodiments, throughout the range of movement of both the pawl  88  and catch  84 ) between the latched and unlatched states of the latch  80 . In other embodiments, this synchronous motion between the catch  84  and pawl  88  exists throughout at least a majority of the range of movement of the pawl  88  or catch  84  (and in some embodiments, throughout at least a majority of the range of movement of both the pawl  88  and catch  84 ) between the latched and unlatched states of the latch  80 . 
     The synchronous movement of the catch  84  and the pawl  88  of the illustrated latch  80  from the latched position of the latch  80  ( FIG. 3A ) to the unlatched position of the latch  80  ( FIG. 3D ) is illustrated in  FIGS. 3A to 3D , and operation of the latch  80  is described below with reference to these figures, it being understood that in the illustrated embodiment and in other embodiments, similar synchronous movement of the catch  84  and the pawl  88  of the latch  80  from the unlatched position of the latch  80  to the latched position of the latch  80  is possible. 
     As shown in  FIG. 3A , the striker  52  of the illustrated embodiment is retained within the groove  94  of the catch  84 , and the roller  98  of the pawl  88  is in contact with the first portion  102 A of the cam surface  102 . In this position, downward force from the striker  52  does not cause counterclockwise rotation of the catch  84  to the unlatched position, since the pawl  88  provides the requisite reaction force to prevent movement of the catch  84  from the latched position of  3 A. When it is desired to release the latch  80 , the pawl  88  is rotated clockwise so that the roller  98  is moved from the first portion  102 A to the second portion  102 B of the cam surface  102 . Movement of the roller  98  along the second portion  102 B of the cam surface  102  causes corresponding synchronous movement of the catch  84 . Unlike the conventional latch  40 , the catch  84  and the pawl  88  of the latch  80  rotate in opposite directions as the latch  80  is released. After traversing the second portion  102 B of the cam surface  102  in the unlatching direction, the roller  98  may leave the cam surface  102  and contact an adjacent surface  110  of the groove  106  in the fully unlatched position ( FIG. 3D ). In this position, the striker  52  is free to be removed from the catch  84 . 
     In some embodiments, the catch  84  is spring-biased to an unlatched position in at least a portion of the range of rotational movement of the catch  84 , such as by a spring (not shown) coupled to the catch  84 . Therefore, as the pawl  88  in the illustrated embodiment of  FIGS. 3A-3D  is rotated toward an unlatched position, the catch  84  is likewise biased toward and moves toward its unlatched position. In other embodiments, however, the catch  84  is not biased toward its unlatched position. In these and other embodiments, the pawl  88  (e.g., the roller  98  of the pawl  88 ) can rotate to move into contact with a surface  110  of the catch  84  in order to cam against and rotate the catch  84  toward its unlatched position. In such cases, the surface  110  of the catch  84  against which the pawl  88  cams in this manner can at least partially define a groove  106  of the catch  84  as described above, and in some embodiments can at least partially define a side of a groove  106  opposite the cam surface  102 . 
     To return to the latched position of the latch  80  illustrated in  FIGS. 3A-3D , the above-described process is reversed, beginning with the striker  52  contacting the catch  84  and initiating rotation of the catch  84  about its axis A 2  in the clockwise direction. This demonstrates how the catch  84  and the pawl  88  not only have synchronous movement, but can furthermore have bi-directional synchronous movement by which either of the catch  84  and the pawl  88  is operable to rotate the other. Rotation of the illustrated catch  84  toward the latched position can bring the surface  110  of the catch  84  into engagement with the roller  98  of the pawl  88  (if this engagement has not already been established), after which time further rotation of the catch  84  drives rotation of the pawl  88  in the counterclockwise direction about its axis B 2  toward the latched position. In this case, the pawl  88  (e.g., roller  98 ) can contact and cam along the cam surface  102  of the catch  84 , and in some embodiments can return to a position engaged with the first portion  102 A of the cam surface  102 . The catch  84  and the pawl  88  may be returned to their latched positions solely by the manual action of the striker  52 , or in combination with one or more active or passive assist devices, such as a motor or other powered actuator, or a spring (e.g., an over-center spring). 
     As illustrated in  FIG. 4 , various forces may be applied to the catch  44  and the pawl  48  of the conventional latch  40 . In the most basic manual operation, a manual closing force F 4  is applied to the catch  44  via the striker  52  to drive the catch  44  from the unlatched position (not shown) to the latched position. Likewise, a manual opening force F 5  may be applied to the pawl  48  to pull the pawl  48  out of engagement with the catch  44 . It should be noted that even when the manual opening force F 5  is sufficient to retract the pawl  48 , another force must typically be applied to the catch  44  to effect movement of the catch  44  to the unlatched position, since the pawl  48  is not capable of driving the catch  44  to the unlatched position. 
     With continued reference to  FIG. 4 , the conventional latch  40  may also be used in a powered latch assembly. When the conventional latch  40  is used in a powered latch assembly, the pawl  48  can be released or disengaged from the catch  44  by a first torque T 1  applied to the pawl  48 . Movement of the catch  44  to the unlatched position is then dependent upon a release force applied by the striker  52  itself or another force applied directly to the catch  44 . If it is desired to allow powered cinching of the striker  52  with the catch  44 , a second torque T 2  must be applied directly to the catch  44  (i.e., not applied to the catch  44  via the pawl  48 ). 
       FIG. 5  illustrates at least one aspect of how the latch  80  of  FIG. 2  differs from the conventional latch  40  of  FIGS. 1 and 4 . While a manual closing force F 6  from the striker  52  can drive motion of the illustrated catch  84  toward the latched position, and a manual opening force F 7  can be applied to the pawl  88  for releasing the catch  84 , the manual opening force F 7  can be significantly less than the manual opening force F 5  required to release the pawl  48  of the conventional latch  40 . Because the illustrated catch  84  and pawl  88  have a cam and cam-follower engagement, rather than flat engagement surfaces that contact when latched, the friction that must be overcome to move the pawl  88  from its latched position can be significantly lower than that of the conventional latch  40 . Furthermore, the illustrated pawl  88  is provided with the roller  98  for rolling across the cam surface  102 , thereby significantly reducing friction by substantially eliminating sliding or dragging action between the catch  84  and the pawl  88 . 
     In the illustrated embodiments of  FIGS. 2 ,  3 , and  5 , the cam surface  102  of the catch  84  has a generally concave shape facing the pawl  88 . This concave shape of the first portion  102   a  of the cam surface  102  can enable an enhanced degree of stability between the catch  84  and the pawl  88  when the catch  84  and pawl  88  are in a latched state by reducing or eliminating forces that would otherwise urge these elements to move toward their unlatched positions. This stability can be enhanced when used in conjunction with the concentricity of the cam surface  102  about the axis of rotation B 2  of the pawl  88  as described above—another feature that reduces or eliminates forces urging the catch  84  and pawl  88  from their latched positions. 
     The generally concave shape of the second portion  102   b  can provide significant mechanical advantage when the pawl  88  is used to drive the catch  84  to a latched state, as will be described in greater detail below. Although the shapes of the cam surfaces  102   a ,  102   b ,  110  described and illustrated herein can provide significant benefits in various latch embodiments according to the present invention, in other embodiments, any or all of the cam surfaces  102   a ,  102   b ,  110  can instead be flat, convex, or can have any other shape desired that is capable of transferring mechanical force between the catch  84  and the pawl  88  as described herein. 
     With further reference to  FIG. 5 , a first torque T 3  may be applied to the pawl  88  by a powered actuator to move the pawl  88  from its latched position to its unlatched position when the latch  80  is used in a powered latch assembly. Movement of the catch  84  toward the unlatched position can then be automatically effected since the catch  84  and the pawl  88  exhibit synchronous motion as discussed above. Aside from the camming force from the pawl  88  and/or a spring force or other biasing force upon the catch  84  toward an unlatched position (and also the force which may inherently exist from the striker  52  bearing on the groove  94  of the catch  84  in a tight-fitting door, or the like), no additional force needs to be applied to the catch  84  by any other means for unlatching and releasing the striker  52 . If it is desired to also enable powered cinching of the striker  52  with the catch  84 , a second torque T 4  may be applied to the pawl  88  and transferred to the catch  84 . This negates the need for separate actuators or the complicated transmission mechanism that can be necessary to separately power both the pawl and the catch with a single actuator. Thus, the size of a powered latch assembly using the latch  80  is reduced and the number of parts and the degree of complexity can be reduced. Also, the number of inputs to the latch  80  (i.e., sources of force for actuating elements of the latch  80 ) can be reduced by virtue of the fact that the pawl  88  can be moved in opposite directions to perform different functions (e.g., a powered cinching input to the pawl  88 , as described in more detail below, and a catch release input to the pawl  88 , as described above). The second portion  102 B of the cam surface  102  can also provide a significant mechanical advantage (e.g. 10:1) for amplifying the cinching torque present on the catch  84  for a given torque T 4  available at the pawl  88 . 
       FIGS. 6-11B  illustrate a powered latch assembly  200  including the latch  80  of  FIG. 2 . In this embodiment, the catch  84  and the pawl  88  are rotatably mounted at least partially within a housing  204 . As shown in  FIG. 7 , the housing  204  is sandwiched between a frame plate  205 A and a support plate  205 B, both of which are riveted to the housing  204  in the illustrated construction. The housing  204  includes an opening  206  allowing entry of the striker  52  into the groove  94  of the catch  84  for latching. Both the catch  84  and the pawl  88  are rotatable relative to the housing  204  about their respective axes A 2 , B 2  as described above. In this embodiment, an over-center spring  208  is coupled between the pawl  88  and the housing  204 , and urges the pawl  88  to the latched position or the unlatched position depending upon the particular orientation of the pawl  88  in relation to the over-center spring  208 . With further reference to the illustrated embodiment of  FIGS. 6-11B , a sensor  212  is provided in the housing  204  to sense the position of the pawl  88 . The illustrated pawl  88  includes a portion  216  that contacts the sensor  212  (e.g., a push-type contact switch or other suitable switch) when the pawl  88  is in the unlatched position ( FIG. 6 ) so that the sensor  212  is operable to generate a signal indicative of whether the pawl  88  is in the unlatched position. The signal may be transmitted to a controller  218 . It should be noted that other types of sensors, including non-contact type sensors, may be used to determine whether the pawl  88  is in the unlatched position. In some embodiments, the sensor  212  or any number of other sensors can be positioned and adapted to sense (and generate corresponding signals) more specific information regarding the position of the pawl  88  or other elements of the latch  80 . For example, a sensor may positively sense the achievement of both the latched and unlatched positions of the pawl  88  and generate corresponding signals. 
     With reference now to  FIG. 7 , the illustrated power latch assembly  200  is shown in greater detail. In the illustrated embodiment, the pawl  88  is constructed of multiple individual pieces. As shown in  FIG. 7 , the pawl  88  can be constructed of two plate-like members  88 A,  88 B separated by at least one spacer  88 C integral with and/or separate from the plate-like members  88 A,  88 B. The roller  98  is positioned on a post  88 D that is integral with a first of the plate-like members  88 A. In other embodiments, the pawl  88  is constructed of fewer elements, such as a single integral element comprising the plate-like members  88 A,  88 B and spacers  88 C shown in  FIG. 7  and carrying a roller  98  as described above. Alternatively, the pawl  88  can be constructed of a single plate-like member of any suitable thickness shaped to carry the roller  98  and defining the portion  216  positioned to trigger the sensor  212  as described above, or a body otherwise adapted to perform these functions. In still other embodiments, one or more portions of a pawl body can define the camming element or surface used to cam with the catch  84 . Still other pawl arrangements and constructions are possible, and fall within the spirit and scope of the present invention. 
     In some embodiments of the present invention, it is desirable to provide a lost motion connection between the pawl  88  and a primary mover of the pawl  88  (e.g., a motor  228  in the illustrated embodiment as described below, a solenoid, or other actuator positioned to drive and rotate the pawl  88 ). This lost motion can enable movement of the pawl  88  independent of movement of the primary mover—a feature that can be useful in embodiments in which the pawl  88  can be moved by the catch  84  (for example). The lost motion connection between the primary mover and the pawl  88  can take various forms depending at least in part upon the type of primary mover used and the position of the primary mover in the latch assembly  200 . 
     By way of example only, the lost motion connection in the illustrated latch assembly  200  of  FIGS. 6-11B  is provided by a bi-directional driver  220  positioned and shaped to drive rotation of the pawl  88  in either a clockwise direction or a counterclockwise direction. In the illustrated embodiment, the driver  220  is rotatably mounted upon the same pin  96  as the pawl  88  (and therefore can rotate about the same axis B 2  as the pawl  88 ), although in other embodiments this need not necessarily be the case. By virtue of the lost motion connection between the illustrated driver  220  and the pawl  88 , the exact amount of rotation of the driver  220  may not be transferred to the pawl  88  in all circumstances. As shown in  FIG. 7 , the illustrated driver  220  includes first and second protrusions  224 A,  224 B that selectively engage the pawl  88  to drive rotation thereof. The first protrusion  224 A of the illustrated driver  220  is configured to drive the pawl  88  counterclockwise (toward the latching position), and the second protrusion  224 B is configured to drive the pawl  88  clockwise (toward the unlatching position). In the illustrated embodiment, the driver  220  is biased to a neutral position ( FIG. 6 ) by a torsion spring  226  ( FIG. 7 ), although any other suitable biasing elements or devices can be used for this purpose, such as magnets or electromagnets, extension springs, elastic bands, and the like. 
     The driver  220  in the embodiment of  FIGS. 6-11B  is moved by a powered actuator  228  to rotate and drive the pawl  88 . In the illustrated embodiment, the actuator  228  is an electric motor that drives a toothed portion  232  of the driver  220  through a gear train  236 . The illustrated gear train  236  includes a plurality of gears that reduce the speed of the actuator  228  and increase the torque. The gear train  236  can be configured to provide a large cinching torque to the driver  220  and the pawl  88 , and ultimately to the catch  84  for cinching the striker  52 , while using a relatively lightweight and low power actuator  228 . In the illustrated embodiment, the final gear of the gear train  236  is a worm gear  240  that engages the toothed portion  232  of the driver  220 , and enables the driver  220  to be rotated about an axis perpendicular to the worm gear  240 . In other embodiments, any other number, orientation, and arrangement of gears in the gear train  236  can instead be used, as can other mechanical power transmission assemblies adapted to transfer mechanical power from the prime mover to the driver  220 . 
       FIGS. 8A-8D  illustrate the latching and power cinching sequence of the power latch assembly  200  of  FIG. 6 . Beginning at  FIG. 8A , the catch  84  and the pawl  88  are in their respective unlatched positions. In this state, the designated portion  216  of the pawl  88  is in contact with the sensor  212 , and the roller  98  of the pawl  88  is in contact with or in close proximity to the surface  110  adjacent the cam surface  102 . The driver  220  is in a neutral or “home” position. The groove  94  in the catch  84  is in registry with the opening  206  in the housing  204  so that the striker  52  is able to enter the groove  94  through the opening  206 . As indicated by the arrow in  FIG. 8A , the striker  52  is received into the groove  94  of the catch  84 . This may occur through movement of the striker  52 , or through movement of the powered latch assembly  200  (e.g., with a swingable door, hatch, decklid, etc.) toward the striker  52 . 
     As shown in  FIG. 8B , the striker  52  has further entered the opening  206  and the groove  94  of the catch  84  relative to its position in  FIG. 8A . This movement of the striker  52  drives rotation of the catch  84  in the clockwise direction. Rotation of the catch  84  in the clockwise direction drives counterclockwise rotation of the pawl  88  as the surface  110  contacts the roller  98 . This movement of the pawl  88  moves the portion  216  of the pawl  88  off of the sensor  212 , which in turn transmits a signal to the controller  218  (see  FIG. 6 ) that the striker  52  is now present in the groove  94  of the catch  84 . Upon receipt of this signal from the sensor  212 , the controller  218  sends a command signal to the actuator  228  to begin actuation. It should be noted that the over-center spring  208  may be overcome either before or after actuation by the actuator  228  begins. When the bias of the over-center spring  208  is overcome (i.e., the bias urging the pawl toward the unlatched position), the pawl  88  is biased by the over-center spring  208  toward the latched position. 
     Between the state illustrated in  FIG. 8B  and that illustrated in  FIG. 8C , the bias of the over-center spring  208  urging the pawl  88  toward the unlatched position is overcome, and the spring  208 , along with the driver  220 , drive rotation of the pawl  88  (and the catch  84 ) toward the latched positions of the pawl  88  and catch  84 . During powered actuation by the actuator  228  in the illustrated embodiment, the worm gear  240  drives counterclockwise rotation of the driver  220  by engaging the toothed portion  232  of the driver  220 . The driver  220  in turn drives the pawl  88  via the first protrusion  224 A. As the actuator  228  moves the driver  220  to rotate the pawl  88 , the roller  98  of the pawl  88  contacts the second portion  102 B (see  FIG. 7 ) of the cam surface  102  to drive the catch  84  toward the latched position. The shape of the second portion  102 B of the cam surface  102  and its orientation relative to the pin  90  provides a mechanical advantage (e.g., about a 10:1 mechanical advantage in the illustrated embodiment, with other levels of mechanical advantage possible) that makes it easier for the actuator  228  to overcome the resistance of striker  52  to cinch the striker  52  tightly within the groove  94  of the catch  84 . 
     The controller  218  can be configured to direct the actuator  228  to operate to complete a predetermined number or rotations known to cause the driver  220  to drive the pawl  88  to the latched position before the controller  218  deactivates the actuator  228 . In other embodiments, a load sensor (e.g., electrical load sensor on the actuator  228 , strain gauge on any of mechanical power transmission components between the actuator  228  and the pawl  88 , an optical sensor, a switch sensor, and the like) can instead be coupled to the controller  218  to turn off the actuator  228  when the pawl  88  has reached the latched position. Once the striker  52  has been cinched and the catch  84  and the pawl  88  have reached their latched positions ( FIG. 8C ), the pawl  88  retains the catch  84  in the latched position, and the driver  220  can return to the neutral position ( FIG. 8D ). In the illustrated embodiment, the torsion spring  226  of  FIG. 7  is strong enough to return the driver  220  to the neutral position while the driver  220  is drivingly coupled with the actuator  228 , which requires back-driving the actuator  228 . In other embodiments, the actuator  228  and the driver  220  may be de-coupled (e.g., by a clutch) before the driver  220  is returned to the neutral position. 
       FIGS. 9A-9D  illustrate a power release sequence of the power latch assembly  200  of  FIG. 6 . Beginning at  FIG. 9A , the catch  84  and the pawl  88  are in their respective latched positions such that the roller  98  is in contact with the first portion  102 A of the cam surface  102 , and the striker  52  is retained securely by the catch  84 . In this state, the sensor-activating portion  216  of the pawl  88  is positioned remotely from the sensor  212 , and the driver  220  is in the neutral or “home” position. 
     Upon receiving a signal to release the latch  80 , the controller  218  (see  FIG. 6 ) sends a command signal to the actuator  228  to begin actuation. The signal received by the controller  218  may come from a sensor coupled with a door handle and responsive to movement of the door handle, or may come from a wireless device, or any other known device. In the illustrated embodiment, and as described in greater detail above, the actuator  228  is an electric motor that drives rotation of the pawl  88  through the gear train  236  and the driver  220 . As also discussed above, the illustrated gear train  236  includes the worm gear  240  that is engaged with the toothed portion  232  of the driver  220 . In the unlatching process of the illustrated embodiment, the actuator  228  moves the driver  220  in a clockwise direction so that the second protrusion  224 B of the driver  220  contacts and drives clockwise rotation of the pawl  88  to move the roller  98  from the first portion  102 A to the second portion  102 B of the cam surface  102 . Also in the illustrated embodiment, the actuator  228  rotates the pawl  88  an amount sufficient to pass over the center of the over-center spring  208 , at which time the spring  208  then biases the pawl  88  to the unlatched position of  FIG. 9C . In some embodiments, the catch  84  is moved to its unlatched position as the roller  98  contacts the surface  110  adjacent the cam surface  102 . When the pawl  88  of the illustrated embodiment reaches the unlatched position of  FIG. 9C , the portion  216  of the pawl  88  actuates the sensor  212 , which sends a signal to the controller  218  to indicate that unlatching is complete. The controller  218  can then stop the actuator  228 , and the driver  220  can be returned by the torsion spring  226  ( FIG. 7 ) to the neutral position as shown in  FIG. 9D . 
     Low friction between the roller  98  of the pawl  88  and the cam surface  102  of the catch  84  allows the illustrated power latch assembly  200  to be unlatched with significantly less actuation force on the pawl  88  as compared to conventional latches. The gear train  236  between the actuator  228  and the pawl  88  allows an even further reduction in the operational requirements of the actuator  228 , and allows the actuator  228  to be smaller, less expensive, and use less power to complete the unlatching operation. Because the operational forces on the pawl  88  can be so low, the pawl  88  need not be constructed of a particularly strong material, and can instead be made of an inexpensive and/or lightweight material such as plastic. It should also be noted that a single actuator (e.g., actuator  228  in the illustrated embodiment of  FIGS. 6-11B ) is operable for both power cinching operation and power release operations of the power latch assembly  200 , eliminating the need for multiple actuators. As described above, the actuator  228  in the illustrated embodiment is operated to move the pawl  88  during power cinching and power releasing, and the catch  84  is moved to its corresponding positions in either case by movement of the pawl  88 , since the catch  84  and the pawl  88  are configured for synchronous movement. 
       FIGS. 10A and 10B  illustrate a manual latching sequence of the power latch assembly  200  of  FIGS. 6-11B . This manual latching is carried out in the same manner as the above-described latching and power cinching sequence of  FIGS. 8A-8D , except that the actuator  228  is not operated for cinching, and as a result need not necessarily be present (along with the gear train  236  and driver  220 ) in alternate embodiments. As shown in  FIG. 10A , relative movement of the striker  52  against the catch  84  rotates the catch  84  clockwise. This rotation of the catch  84  causes corresponding rotation of the pawl  88  to an extent sufficient to cross over the center of the over-center spring  208  so that the spring  208  biases the pawl  88  to the latched position of  FIG. 10B . Once the pawl  88  has reached the latched position, movement of the catch  84  out of its latched position is blocked by the pawl  88 , whose roller  98  is in contact with the first portion  102 A of the cam surface  102 . In some embodiments, power cinching action of the power latch assembly  200  may be selectively controllable by the controller  218  so that the actuator  228  is only actuated for cinching under certain circumstances, or the power cinching feature can simply be deactivated for certain installations of the power latch assembly  200 . 
       FIGS. 11A and 11B  illustrate a manual release or unlatching sequence of the power latch assembly  200 . Although the actuator  228  is present and operable to release the striker  52  from the catch  84 , it may be desirable to provide an alternate element or device, or at least a back-up element or device, for effecting this release operation. Also, it should be noted that the actuator  228 , gear train  236 , and driver  220  need not necessarily be present to perform the manual release or unlatching sequence. Similar to the power release operation, a release force is applied directly to the pawl  88 , and the catch  84  is moved to its unlatched position in response to actuation by the pawl  88 . Although a particular manual actuator is not illustrated, any convenient element or device for inducing clockwise rotation of the pawl  88  can be provided. For example, a twistable knob can be directly or indirectly coupled to the pawl  88 , or a cable can be attached to the pawl  88  (e.g., at a distance from the pin  96 ) and can be operable in response to actuation of a handle, lever, or other element to be pulled and to exhibit a torque on the pawl  88  for moving the roller  98  off of the first portion  102 A of the cam surface  102 . With continued reference to  FIGS. 11   a  and  11   b , the pawl  88  can be further manually movable past the crossover point of the over-center spring  208  so that the spring  208  biases the pawl  88  to the unlatched position of  FIG. 11B . As described above, movement of the pawl  88  to the unlatched position causes corresponding movement of the catch  84  to its unlatched position so that the striker  52  is released from the groove  94 . 
       FIG. 12  illustrates another power latch assembly  300 . Except as described herein, the power latch assembly  300  of  FIG. 12  is structurally and functionally similar to the power latch assembly  200  of  FIGS. 6-11B  and thus, a duplicative description of the common features is not provided. Reference is hereby made to the description above in connection with  FIGS. 6-11B  for a more complete understanding of the features, elements, and operation (and possible alternatives to such features, elements, and operation) of the embodiment of  FIG. 12 . Common reference numbers are used where appropriate. 
     In the power latch assembly  300  of  FIG. 12 , the actuator  228  drives the worm gear  240  directly without other elements of the gear train  236  in the earlier-illustrated power latch assembly  200 . Although the absence of the torque-increasing gear train  236  can limit the maximum torque that can be applied to the pawl  88  in power cinching or power release operations (assuming the actuators  228  in the two power latch assemblies  200 ,  300  are equivalent in output), the power latch assembly  300  can be configured in some embodiments to operate without power cinching capability (e.g., in installations where this feature is not necessary or desired). By eliminating the power cinching feature, the maximum demand for torque on the pawl  88  can be reduced to that which is necessary for a power release operation. Because a power release operation only requires that the pawl  88  be rotated to roll the roller  98  off the first portion  102 A of the cam surface  102  and get over the crossover point of the over-center spring  208 , the gear train  236  can be eliminated in some applications. Removal of the gear train  236  allows overall reduction in the size and/or weight of the power latch assembly  300 , and although not shown, the housing  204  can be reduced in size to more closely follow the contour of the actuator  228 , which in the illustrated embodiment is oriented at an angle compared with the orientation of the actuator  228  in the power latch assembly  200  of  FIGS. 6-11B . Furthermore, where power cinching is not needed or desired, the driver  220  can be simplified by removing the first protrusion  224 A, and can be made smaller as a whole if desired. 
     As an alternate to removing the gear train  236  in the power latch assembly  300 , the gear train  236  from the power cinch-capable latch assembly  200  may be retained, in which case a smaller, lighter, and less powerful actuator may be used, and an overall reduction in size and weight may still be achieved. 
     Although the power latch assembly  300  of  FIG. 12  is described as having only a power release function and not a power cinching function, both power functions can be provided in other embodiments. However, in such cases, and depending at least in part upon the necessary force to perform cinching operations, the actuator  228  in the power latch assembly  300  may need to be more powerful than that of the power latch assembly  200 , and may not need to rely upon a torque increase from a gear train for power cinching. 
       FIGS. 13A and 13B  illustrate another power latch assembly  400  according to another embodiment of the present invention. The power latch assembly  400  of  FIGS. 13A and 13B  is structurally and functionally similar to the earlier-described power latch assemblies  200 ,  300  in many respects and thus, a duplicative description of the common features is not provided. Reference is hereby made to the description above in connection with  FIGS. 6-12  for a more complete understanding of the features, elements, and operation (and possible alternatives to such features, elements, and operation) of the embodiment of  FIGS. 13A and 13B . Common reference numbers are used where appropriate. 
     The power latch assembly  400  of  FIGS. 13A and 13B  includes a modified latch  80 ′ that is identical in most respects to the latch  80  of  FIG. 2 . Where the modified latch  80 ′ differs from the above-described latch  80  is that the pawl  88 ′ is modified to include an integral gear portion  432 . Interaction between the pawl  88 ′ and the catch  84  (i.e., the synchronous movement between latched and unlatched positions as described above) is the same as that between the pawl  88  and the catch  84  of  FIG. 2 , also shown and described as part of the latch assemblies  200 ,  300 . However, the use of a residual magnet actuator  428  allows (among other things) the elimination of the driver  220  present in the latch assemblies  200 ,  300 . 
     The residual magnet actuator  428  includes an output member, shown as a gear wheel  440  by way of example only. The illustrated gear wheel  440  is generally circular, and includes a plurality of teeth  444  that intermesh with a toothed portion  432  of the pawl  88 ′. Although it may not be required that the gear wheel  440  define a full circle covered with teeth  444 , the gear wheel  440  and the pawl  88 ′ are configured to be constantly engaged throughout the full range of motion of the pawl  88 ′ between the latched and unlatched positions. In other embodiments, driving force between the residual magnetic actuator  428  and the pawl  88 ′ can be accomplished by other suitable mechanical connections, such as by a linkage pivotably coupled at one end to an off-center location on the residual magnetic actuator, and pivotably coupled at an opposite end to an off-center location of the pawl  88 ′, or in still other manners. 
     With continued reference to the illustrated embodiment of  FIGS. 13A and 13B , when the latch assembly  400  is in the unlatched position, the portion  216  of the pawl  88 ′ actuates the switch  212 . The pawl  88 ′ is driven by the catch  84  out of the unlatched position to the latched position as the striker  52  is manually forced into the groove  94  of the catch  84 . As the pawl  88 ′ is driven counterclockwise to the latched position, the toothed portion  432  of the pawl  88 ′ drives the gear wheel  440  of the residual magnet actuator  428  clockwise. “Back-driving” the residual magnet actuator  428  during the latching operation allows energy to be stored in an energy storage device. The energy storage device can be a spring, such as a torsion spring internal to the residual magnet actuator  428 , a torsion spring coupled to the pawl  88 ′, an extension, compression, or other type of spring coupled to the residual magnet actuator  428  and/or to the pawl  88 ′, one or more elastic members coupled to the residual magnet actuator  428  and/or to the pawl  88 ′, and the like. The stored energy can be held by temporarily energizing the residual magnet actuator  428 , and can later be released to drive the latch  80 ′ to the unlatched state by temporarily energizing the residual magnet actuator  428  again. Energizing the residual magnet actuator  428  to hold the stored energy can be triggered by a controller in response to the sensor  212  sensing movement of the pawl  88 ′ to the latched position. The fundamentals of operation of the residual magnet actuator  428  are discussed in further detail below. 
       FIGS. 14 and 15  schematically illustrate operation of a residual magnet assembly  500 . The residual magnet includes at least two elements constructed of a material capable of retaining a magnetic flux when the elements are moved into contact with one another to provide a closed magnetic flux path. These elements ( 504 ,  508  in  FIGS. 14 and 15 ) can have any shape and size capable of performing this function. When current is applied to the electromagnet coil  512  as shown in  FIG. 14 , a loop-shaped magnetic flux path  516  is established through the elements  504 ,  508  of the assembly  500 , and as the vertical arrows  520  indicate, a magnetic attraction is established therebetween. After the electrical current is stopped as shown in  FIG. 15 , magnetic flux and the magnetic attraction between the elements  504 ,  508  are still present. To release the magnetic attraction between these elements  504 ,  508 , a reverse polarity current pulse is applied to the electromagnet coil  512  or the elements  504 ,  508  are moved away from one another sufficiently to break the closed magnetic flux path. If a reverse polarity current is not applied and if the closed magnetic flux path is not broken, the residual magnetic attraction will remain indefinitely. 
     There are many benefits of utilizing a residual magnet assembly such as that shown schematically in  FIGS. 14 and 15  and described above. The residual magnetic field remains internal to the assembly and does not emit a magnetic attraction to the surrounding environment. Furthermore, operation of a residual magnet is generally not affected by temperature, shock load, electromagnetic interference or external magnetic attack. A simple residual magnet can be used to inhibit various types of motion including separation (e.g., where two surfaces of the elements  504 ,  508  are pulled away from one another), translational or rotary movement (e.g., where the surfaces are shifted with respect to one another while still being kept facing and/or in contact with one another), and combinations of such movement. Residual magnets are also quiet and fast-operating, are easily scalable for various applications, are not susceptible to manual security attacks or power loss, and generally exhibit a simple design with low part count and minimal moving parts. A residual magnet assembly can also provide an inherent clutch slip feature that eliminates potential of component shear failure, provides constant torque resistance, and reduces system cost. 
     Further information regarding the residual magnet assemblies, the materials of such assemblies, and the manner of operation of such assemblies is found in U.S. Patent App. Pub. No. 20060219497, the entire contents of which are incorporated herein by reference insofar as they relate to residual magnets, residual magnetic devices and operation of such devices, and residual magnetic materials. 
       FIGS. 16-18  illustrate a toroidal residual magnet assembly  600  that functions similarly to the residual magnet  500  schematically illustrated in  FIGS. 14 and 15  and that is configured for use in the residual magnet actuator  428  of  FIGS. 13A and 13B . The toroidal residual magnet assembly  600  includes a core  605 , a coil  610 , and an armature  615 . The illustrated core  605  is generally circular, and includes a generally circular recess  620  between inner and outer pole faces  625 A,  625 B. The coil  610  is positioned within the recess  620  in the core  605 , and the armature  615  is positioned over the coil  610  so that the armature  615  rests against the pole faces  625 A,  625 B. Energizing the coil  610  (i.e., flowing electrical current therethrough as shown in  FIG. 17 ) creates magnetic saturation of the assembly. A loop-shaped magnetic flux path is established around the coil  610  at each cross-sectional location, as shown by the magnetic field direction arrows  630  in  FIG. 17 . As the vertical arrows  635  indicate, a magnetic attraction is established between the core  605  and the armature  615  in a direction parallel to the axis A 6  (see  FIG. 16 ) of the toroidal residual magnet  600 . After electrical current to the coil  610  is stopped as shown in  FIG. 18 , residual magnetic flux causes the magnetic attraction between the core  605  and the armature  615  to remain. As shown by the field of arrows  640  in  FIG. 18 , the magnetic attraction can create a generally uniform pressure distribution across the armature  615  and the pole faces  625 A,  625 B of the core  605 . To release the magnetic attraction between the core  605  and the armature  615 , a reverse polarity current pulse is applied to the coil  610 , or the armature  615  is physically separated from the core  605 . Response time for release by a reverse polarity current is very fast (e.g., about 25 milliseconds). The residual magnet  600  and the corresponding actuator  428  allow not only fast operation, but also very quiet operation as gear and motor noises can be eliminated. 
     The toroidal residual magnet  600  of  FIGS. 16-18  allow movement-inhibiting holding power between the core  605  and the armature  615  to be generated with low electrical power consumption, and to then be maintained via the residual magnetic attraction with no power consumption thereafter. In some embodiments, the magnetic attraction can create a pressure distribution of at least about 0.84 N/mm 2  between the armature  615  and core  605 . The residual magnetic attraction resists axial pulling apart of the core  605  and the armature  615 , and can also resists twisting of one of the core  605  and the armature  615  relative to the other about the axis A 6 . When used as a residual magnet actuator  428  of  FIGS. 13A and 13B , the armature  615  or the core  605  can be coupled to or made integral with the illustrated gear wheel  440 . Rotation of the gear wheel  440  with the associated residual magnetic element (e.g., armature  615  or core  605 ) relative to the other residual magnetic element is allowed freely when the magnetic flux is not present, and is inhibited or prevented when the magnetic flux is present. This allows the gear wheel  440  to be driven by the pawl  88 ′ during the latching operation to store potential energy (e.g., in a torsion spring as described above), and then to be locked in place by the magnetic attraction generated by a temporary pulse of electrical current. To effect unlatching and release of the striker  52  from the catch  84 , the magnetic flux in the residual magnet  600  of the illustrated embodiment of  FIGS. 13A and 13B  is canceled by a temporary pulse of electrical current having opposite polarity as the magnetic flux-inducing first pulse. When the magnetic flux is thereby canceled, the potential energy is released to move the gear wheel  440  and drive the pawl  88 ′ and the catch  84  to their respective unlatched positions. 
       FIG. 19  illustrates a manual latch assembly  700  including the latch  80  of  FIG. 2 . Except as described herein, the manual latch assembly  700  of  FIG. 19  is structurally and functionally similar to the power latch assemblies  200 ,  300 ,  400  of  FIGS. 6-13B  and thus, a duplicative description of the common features is not provided. Reference is hereby made to the description above in connection with  FIGS. 6-13B  for a more complete understanding of the features, elements, and operation (and possible alternatives to such features, elements, and operation) of the embodiment of  FIG. 19 . Common reference numbers are used where appropriate. 
     In the embodiment of  FIG. 19 , a manual release actuator  710  is coupled to the pawl  88  at a distance from the pin  96  on which the pawl  88  is rotatably mounted. In the illustrated embodiment, the manual release actuator  710  is a Bowden cable that can be pulled from an end remote from the pawl  88  to rotate the pawl  88  out of the latched position ( FIG. 19 ) toward the unlatched position. From the latched position, pulling the manual release actuator  710  generates a torque on the pawl  88 , which rotates clockwise about the pin  96 . The torque is sufficient to overcome the bias of the over-center spring  208  and to move the roller  98  from the first portion  102 A to the second portion  102 B of the cam surface  102 . Upon further pulling of the manual release actuator  710 , the crossover point of the over-center spring  208  is crossed, and the spring  208  then biases the pawl  88  to the unlatched position. Movement of the pawl  88  to the unlatched position causes a corresponding movement (i.e., counterclockwise rotation about pin  90 ) of the catch  84  to its unlatched position since the catch  84  and the pawl  88  are configured for synchronous movement as described above. Once unlatched, the manual release actuator  710  can be released, and the latch  80  will be held in the unlatched state by the over-center spring  208 . Latching can occur manually by action of the striker  52  on the catch  84 , and with the aid of the over-center spring  208 , as described above. While the above-described power latch assemblies  200 ,  300 ,  400  illustrate many features and benefits of the latch  80 , the manual latch assembly  700  of  FIG. 19  illustrates that the usefulness of the latch  80  is not limited to such power latch assemblies. 
       FIGS. 20A and 20B  illustrate another latch  880  that is similar in many respects to the latch  80  of  FIG. 2 . The latch  880  is illustrated in a closed latched state in  FIG. 20A  and an open unlatched state in  FIG. 20B . The latch  880  includes a catch  884  rotatable about a first axis A 3 , and a pawl or reaction plate  888  rotatable about a second axis B 3  that can be parallel to the first axis A 3 . The catch  884  and the pawl  888  are co-drivable. The illustrated catch  884  includes a hook portion  844  that engages a striker  852  in the latched position. Also, the illustrated pawl  888  includes a cam roller  898  that is engageable with a concentric cam surface  802  of the catch  884  (i.e., concentric with respect to the axis of rotation B 3  of the pawl  888 ). With the latch  880  in the latched state of  FIG. 20A , the load applied to the cam roller  898  from the cam surface  802  from any force on the catch  884  in the unlatching direction is generally directed toward the axis B 3 . Thus, similar to the latch  80  of  FIG. 2 , the pawl  888  is stable, since there are no or very low rotational loads on the pawl  888  to drive it toward the unlatched state. Accordingly, the latch  880  must be released to the latched position (i.e., to release the striker  854  from the hook  844 ) by applying an external force or torque to the pawl  888  so that the pawl  888  rotates the roller  898  off the concentric cam surface  802 . 
     To release the latch  880  from the latched state of  FIG. 20A , the pawl  888  is rotated clockwise about the axis B 3  so that the cam roller  898  is removed from the concentric cam surface  802 . The catch  884  need not be actuated directly by any outside force or actuator. The external force on the pawl  888  to drive the latch  880  to the unlatched state can be provided by any type of actuator (e.g., a mechanical lever, a spring load, a DC motor, a solenoid, a smart material actuator, etc.). To close the latch  880 , the pawl  888  is rotated counterclockwise about the axis B 3 . The rotation of the pawl  888  may be effected by an actuator, or merely by contact from the striker  852  when the striker  852  is swung into contact with the pawl  888 . Movement of the pawl  888  to the latched position drives synchronous movement of the catch  884  to its latched position by way of the cam roller  898  which drives rotation of the catch  884 . 
     The unique engagement between the roller  898  of the pawl  888  and the concentric cam surface  802  of the catch  884  enables the pawl  888  to securely hold the catch  884  in the latched position while also allowing the pawl  888  to be moved to release the catch  884  as desired with the application of only a small force due to the low friction contact. The latch  880  of  FIGS. 20A and 20B  may be substituted for the latch  80  in one or all of the latch assemblies  200 ,  300 ,  400 ,  700  shown in the drawings and described above. 
       FIGS. 21-23  illustrate yet another latch  980 . The latch  980  is similar in many structural and functional aspects to the latch  80 , and may be substituted into one or all of the latch assemblies  200 ,  300 ,  400 ,  700  shown in the drawings and described above. Where appropriate, reference numbers for the latch  980  are similar to those of the latch  80 , incremented by  900 . Reference is hereby made to the above description, and the accompanying drawings, for similar characteristics such that the description below is focused primarily on the additional features of the latch  980  illustrated in  FIGS. 21-23 . 
     As described with reference to the other latches above, the latch  980  includes a catch  984  and a pawl  988  that are co-drivable. The pawl  988  selectively secures or retains the catch  984  in a latched position ( FIG. 23 ) in which a striker  952  may be held fixed by the catch  984 . Rotation of the catch  984  from the unlatched position ( FIG. 21 ) to the latched position ( FIG. 23 ), counterclockwise in the drawings about pin  990  and axis A 4 , corresponds to rotation of the pawl  988  from an unlatched position to a latched position, clockwise in the drawings about pin  996  and axis B 4 . In some constructions, a roller  998  of the pawl  988  may move along the cam surface  1002  of the catch  984  during rotation of the catch  984  to the latched position. In some constructions, the pawl  988  may be configured to provide a driving force, alone or in combination with a force applied by the striker  952 , to move the catch  984  to the latched position. A first portion  1002 A of the cam surface  1002  has a curvature substantially concentric with the pawl axis B 4  when the catch  984  is in the latched position. A second portion  1002 B of the cam surface  1002  is non-concentric with the pawl axis B 4  when the catch  984  is in the latched position, and rather, is shaped so that the pawl  988  may exert a cinching or closing force on the catch  984  as the pawl  988  rotates from the transition position of  FIG. 22  to the latched position of  FIG. 23 . 
     In order to inhibit the catch  984  from over-rotating in the latching direction, and to ensure that the roller  998  of the pawl  988  remains in contact with the first or “concentric” cam surface portion  1002 A, the catch  984  and the pawl  988  are provided with a first set of interference structures. In the illustrated construction, a projection  1009 A is formed on the catch  984  and is configured to abut a surface  1009 B of the pawl  988  if the catch  984  is rotated (further counterclockwise as viewed in the drawings) past the latched position of  FIG. 23 . 
     To release the latch  980 , the pawl  988  is rotated about the pawl axis B 4  (counterclockwise in the drawings) so that the pawl roller  998  moves off of the first cam surface portion  1002 A to the second cam surface portion  1002 B of the catch  984 . From this point, the pawl  988  does not resist movement of the catch  984  to the unlatched position of  FIG. 21 , and may assist in driving the catch  984  to the unlatched position. For example, the pawl  988 , and particularly the pawl roller  998  in the illustrated construction, may contact a surface  1010  of the catch  984  that is adjacent the cam surface  1002  to apply a force to the catch  984  in the unlatching direction. The unlatching force may be present on the pawl  988  by a powered actuator or by a passive energy-storage device, such as a spring. 
     When the catch  984  and the pawl  988  reach the unlatched positions of  FIG. 21 , the pawl  988  is removed from contact with the surfaces ( 1002 ,  1010 ) that make up the pawl-receiving recess or groove  1006 . However, in the illustrated construction, another separate physical interface is established between the catch  984  and the pawl  988  in the form of a projection  1013 A on the catch  984  and a corresponding recess or groove  1013 B of the pawl  988 . It should be appreciated that the male/female configuration and the type of structures making up the interface are not necessarily limiting and may be varied in alternate constructions. The interface between the catch  984  and the pawl  988  formed by the projection  1013 A and the groove  1013 B may be used wholly or in combination with other limiting structures to control the orientation of the catch  984  and/or the pawl  988  when unlatched. However, the interface further enables a driving engagement between the catch  984  and the pawl  988 . Thus, when the catch  984  is rotated from the unlatched position of  FIG. 21  toward the latched position by contact with the striker  952 , the rotation of the catch  984  about the axis A 4  drives corresponding rotation of the pawl  988  about the pawl axis B 4  toward its latched position. After a predetermined range of travel with the catch  984  driving the pawl  988 , the pawl  988  is received back into the groove  1006  of the catch  984 , and ultimately the roller  998  re-engages the cam surface  1002  for driving the catch  984  to the latched position. 
     As described above with reference to other latch assembly constructions, energy applied during a latching event may be stored as the pawl  988  is driven from the unlatched position to the latched position. The energy stored may later be released upon the pawl  988  to release the pawl  988  and the catch  984  to their respective unlatched positions. Although the pawl  988  is stable in its latched position ( FIG. 23 ) and resistant to being backward-driven by the catch  984 , the release energy required to release the pawl  988  from the latched position is very low as the roller  998  must simply be moved off of the concentric cam surface  1002 A. 
     The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention. For example, in each of the illustrated embodiments described and illustrated herein, a roller  98 ,  898 ,  998  is carried by the pawl  88 ,  888 ,  988  and contacts various surfaces of the catch  84 ,  884 ,  984  including cam surfaces  102 ,  110 ,  802 ,  1002 ,  1010 . Although the rolling and camming contact is highly desirable to reduce friction between the pawl  88 ,  888 ,  988  and the catch  84 ,  884 ,  984 , in some embodiments the roller  98 ,  898 ,  998  can be eliminated to simplify construction and assembly of the latch while still permitting proper functioning of the latch. In such embodiments, other manners of reducing friction between the pawl  88 ,  888 ,  988  and the catch  84 ,  884 ,  984  can instead be utilized, such as by constructing part or all of the pawl  88 ,  888 ,  988  and/or the catch  84 ,  884 ,  984  from low-friction material, or by incorporating one or more low-friction elements at the interface between the pawl  88 ,  888 ,  988  and the catch  84 ,  884 ,  984  (e.g., separate elements attached to the pawl  88 ,  888 ,  988  or the catch  84 ,  884 ,  984 ). 
     Furthermore, it will be appreciated by one having ordinary skill in the art that the configuration of the camming components may be reversed while maintaining the operational characteristics described above. For example, the pawl  88 ,  888 ,  988  may be formed with cam surfaces (e.g., convexly shaped cam surfaces complementary to the illustrated cam surfaces  102 ,  110 ,  802 ,  1002 ,  1010 ) and the catch  84 ,  884 ,  984  may be provided with a follower structure (e.g., a roller similar to pawl roller  98 ,  898 ,  998 ) movable along such cam surfaces.