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REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of PCT Application No. PCT/GB2008/000328 filed Jan. 31, 2008, which claims priority to United Kingdom Application No. GB 0703597.5 filed Feb. 23, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to latch assemblies, and in particular latch assemblies for use with car doors and car boots. 
         [0003]    Latch assemblies are known to releasably secure car doors in a closed position. Operation of an inside door handle or an outside door handle would release the latch, allowing the door to open. Subsequent closure of the door will automatically relatch the latch. Electric actuators are commonly employed in car latches in order to release them. Known latches incorporate a rotatable claw which engages with a striker mounted on an opposing surface (for example, a car door frame) in order to retain the door in a closed position. This rotating claw is often held in position by a pawl, which is also often a rotating component. Release of the claw is thereby achieved by rotating the pawl from an engaged position, whereby it engages and retains the claw, to a disengaged position, whereby the claw is free to rotate. Movement of the pawl is often undertaken by electric actuators. It is desirable to reduce the amount of force required to move the pawl from an engaged position to a disengaged position such that the size of the electric actuator can be reduced, thereby reducing weight and part cost. 
         [0004]    Simple known latch assemblies include a pawl that is mounted to rotate about a single axis. Such pawls are rotatably mounted on a substantially cylindrical pawl pivot pin inserted into a circular pawl pin orifice in the pawl. The pawl pivot pin is fixed to a stationary latch chassis. The pawl pivot pin has to be of a certain radius in order to withstand loads that the latch may undergo during normal operation and also during high load impact events. 
         [0005]    A problem with this type of known latch is that a radius of the pawl pivot pin, which as described must be of a certain magnitude to withstand loads, is directly related to the size of the contact area between the pawl and said pawl pivot pin. This is problematic as the amount of friction between these two components is influenced by the amount of dust and contaminants that may accrue between them. Therefore, as the contact surface area is increased, the levels of friction inherent within the latch in use is also increased, and a greater actuation force is required to overcome such friction. Therefore, larger and more expensive actuators are required which is undesirable. 
         [0006]    GB2409706 shows an example of a low energy release latch  100  (as shown in  FIG. 1 ) including a first pawl  140  pivotally attached to a toggle link  130 , and also to a second pawl  160  configured to retain the toggle link  130 . A high level of force acts on the first pawl  140  as a result of the vehicle door seal load, driving the claw  120  in a clockwise direction. The seal load acts to collapse the toggle link and pawl arrangement as shown in  FIG. 8 , which is prevented in  FIG. 1  by the interaction of the first pawl  140  and the second pawl  160 . Release of the low energy release latch  100  is therefore achieved by a clockwise rotation of the second pawl  160 , which in turn releases the first pawl  140 . 
         [0007]    WO/2006/087578 discloses a device (see  FIG. 1 ), in which the first pawl  16  is mounted on a crankshaft  50 . Door seal loads act to rotate the rotating claw  14  in a clockwise direction, which rotation is prevented by the first pawl  16 . The first pawl  16  is mounted on a crankshaft  18  and is configured such that force FP acts to generate a clockwise torque on the crankshaft  18 , which is rotatationally constrained by a release plate  72  acting on a release lever  52  (see  FIG. 1B ). Release by actuation of the release plate  72  allows the crankshaft  50  to rotate and the pawl to move under force FP to enable the latch to open. 
         [0008]    It can be clearly seen in WO/2006/087578 that the radius on which the first pawl  16  rotates about a crank pin  54  is necessarily large in order to encompass a cylindrical pin  56  (see  FIG. 1C ). The radius of the crank pin  54  therefore has to be equal to at least the distance between the crank pin axis Y and the crank shaft axis A plus the radius of the cylindrical pin  56  (i.e., the minimum required radius r min ). 
         [0009]    Such a large radius of rotation means that a perimeter of a pivot hole  46  is significant. Typically, the radius of the pivot hole  46  is in the order of 9 millimeters or more. This is problematic as dust contamination can cause excessive friction between the first pawl  16  and the crankshaft  50 , increasing the effort required to rotate them relative to each other. This is undesirable as larger actuators are required to rotate the two components relative to each other. 
         [0010]    Any attempt to reduce the radius of the crankshaft  50  to distances below the minimum required radius r min  would result in significant weakening of the crankshaft and consequently likely failure of this component. 
         [0011]    Referring to FIG. 1 of WO/2006/087578, a torque is applied to an eccentric  54  as the line of action of force FP is offset from an axis A. The size of the lever arm at which this torque is applied is determined by the start angle of the eccentric  54  (i.e., in the closed position). By way of explaining what is meant by “start angle”, at start angles of 0 and 180 degrees, the eccentric  54  is at top dead center (unstable equilibrium) and bottom dead center (stable equilibrium), respectively. As the angle tends towards 90 degrees, the lever arm increases to a maximum, and the maximum torque for a given force FP is applied to the eccentric. 
         [0012]    As the start angle decreases, the lever arm producing the torque on the eccentric  54  decreases. As such, if the angle is too low (i.e., below a minimum backdrive angle), the torque produced by the lever arm and the force FP will be insufficient to overcome the friction in the system, rotate the eccentric  54 , and open the latch. In known latch arrangements, the start angle must be above the minimum backdrive angle, typically in the order of 54 degrees. 
         [0013]    This minimum backdrive angle is indicative of the friction inherent in the latch assembly and therefore of the torque required to open the latch assembly. If it is reduced, a lower torque is sufficient to open the latch. This is beneficial as less effort is therefore required to release and latch the latch. 
       SUMMARY OF THE INVENTION 
       [0014]    It is an object of the present invention to provide a lower energy release latch by overcoming the above disadvantages. 
         [0015]    According to a first aspect of the present invention, there is provided a latch assembly having a chassis, a latch bolt movably mounted on the chassis and having a closed position for retaining a striker and an open position for releasing the striker, and a pawl having an engaged position at which the pawl is engaged with the latch bolt to hold the latch bolt in the closed position and a disengaged position at which the pawl is disengaged from the latch bolt, thereby allowing the latch bolt to move to the open position. The pawl is rotatably mounted via a pawl pivot pin about a pawl axis, and the pawl pivot pin includes a first arcuate portion having a first radius about the pawl axis. A cross-sectional area of the pawl pivot pin, taken perpendicular to the pawl axis, is greater than an area of a circle having the first radius. 
         [0016]    By having a pawl pivot pin cross sectional area substantially greater than the area of the circle having the radius of the first arcuate portion, it is possible to have a first arcuate portion of relatively small radius without compromising the strength of the pawl pivot pin. This lower radius of the first arcuate portion means that the detrimental effect of dust and contaminants is reduced, as the mating area between the pawl pivot pin and the surface against which it rotates is reduced. This also reduces the minimum backdrive angle compared to known latches. 
         [0017]    In one example, the pawl pivot pin is mounted in a pawl pin orifice including a second arcuate portion having a second radius about the pawl axis, substantially similar to the first radius, and in which a cross-sectional area of the pawl pin orifice, taken perpendicular to the pawl axis, is greater than a area of a circle having the second radius. 
         [0018]    The arrangement may use a “live” pivot (i.e., in which the pawl pivot pin is connected to the pawl and the pawl pin orifice is defined in an adjacent component, e.g., the chassis or an eccentric) or a “dead” pivot (in which the pawl pivot pin is connected to the chassis or the eccentric and the pawl pin orifice is defined in the pawl). 
         [0019]    According to a second aspect of the present invention, there is provided a latch assembly having a chassis, a latch bolt movably mounted on the chassis and having a closed position for retaining a striker and an open position for releasing the striker, and a pawl having an engaged position at which the pawl is engaged with the latch bolt to hold the latch bolt in the closed position and a disengaged position at which the pawl is disengaged from the latch bolt, thereby allowing the latch bolt to move to the open position. The pawl is rotatably mounted via a pawl pivot pin about a pawl axis, and the pawl pivot pin is rotatably mounted in a pawl pin orifice including a pawl pin orifice arcuate portion having a second radius about the pawl axis. A cross-sectional area of the pawl pin orifice, taken perpendicular to the pawl axis, is greater than an area of a circle having the second radius. 
         [0020]    By making the cross sectional area of the pawl pin orifice greater than that of a circle having the radius of the second arcuate portion, it is ensured that less than an entire perimeter of the pawl pivot pin is in contact with the pawl pin orifice. Therefore, the contact area between the pawl pivot pin and the pawl pin orifice is reduced compared to known arrangements, and as such, the effect of dust and contaminants is reduced. Furthermore, the fact that the area of the pawl pin orifice is significantly larger than the area of the pawl pivot pin leaves a gap from which dust and contaminants can escape and be ejected from the mechanism. In this manner, the amount of friction in the latch is reduced, and consequently, the size of the actuators may also be reduced. Furthermore, the likelihood of the latch becoming stuck or jammed because of friction arising from dust or contaminants is also reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  is a backplate side view of certain components of a first embodiment of a latch assembly according to the present invention in a closed position; 
           [0023]      FIG. 1A  is a backplate side view of a pawl of  FIG. 1 ; 
           [0024]      FIG. 1B  is a latch plate side view of the pawl of  FIG. 1 ; 
           [0025]      FIG. 2  is a backplate side view of the latch assembly of  FIG. 1  in a released position; 
           [0026]      FIG. 3A  is a backplate side view of the latch assembly of  FIG. 1  in a semi closed position; 
           [0027]      FIG. 3B  is a backplate side view of the latch assembly of  FIG. 1  in a position between the semi closed position of  FIG. 3A  and a first safety position; 
           [0028]      FIG. 3C  is a backplate side view of the latch assembly of  FIG. 1  in a semi-closed position between the first safety position and the closed position; 
           [0029]      FIG. 3D  is a backplate side view of the latch assembly of  FIG. 1  in a fully closed position; 
           [0030]      FIG. 4A  is a schematic view of a prior art latch; 
           [0031]      FIG. 4B  is a detailed view of the latch assembly of  FIG. 1 ; 
           [0032]      FIG. 5  is a backplate side view of certain components of a second embodiment of a latch assembly according to the present invention in a closed position; 
           [0033]      FIG. 6  is a retention plate side view of the latch of  FIG. 5  in a closed position; 
           [0034]      FIG. 7A  is a retention plate side view of the latch assembly of  FIG. 5  in a released position; 
           [0035]      FIG. 7B  is a backplate side view with the latch assembly of  FIG. 5  in a released position; 
           [0036]      FIG. 8  is a backplate side view of the latch assembly of  FIG. 5  in an open position; 
           [0037]      FIG. 9A  is a backplate view of the latch assembly of  FIG. 5  in a semi closed position; 
           [0038]      FIG. 9B  is a backplate view of the latch assembly of  FIG. 5  in a first safety position; 
           [0039]      FIG. 9C  is a backplate view of the latch assembly of  FIG. 5  in a semi closed position between the first safety position and the closed position; 
           [0040]      FIG. 9D  is a backplate side view of the latch assembly of  FIG. 5  in a fully closed position; 
           [0041]      FIG. 10  is a backplate side view of certain components of a third embodiment of a latch assembly according to the present invention; 
           [0042]      FIG. 11  is a retention plate side view of the latch assembly of  FIG. 10 ; 
           [0043]      FIG. 12  is a backplate side view of certain components of a fourth embodiment of a latch assembly according to the present invention in a closed position; 
           [0044]      FIG. 13  is a backplate side view of the latch assembly of  FIG. 12  in a released position; 
           [0045]      FIG. 14A  is a backplate side view of certain components of a fifth embodiment of a latch assembly according to the present invention in a closed position; 
           [0046]      FIG. 14B  is a retention plate side view of the latch assembly of  FIG. 14A  in a closed position; 
           [0047]      FIG. 14C  is an exploded view of certain components of a sixth embodiment of a latch assembly according to the present invention; 
           [0048]      FIG. 15A  is a backplate side view of certain components of a seventh embodiment of a latch assembly according to the present invention in an open position; and 
           [0049]      FIG. 15B  is a retention plate side view of the latch assembly of  FIG. 15A  in an open position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0050]    With reference to  FIG. 1 , there is shown a latch assembly  10  including a latch chassis  12 , a latch bolt in the form of a rotating claw  14 , a pawl  16 , and a pawl pivot pin  18 . The latch assembly  10  is mounted on a door  8  (only shown in  FIG. 1 ). 
         [0051]    The major components of the latch chassis  12  are a retention plate  20  and a backplate  23  (only shown partially in  FIG. 1 ). The backplate  23  is mounted on an opposite side of the latch assembly  10  such that views from a backplate side are in an opposite direction to views from a retention plate side of the latch assembly  10 . The retention plate  20  is generally planar and includes a mouth  22  for receiving a striker  24 , generally attached to a door frame (not shown). Projecting from the retention plate  20  is a claw pivot pin  26 , a pawl pivot pin  28  and a stop pin  30 . The pawl pivot pin  18  includes a cylindrical body  52  and a lug  54  generally offset from the cylindrical body  52  and including a first arcuate portion  56  of a radius A. In this case, the pawl pivot pin  18  is non-rotatably fixed to the latch chassis  12 . 
         [0052]    The retention plate  20  further includes a mouth  34  for receiving the striker  24 . Furthermore, the retention plate  20  further includes threaded holes  36  which in use are used to secure the latch assembly  10  to the door  8 . 
         [0053]    The rotating claw  14  is mounted rotatably about the claw pivot pin  26  and includes a mouth  32  for receiving the striker  24 . The rotating claw  14  further includes a first safety abutment  38  and a closed abutment  40 . 
         [0054]    The pawl  16  is generally planar and includes a claw abutment  46  and a chassis abutment  48 . The pawl  16  further includes a pawl pivot pin orifice  50 . The pawl pivot pin orifice  50  includes a second arcuate portion  58  of a radius B and a third arcuate portion  60  of radius C. Referring to  FIGS. 1A and 1B , these arcuate portions  56 ,  58  and  60  and their radii can be seen in more detail. It will be appreciated that all three arcuate portions  56 ,  58  and  60  have a substantially common origin, that is, a pawl axis X about which the pawl  16  rotates. It should also be noted that the radius A and the radius B are substantially similar such that the pawl  16  can rotate relative to the pawl pivot pin  18  about the pawl axis X. 
         [0055]    There is also provided an actuator  62  (shown schematically) connected to an actuator rod  64 , which is in turn connected to the pawl  16 . Actuation of the actuator  62  retracts the actuator rod  64  such that the pawl  16  rotates in a clockwise direction against the bias of a spring  66 . 
         [0056]      FIG. 2  shows the latch assembly  10  in a released position whereby the actuator  62  has rotated the pawl  16  in a clockwise fashion in order to allow the rotating claw  14  to rotate in a clockwise fashion about the pawl axis X of the claw pivot pin  26 . As can be seen, this rotation allows the striker  24  to be released from the latch assembly  10  (the position of the pawl  16  in the closed position is shown in dotted line for comparison). 
         [0057]    The pawl  16  returns to a rest position after the closed abutment  40  of the rotating claw  14  has rotated past the claw abutment  46  of the pawl  16 . In this case, the rest position is as shown in the dotted line i.e., it is the same as the closed position. The return to the closed position is aided by the spring  66 . Alternatively or additionally, the actuator  62  could act in a reverse direction in order to allow the pawl  16  to return to its rest position. 
         [0058]      FIGS. 3A to 3D  show the latch assembly  10  moving from the released state shown in  FIG. 2  to the closed state shown in  FIGS. 1 and 3D . Closure of the latch assembly  10  is enabled by movement of the striker  24  relative to the latch assembly  10  from the right to the left when viewing  FIGS. 3A to 3D . This corresponds to a closing of the door  8 . As can be seen in  FIG. 3A , the movement of the striker  24  tends to rotate the rotating claw  14  in a counter-clockwise direction. This in turn rotates the pawl  16  in a clockwise direction from the rest position of  FIG. 2  against the bias of the spring  66  until the first safety abutment  38  has passed the claw abutment  46  of the pawl  16 . In the position shown in  FIG. 3B , the latch assembly  10  is approaching a first safety condition whereby the first safety abutment  38  is about to engage the claw abutment  46 . 
         [0059]    As the striker  24  moves further to the left in  FIG. 3C , the pawl  16  begins again to rotate in a clockwise sense against the bias of the spring  66  until the rotating claw  14  reaches a closed position as shown in  FIG. 3D  and the bias of the spring  66  returns the pawl  16  to the closed position whereby the claw abutment  46  is engaged with the closed abutment  40  of the rotating claw  14 . The chassis abutment  48  of the pawl  16  engages with the stop pin  30  such that the pawl  16  cannot rotate any further. The latch assembly  10  is now back in the closed condition, as shown in  FIG. 1 . 
         [0060]    Comparing  FIGS. 4A and 4B ,  FIG. 4A  shows a schematic view of a method of mounting a pawl  17  to a latch chassis via a pawl pivot pin  19  of a radius D. The radius D of the pawl pivot pin  19  needs to be sufficient to withstand the forces transmitted through the latch both in normal use and in high load events, for example, vehicle crash events. It will be appreciated that as the radius D is increased, the effective contact area between the pawl pivot pin and the pawl  17  is increased. The resulting increase in contact area between these two components means that a higher amount of dust and contaminants are able to infiltrate the contact area during the service life of the latch, resulting in the requirement for a higher force required to rotate the pawl  17  in a clockwise sense in order to release the latch. Therefore, the actuator  63  has to be of sufficient size to overcome these frictional forces. 
         [0061]    Referring now to  FIG. 4B , the radius of contact between the pawl pivot pin  18  and the pawl  16  is defined by the radius A of the first arcuate portion  56  of the pawl pivot pin  18 . Furthermore, the geometry of the pawl pivot pin orifice  50  is such that only a segment of the circle defined by radius A of the first arcuate portion  56  is in contact between the pawl pivot pin  18  and the pawl  16 . Therefore, the contact area, and consequently the effect of the ingress of dust and contaminants, is significantly reduced, reducing the load required to rotate the pawl  16  and therefore the size of the actuator  62 . 
         [0062]    It will also be noted that if the radius D of a known pawl pivot pin  19  was simply reduced, then the required strength would not be achieved in order to resist the loading requirements of the latch assembly  9 . The present invention overcomes this problem by providing a pawl pivot pin  18  of significant size with the cylindrical body  52  and the lug  54  on which the first arcuate portion  56  is defined. Therefore, the pawl pivot pin  18  is able to resist the required loading, while also reducing the frictional forces between the pawl pivot pin  18  and the pawl  16 . 
         [0063]      FIG. 5  shows a second embodiment of a latch assembly  110 . The latch assembly  110  is similar to the latch assembly  10  with common components having reference numerals of the latch assembly  10 , but 100 greater. 
         [0064]    The latch assembly  110  includes a pawl  116  substantially identical to the pawl  16  of the latch assembly  10 . However, a pawl pivot pin  168  differs from the pawl pivot pin  18  in that it is rotatably mounted on a latch chassis  112  such that it is able to rotate about a pivot axis Y (as mentioned above, the pawl pivot pin  18  is non-rotatably fixed to the latch chassis  12 ). Referring to  FIG. 6 , this rotation is brought about by a cylindrical portion  170  (an extension of a cylindrical body  152 ) of the pawl pivot pin  168 , which passes through a retention plate  120 . It will therefore be appreciated that the pawl pivot pin  168  forms an eccentric as the pawl axis X and the pivot axis Y are offset. 
         [0065]    As shown in  FIG. 6 , a lever  172  is connected to the cylindrical portion  170  of the pawl pivot pin  168  on a side of the retention plate  120  opposite to the pawl  116 . The lever  172  is held in position by a moveable abutment  174  which is configured to be displaced in a downwardly direction by an actuator  176 . The lever  172  is prevented from moving clockwise when viewing  FIG. 6  by a lever abutment  178 . 
         [0066]    In the closed position as shown in  FIG. 5 , the seal loads between the door and the vehicle frame result in a striker  124  exerting a force F on a mouth  132  of a claw  114 . This in turn results in a force being applied by a closed abutment  140  of the claw  114  onto a claw abutment  146  of the pawl  116 . This force is denoted by G in  FIG. 5 . It should be noted that the force G does not pass through the pivot axis Y, and as such the torque is applied to the pawl pivot pin  168  in a clockwise fashion with respect to  FIG. 5 . This results in a counter-clockwise torque when viewing  FIG. 6  on the pawl pivot pin  168  and consequently the lever  172 . This motion is inhibited by the presence of the moveable abutment  174 , and as such, the latch assembly  110  remains in a closed position. In order to open the latch assembly  110 , the actuator  176  is actuated such that the moveable abutment  174  moves out of contact with the lever  172 , as shown in  FIG. 7A . Therefore, under the action of force G, the lever  172  rotates in a counter-clockwise fashion as shown in  FIG. 7A , which is equivalent to a rotation in a clockwise sense of the pawl pivot pin  168  when viewing  FIG. 7B . This motion can be seen by comparing the position of the pawl axis X in  FIGS. 5 and 7B   
         [0067]    The resulting motion of the pawl  116  moves the claw abutment  146  out of engagement with the closed abutment  140 , thus allowing the claw  114  to rotate in a clockwise sense and release the striker  124 . 
         [0068]    As can be seen in  FIG. 8 , the latch assembly  110  is in an open condition with the claw  114  rotated such that the striker (not shown) is released. The lever  172  has returned to its original position against the lever abutment  178 . The mechanism by which the lever  172  returns to its original position is by way of a reset abutment on the claw  114  (not shown), which rotates the pawl pivot pin  168  back to its original position as shown in  FIG. 5 . A more detailed explanation of the reset sequence may be found below (with respect to  FIGS. 15A and 15B ). 
         [0069]    The moveable abutment  174  has also been returned to its original position in order to constrain the lever  172 . It will be noted that pawl axis X is in the same position in  FIGS. 5 and 8 . 
         [0070]    As there is no force G acting on the pawl  116 , the pawl  116  is kept in position via the bias of a spring  166  holding a chassis abutment  148  against a stop pin  130 . It will be noted that during release of the latch assembly  110 , the chassis abutment  148  and the stop pin  130  are in constant contact, and in fact, the pawl  116  is able to rotate about the contact point between these two components. 
         [0071]    Referring to  FIGS. 9A to 9D , the latch assembly  110  is shown moving from an open position as shown in  FIG. 8  to a closed position as shown in  FIG. 9D . In  FIG. 9A , the striker  124  moves to the left, and as such, rotates the claw  114  in a counter-clockwise direction. Contact between a first safety abutment  138  and the claw abutment  146  causes the pawl  116  to rotate in a clockwise sense about the pawl axis X. The pawl  116  rotates against the bias of the spring  166 . 
         [0072]      FIG. 9B  shows the position wherein the first safety abutment  138  has passed the claw abutment  146 , and thus the pawl  116  returns to its reset position with the chassis abutment  148  contacting the stop pin  130 . Further ingress of the striker  124  rotates the claw  114  further counter-clockwise as shown in  FIG. 9C  such that the closed abutment  140  acts on the claw abutment  146  in order to rotate the pawl  116  again. Rotation occurs until the closed abutment  140  passes the claw abutment  146  and the pawl  116  returns to its reset position, as shown in  FIG. 9D . As the door is now in a shut condition, the seal loads F are restored (as shown in  FIG. 5 ), and the latch assembly  110  is ready for release. It will be noted that when moving from the  FIG. 8  position, through the  FIG. 9A ,  9 B,  9 C positions to the  FIG. 9D  position, the pawl axis X remains in the same position. 
         [0073]    It will be appreciated that for the reasons described with respect to the latch assembly  10 , the friction involved in rotating the pawl  116  relative to the pawl pivot pin  168  in the latch assembly  110  is significantly reduced. Therefore, opening of the latch assembly  110  (i.e., movement from the position shown in  FIG. 5  to the position shown in  FIG. 7 ) involves less frictional force, reducing the likelihood that the latch assembly  110  becomes stuck in the closed position. Furthermore, relative rotation between the pawl  116  and the pawl pivot pin  168  during closing (as shown in  FIGS. 9A to 9D ) is also reduced, making it significantly easier to close the latch assembly  110 . 
         [0074]    It will also be appreciated that these benefits come through the reduction in the radius A of a first arcuate portion  156  on a lug  154 , as shown in  FIG. 8 . There is no associated loss in strength of the pawl pivot pin  168  due to its form incorporating the cylindrical body  152  and the lug  154 . 
         [0075]    The reduction in friction in the system results in a reduction in the aforementioned minimum backdrive angle. The start angle of the latch assembly  110  is indicated at H in  FIG. 5 . The present invention allows this angle to be reduced to levels significantly lower than known latches (i.e., the minimum backdrive angle is reduced) to levels in the order of 14.4 degrees (compared to known latches with, for example, minimum backdrive angles in the order of 54 degrees). 
         [0076]    It will be appreciated that the latch assembly  110  is an arrangement in which the force G acts to the left of pivot axis Y in  FIG. 5 . Therefore, the latch assembly  110  is only held closed by the presence of the lever abutment  178  acting on the lever  172 . It will be appreciated that the present invention extends to intrinsically stable latches, as will be described below. 
         [0077]    A latch assembly  210  is substantially similar to the latch assembly  110  and common features have reference numerals  100  greater. The main difference between the latch assembly  110  and the latch assembly  210  is that a pawl pivot pin orifice  282  and a lug  284  are oriented differently to a pawl pivot pin orifice  150  and the lug  154 . In this way, the latch assembly  210  is configured such that a force F acting from a striker  224  produces a force G resulting from the interaction between a closed abutment  240  and a claw abutment  246  such that the force G acts directly through both the pawl axis X and the pivot axis Y. As such, a pawl pivot pin  218  acts as a crank arm at a top dead center position i.e., in unstable equilibrium. No resulting torque is felt on either a pawl  216  or the pawl pivot pin  218  as a result of the force G, however movement of the force G to either side of the pivot axis Y will result in a torque being produced on the pawl  216 . 
         [0078]    Referring to  FIG. 11 , an actuator  286  including an actuation member  288  is connected to a lever  272 . The lever  272  sits against a lever abutment  278  mounted onto a latch retention plate  220 . 
         [0079]    In order to release the latch assembly  210 , the actuator  286  is actuated such that the actuator member  288  rotates the lever  272  in a counter-clockwise direction when viewing  FIG. 11 . This results in a rotation of the pawl pivot pin  218  in a clockwise direction shown in  FIG. 10  about the pivot axis Y. The line of action of force G therefore moves to the left of the pivot axis Y and acts to further rotate the pawl pivot pin  218  in order to release the latch assembly  210  in the same manner as described for the latch assembly  110 . The latch assembly  210  is reset in a similar way to the latch assembly  110  (and as such as described below with respect to  FIGS. 15A and 15B ). 
         [0080]    The latch assembly  210  is closed in substantially the same was as the latch assembly  110 . It should be noted that as well as an arrangement whereby the pawl pivot pin  218  is held at top dead center as shown in  FIG. 10 , a lever abutment  270  could be relocated such that the pawl pivot pin  218  sits at over top dead center; i.e., force G acts to the right of pivot axis Y. This provides an even more stable arrangement whereby it would be necessary to rotate the pawl pivot pin  218  such that the line of action of the force G passes through the pivot axis Y and beyond in order to unlatch the latch assembly  210 . 
         [0081]    As described with the latch assemblies  10  and  110 , the latch assembly  210  exhibits the same beneficial effects of the presence of the lug  284 . Generally, latch friction is reduced, and as such, the latch assembly  210  is easier to operate, requiring smaller actuators thereby reducing latch size. 
         [0082]    It will be noted that the relative sizes of the pawl pivot pin  18 ,  168 ,  218  and the pawl pivot pin orifice  50 ,  150 ,  282  can be varied to both permit and limit the relative motion between the pawl pivot pin and the pawl  16 ,  116 ,  216 . As seen in all of the above embodiments and specifically with reference to the latch assembly  10 , the pawl pivot pin  18  contacts the pawl  16  at a contact point  21  distant from the lug  54 . The contact point  21  is able to slide across the third arcuate portion  60  in order to increase stability of the latch assembly  210  and prevent excessive relative movement between the pawl pivot pin  18  and the pawl  16 . 
         [0083]    Referring to  FIGS. 12 and 13 , in a fourth embodiment of the present invention, a latch assembly  310  is shown. The latch assembly  310  operates in substantially the same way as the latch assembly  110  and includes a latch chassis  312  onto which are mounted a claw  314  rotating about a claw pin  316 , a toggle member  318  rotating about a toggle pin  320 , and a pawl  322  rotatable about a pawl pivot pin  324  mounted on the toggle member  318 . 
         [0084]    The toggle member  318  includes a toggle abutment  326 , which engages a moveable abutment  328  mounted onto the latch chassis  312  via an actuator  330  to rotate about an abutment axis Z. The pawl  322  and the toggle member  318  are biased into the position shown in  FIG. 12  via a spring  332 . In known arrangements (e.g., GB2409706), the pawl pivot pin is rotatable in a pawl pin orifice, which is often circular and of a diameter similar to the pawl pivot pin. 
         [0085]    In the present embodiment, there is provided a pawl pin orifice  334  in the shape of an obround with opposing end semi circle portions  336  of diameter substantially equal to a diameter of the pawl pivot pin  324 . The pawl pin orifice  334  further includes a neck  338  of a width that is substantially less than a diameter of the pawl pivot pin  324 . As such, the pawl pivot pin  324  is held in position relative to the pawl  322 . This can be seen in comparing  FIGS. 12 and 13 , whereby the actuator  330  has been actuated such that the moveable abutment  328  moves out of the way of the toggle abutment  326  and allows the toggle member  318  and the pawl  322  to collapse to a position whereby the claw  314  may rotate and release the associated striker. 
         [0086]    It can be clearly seen that the contact area between the pawl pivot pin  324  and the pawl pin orifice  334  is substantially less than if the pawl pin orifice was circular. As such, the frictional effect of dust and contaminants in this rotational joint is substantially reduced, and effort required to open and close the latch is also reduced. No reduction in the necessary size of the pawl pivot pin  324  has been made, only an increase in the size of the pawl pin orifice  334 . It should also be noted that the action of rotation of the pawl pivot pin  324  in the pawl pin orifice  334  will tend to force dust and contaminants from the mating areas of the two components into the empty parts of the pawl pin orifice  334  proximate the neck  338 . 
         [0087]    All of the above embodiments utilize dead pivots; i.e., the pawl includes a pawl pin orifice in which the pawl pivot pin rotates relative to the pawl. In such devices, the pawl pin orifice is defined in the pawl. The present invention also extends to live pivot arrangements; i.e., where the pawl pivot pin is fixably mounted to, or integral with, the pawl so it cannot rotate or otherwise move relative to the pawl. The pawl pin orifice is therefore defined in the component on which the pawl is rotatably mounted (e.g., the latch chassis, eccentric or toggle). 
         [0088]    The latch assembly  410  as seen in  FIGS. 14A and 14B  utilizes a live pivot arrangement. Components are substantially similar to the latch assembly  10 ,  400  greater, with the exception of the latch retention plate  420  and the pawl  416 . In the case of the latch assembly  410 , the pawl  416  is integral with a pawl pivot pin  468  protruding from the retention plate side thereof (as may be seen in  FIG. 14B ). The latch retention plate  420  includes a pawl pin orifice  482  similar in shape to the pawl pivot pin orifice  50 , although defined on the latch retention plate  420  and with the second arcuate portion facing in the opposite direction to the second arcuate portion  58 . 
         [0089]    In operation, the latch assembly  410  operates in substantially the same way as the latch assembly  10 , with the exception that the pawl pivot pin  468  rotates relative to the latch retention plate  420 , and remains stationary relative to the pawl  416 . 
         [0090]    A latch subassembly  500  as seen in  FIG. 14C  also utilizes a live pivot arrangement. A pawl  502  defines a pawl pivot pin  504  which is inserted into a pawl pin orifice  506  defined in an eccentric  508  such that the pawl  502  rotates about a pawl axis X. The eccentric  508  is rotationally mounted to a chassis  510  via the interaction of an eccentric pin  512  and an eccentric pin orifice  514  defined in the chassis  510 . As such, the eccentric  508  rotates about a pivot axis Y. This arrangement could be used instead of the dead pivot arrangement shown in latch assembly  110 , for example. 
         [0091]    An example reset mechanism is shown in  FIGS. 15A and 15B  with respect to a latch assembly  1110 , which is substantially similar to the latch assembly  110  with reference numerals  1000  greater. In addition to the latch assembly  110 , the latch assembly  1110  is provided with a reset pin  1500  defined on a claw  1114  and a reset lever  1502  mounted fast to a pawl pivot pin  1168  such that it rotates about the pivot axis Y with the pawl pivot pin  1168 . A reset abutment  1504  is defined on the reset lever  1502 . 
         [0092]    As mentioned, upon opening once the claw  1114  has rotated clockwise with the first safety abutment  1138  passing the pawl  1116 , the claw  1114  is then free to rotate to the fully open position as shown in  FIG. 15A . In doing so, the reset pin  1500  engages and then moves the reset abutment  1504  of the reset lever  1502 . This in turn rotates the pawl pivot pin  1168  from the position shown in  FIG. 7B  (with respect to pawl pivot pin  168 ) to the position shown in  FIG. 15A , thereby resetting the pawl axis X to the equivalent position (with respect to pawl pivot pin  168 ) as shown in  FIG. 8 . At the same time, with reference to  FIG. 15B , a release lever  1172  is returned to the position shown in hidden line, abutting a moveable abutment  1174 . The latch assembly  1110  is now reset. 
         [0093]    It will be understood that the pawl pin orifice may be defined in either or both of the retention plate and backplate and for optimum strength will be defined in both. 
         [0094]    It is envisaged that other live pivot arrangements fall within the scope of the present invention. For example, the pawl pin orifice could be formed in an eccentric with the pawl pivot pin (integral with the pawl) rotatably mounted therein. 
         [0095]    The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Summary:
A latch assembly includes a chassis, a latch bolt, movably mounted on the chassis and having a closed position for retaining a striker and an open position for releasing the striker, and a pawl having an engaged position at which the pawl is engaged with the latch bolt to hold the latch bolt in the closed position and a disengaged position at which the pawl is disengaged from the latch bolt thereby allowing the latch bolt to move to the open position. The pawl is rotatably mounted via a pawl pivot pin about a pawl axis, and the pawl pivot pin includes a first arcuate portion having a first radius about the pawl axis. A cross-sectional area of the pawl pivot pin, taken perpendicular to the pawl axis, is greater than an area of a circle having the first radius.