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REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to United Kingdom Patent Application GB 0603242.9 filed on Feb. 17, 2006.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to latch assemblies, and in particular to latch assemblies for use with car doors and car boots (trunks).  
         [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 will release the latch, allowing the door to open. Subsequent closure of the door will automatically relatch the latch.  
         [0004]     To ensure that rain does not enter the vehicle, weather seals are provided around a peripheral edge of the doors which close against an aperture in a vehicle body in which the door sits. In addition to providing protection from the rain, the weather seals also reduce the wind noise. The ongoing requirement for improved vehicle occupant comfort requires minimization of wind noise, which in turn requires the weather seals to be clamped tighter by the door. The door clamps the seals by virtue of the door latch. Accordingly, there is a tendency for a seal load exerted on the door latch to be increased to meet the required increased occupancy comfort levels. Because the seal force on the latch is increased, the forces required to release the latch are correspondingly increased.  
         [0005]     U.S. Pat. No. 3,386,761 shows a vehicle door mounted latch having a rotatable claw which releasably retains a vehicle body mounted striker to hold a door in a closed position. The rotatable claw is held in the closed position by a first pawl, and the first pawl is held in the closed position by a second pawl. The second pawl can be moved to a release position by an electric actuator, which in turn frees the first pawl, which allows the rotatable claw to rotate to an open position. The system is arranged such that once the second pawl has disengaged the first pawl, the first pawl is driven to a release position by the seal load acting on the rotatable claw.  
         [0006]     US2004/0227358 shows a rotatable claw held in a closed position by a rotatable lever and a link. The rotatable lever can in turn be held in position by a pawl. Disengaging the pawl from the rotatable lever allows the rotatable lever, the link and the pawl to move to an open position. One end of the link remains in permanent engagement with the rotatable claw. The system is arranged such that once the pawl has disengaged from the rotatable lever, the rotatable lever and the link are driven to the open position by the seal load acting on the rotatable claw.  
         [0007]     EP0978609 shows a rotatable claw that can be held in a closed position by a pawl. The pawl is mounted on a cam. During an initial part of opening of a latch, the cam rotates relative to the pawl, thereby initially slightly increasing and then significantly reducing a seal load. During a final part of opening of the latch, the cam and the pawl rotate in unison, thereby disengaging a pawl tooth from a claw tooth. However, the arrangement is such that the cam must be driven by a motor to release the latch. In particular, in the closed position, the particular configuration of a cam axis, a pawl pivot axis and a pawl tooth is such that latch will remain shut. Thus, in the closed position, the pawl pivot axis (28 of EP0978609) lies just to one side of a line (31 of EP0978609) drawn between the cam axis and a point where the pawl tooth contacts the rotatable claw. Significantly, the pawl pivot axis must move towards this line for the latch to be opened. In other words, the pawl is at an over-center position such that the cam is driven in a closing direction when the latch has been closed.  
         [0008]     DE10214691 and U.S. Pat. No. 5,188,406 are similarly in an overcenter position when in the closed position.  
         [0009]     Thus, EP0978609, DE10214691 and U.S. Pat. No. 5,188,406 all show latches in which the component in direct contact with the claw (the pawl) is in a stable position. U.S. Pat. No. 3,386,761 and US2004/0227358 both show latches wherein the component in direct contact with the claw is in an unstable position and therefore requires a further component (the second pawl in U.S. Pat. No. 3,386,761 and the pawl in US2004/0227358) to hold the component that directly engages the claw in the unstable position.  
       SUMMARY OF THE INVENTION  
       [0010]     An object of the present invention is to provide a compact latch arrangement. Another object of the present invention is to provide a reduced force release latch that is reliable in operation.  
         [0011]     Thus, the present invention provides a latch assembly including a chassis and a rotatable claw-type latch bolt moveably mounted on the chassis. The latch bolt has a closed position for retaining a striker and an open position for releasing the striker. The latch bolt is provided with a latch abutment remote from a center of rotation. The latch assembly further includes a pawl having an engaged position for holding the latch bolt in the closed position and a disengaged position that allows the latch bolt to move to the open position. The latch assembly includes an eccentric arrangement defining a first axis and a pawl axis remote from the first axis. The pawl is rotatable about the pawl axis. The latch assembly also includes a reset lever rotatably fixed to the eccentric arrangement for mutual rotation with the eccentric arrangement about the first axis. A biasing lever is configured to transmit a biasing force to the reset lever at a position remote from the first axis and to the latch bolt via the latch abutment. The latch assembly includes a biasing device arranged to apply the biasing force to the biasing lever. The latch assembly is configured such that when the pawl retains the latch bolt in the closed position, the biasing lever applies a force to the reset lever to promote disengagement of the pawl, and such that when the pawl is disengaged, the biasing lever promotes the rotation of the latch bolt into the open position.  
         [0012]     According to another aspect of the present invention, a method of operating the latch assembly from a closed position to an open position includes the steps of releasing the eccentric arrangement for rotation about the first axis, rotating the reset lever with the biasing lever to disengage the pawl, and rotating the latch bolt with the biasing lever into the open position once the pawl has retracted to a predetermined extent. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0014]      FIG. 1  is a view of a backplate side of a latch of certain components of a latch arrangement according to the present invention in a closed position, and with the backplate omitted;  
         [0015]      FIG. 1A  is a view of the backplate side of the latch of certain components of the latch arrangement in the closed position, with the backplate omitted;  
         [0016]      FIG. 1B  is a view of the backplate side of the latch with further components in place in the closed position;  
         [0017]      FIG. 1C  is a view of the backplate side of the latch with further components in place in an opening position, respectively;  
         [0018]      FIG. 2  is a view of the backplate side of the latch of certain components of the latch arrangement of  FIG. 1  in the closed position with further components in place, and the backplate omitted;  
         [0019]      FIG. 3  shows certain components of  FIG. 2  in a released but not fully open condition while the latch is being opened; and  
         [0020]      FIG. 4  shows the same components as  FIGS. 2 and 3  in a fully open position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     With reference to the Figures, a latch assembly  10  includes a latch chassis  12 , a latch bolt in the form of a rotatable claw  14 , a pawl  16 , an eccentric arrangement in the form of a crank shaft assembly  18  and a release actuator assembly  20 . The latch assembly  10  is mounted on a door  8  (only shown in  FIG. 1 ).  
         [0022]     The major components of the latch chassis  12  are a retention plate  22  and a backplate  24  ( FIG. 1C ). The retention plate  22  is generally planar and includes a mouth  26  for receiving a striker (not shown). The retention plate  22  includes three threaded holes  27  whose edges are bent over to project out of the paper as shown in  FIG. 1 , which in use secure the latch assembly  10  to the door  8 . A claw pivot pin  28  and stop pins  29  and  30  protect from the retention plate  22 . The stop pin  29  includes a cylindrical outer surface  29 A, the purpose of which will be described below.  
         [0023]     The backplate  24  ( FIG. 1C ) includes holes  31 A and  31 B for receiving ends of the claw pivot pin  28  and the stop pin  29 , respectively. During assembly, the ends of the claw pivot pin  28  and the stop pin  29  are peened over to secure the backplate  24  relative to the retention plate  22 .  
         [0024]     The claw  14  is pivotally mounted on the claw pivot pin  28  and includes a mouth  32  for receiving the striker, a first safety abutment  33  and a closed abutment  34 . The claw  14  is generally planar and includes a biasing pin  37  which projects out of the general plane of the claw  14 .  
         [0025]     The pawl  16  includes a pawl tooth  40 , a first arm  41  having an abutment surface  42 , and a second arm  43 . The pawl  16  also has a pawl pivot hole  46  of an internal diameter D. The pawl  16  is biased in a counter-clockwise direction about a crank pin axis Y (see below) by a spring  47  engaging the second arm  43  when viewing  FIG. 1 .  
         [0026]     The major components of the crank shaft assembly  18  are a crank shaft  50 , a reset lever  51  ( FIGS. 2-4 ) and a release lever  52  ( FIGS. 1B and 1C ).  
         [0027]     The crank shaft  50  includes a crank pin  54  in the form of disc having a crank pin axis Y. A square shaft  55  projects from one side of the crank pin  54 , and a cylindrical pin  56  (shown in broken lines in  FIG. 1 ) projects from the other side of the crank pin  54 . In other embodiments, alternative forms of the crank shaft  50  may be provided (e.g., other non-circular profiles) to cause components to be rotationally fixed thereto. The square shaft  55  and the cylindrical pin  56  together define a crank shaft axis A. The cylindrical pin  56  is rotatably mounted in a hole (not shown) of the retention plate  22 . The retention plate  22  thereby provides a bearing for the cylindrical pin  56 . An end of the square shaft  55  is provided with a threaded hole  57 .  
         [0028]     The diameter of the crank pin  54  is a running fit in the pawl pivot hole  46 , i.e., the diameter of the crank pin  54  is slightly less than the internal diameter D. The crank pin axis Y therefore defines a pawl axis about which the pawl  16  can rotate (see below). The thickness of the crank pin  54  is substantially the same as the thickness of the pawl  16 .  
         [0029]     A reset lever  51  is fitted to the square shaft  55  directly above the crank pin  54  and includes a first arm  60 , a second arm  63  and a boss  61  secured intermediate the first arm  60  and the second arm  63 . The boss  61  has a cylindrical outer surface  62  and a central hole of square cross section. Accordingly, when the reset lever  51  is assembled onto the square shaft  55 , as shown in  FIG. 2 , the first arm  60  becomes rotationally fixed with the crank shaft  50 . The cylindrical outer surface  62  of the boss  61  is mounted in a hole in the backplate  24 , which thereby provides a bearing surface for the cylindrical outer surface  62 . The cylindrical outer surface  62  and the outer surface of the cylindrical pin  56  are concentric and together define the crank shaft axis A.  
         [0030]     A biasing lever  80  is pivotably mounted to the second arm  63  proximate a first end  81  of the biasing lever  80  and extends above the pawl  16  and the claw  14  to contact the biasing pin  37  of the claw  14  proximate a second end  82  of the biasing lever  80 . The biasing lever  80  is further provided with a spring abutment  83  intermediate the first end  81  and the second end  82  and a biasing lever nose  84  offset from a plane of the biasing lever  80  to be capable of contacting the reset lever  51 .  
         [0031]     A biasing device in the form of a torsion spring  85  is secured to the retention plate  22  by the coil portion  86  that encircles one of the threaded holes  27  and a first leg  87  that is retained by a lug  88  of the retention plate  22 . A second spring leg  89  contacts the spring abutment  83  to apply a force FB to the biasing lever  80  that acts towards the right as illustrated in  FIG. 2 . A component of this force is transmitted both to the pivotable connection with the reset lever  51  as a force FR and by the contact between the biasing lever  80  and the biasing pin  37  as a force FC, when the claw  14  is in a closed position.  
         [0032]     The  60  includes an edge  60 A (also known as a reset abutment) which interacts with the biasing lever nose  84 , as will be described further below. The release lever  52  is generally elongate and includes a square hole  64  at one end to receive an end of the square shaft  55  and a release abutment  65  at the other end.  
         [0033]     A bolt and washer (not shown) is screwed into the threaded hole  57  of the square shaft  55  to secure the crank shaft  50 , the reset lever  51  and the release lever  52  together. Accordingly, the crank shaft  50 , the reset lever  51  and the release lever  52  are all rotationally fixed relative to each other.  
         [0034]     When assembled, the crank pin  54  and the reset lever  51  are positioned between the retention plate  22  and the backplate  24  with a cylindrical outer surface  62  of the boss  61  being rotationally mounted in a hole (not shown) of the backplate  24 . The release lever  52  lies on an opposite side of backplate  24  to the reset lever  51  and the crank pin  54  (best shown in  FIG. 1C ).  
         [0035]     The major components of the release actuator assembly  20  are a bracket  70 , an electromagnet  71  and a release plate  72 . The bracket  70  is bent from the backplate  24  and is used to mount the electromagnet  71 . The bracket  70  is also used to pivotally mount the release plate  72 , which is made from a magnetic material, such as steel. The release plate  72  is planar and generally rectangular in plan view and it can be seen from  FIG. 1B  that it projects equally either side of where it pivots on the bracket  70 . Thus, the release plate  72  is balanced.  
         [0036]     The release plate  72  is biased in a counter-clockwise direction when viewing  FIG. 1B  by the spring  73  (shown schematically). The release plate  72  includes an abutment  74  at one end. Other suitable forms of release actuator known in the art may be employed.  
         [0037]     Operation of the latch assembly  10  is as follows. Consideration of  FIGS. 1, 1A ,  1 B and  2  show the latch assembly  10  and the associated door  8  in a closed condition. The claw  14  is in a closed position, retaining the striker (not shown). The pawl  16  is in an engaged position whereby the pawl tooth  40  is engaged with the closed abutment  34 , thereby holding the claw  14  in the closed position. The weather seals of the door  8  are in a compressed state, and the striker therefore generates a seal force FS on the mouth  32  of claw  14 , which tends to rotate the claw  14  in a clockwise direction when viewing  FIG. 1 .  
         [0038]     The seal force FS in turn generates a force FP onto the pawl tooth  40  and hence onto the pawl  16 . The force FP is reacted by the crank pin  54  of the crank shaft  50 . The force FP reacted by the crank pin  54  is arranged to produce a clockwise torque on the crank shaft  50  about the crank shaft axis A. However, the crank shaft assembly  18  is prevented from rotating clockwise when viewing  FIG. 1  by virtue of the engagement between the release abutment  65  of the release lever  52  and the abutment  74  of the release plate  72 . The release plate  72  has been biased to the position shown in  FIG. 1B  by the spring  73 . Note that in the closed position, no electric current is flowing through electromagnet  71 , which accordingly exerts no magnetic force of the release plate  72 .  
         [0039]     At the same time, the biasing lever  80  exerts a force FC on the claw  14  via the biasing pin  37  urging it into an open, released condition. A force FR on the reset lever  51  promotes the turning of the crank shaft  50  in a clockwise direction.  
         [0040]     To release the latch assembly  10 , electric current is supplied to the electromagnet  71 , which creates a magnetic force which attracts the right hand end (when viewing  FIG. 1B ) of the release plate  72 , causing the release plate  72  to rotate clockwise to the position shown in  FIG. 2A . This in turn allows the release lever  52  and the crank shaft  50  to rotate clockwise (when viewing  FIGS. 1 and 2 ) in an opening direction as a result of the force FP being reacted by the crank pin  54  and of the force FR.  
         [0041]     Considering  FIG. 1 , upon opening, the rotation of the crank shaft  50  is clockwise about the crank shaft axis A. The crank shaft axis A is defined by the cylindrical pin  56  being rotatably mounted in the retention plate  22  (as mentioned above) and the boss  61  being rotatably mounted in the backplate  24  (as mentioned above). Accordingly, the crank shaft axis A is fixed relative to the latch chassis  12 .  
         [0042]     As mentioned above, when viewing  FIGS. 1 and 2 , the forces FP and FR generate a clockwise torque upon the crank shaft  50  about the crank shaft axis A. Once the crank shaft  50  is freed to rotate (i.e., once the abutment  74  has disengaged from the release abutment  65 ), then the crank shaft  50  will move in a clockwise direction because the crank pin axis Y is constrained to move about an arc centred on the crank shaft axis A. Because the pawl pivot hole  46  is a close running fit on the crank pin  54 , a pawl axis Z (i.e., the center of the pawl pivot hole  46 ) is coincident with the crank pin axis Y. Accordingly, the pawl axis Z is similarly constrained to move about an arc centred on crank shaft axis A.  
         [0043]     As the crank shaft  50  starts to rotate in a clockwise direction from the position shown in  FIG. 1 , the claw  14  starts to open. The action of the claw  14  pushing on the pawl  16  and the biasing lever  80  pushing on the reset lever  51  causes the pawl  16  to move. As the pawl  16  moves, the angular position of the pawl  16  is controlled by engagement between the abutment surface  42  of the first arm  41  and the stop pin  29 , more particularly a contact point B defined between the abutment surface  42  and part of the cylindrical outer surface  29 A.  
         [0044]     Generally speaking, the movement of the pawl  16  can be approximated to rotation about the contact point B (i.e., rotation about the contact point between the abutment surface  42  and the cylindrical outer surface  29 A). However, the movement is not truly rotational because a part of the pawl  16  (namely the pawl axis Z) is constrained to move about the crank shaft axis A rather than about the contact point B. Thus, the movement of the pawl  16  at the contact point B relative to the stop pin  29  is a combination of rotational movement and transitional (sliding) movement. Indeed, the contact point B is not stationary and will move a relatively small distance around the cylindrical outer surface  29 A and a relatively small distance along the abutment surface  42 . Thus, the contact point B is the position where (at the relevant time during opening of the latch assembly  10 ) the abutment surface  42  contacts the cylindrical outer surface  29 A.  
         [0045]     Starting from the  FIG. 2  position, once the abutment  74  has disengaged from the release abutment  65 , the force FR causes the biasing lever  80  to rotate clockwise about the biasing pin  37  (acting as a fulcrum), and the closed abutment  34  of the claw  14  pushes the pawl  16  (via the pawl tooth) to a position whereby the closed abutment  34  can pass under the pawl tooth  40  when viewing  FIG. 3 . Once the pawl tooth  40  has thus disengaged from the closed abutment  34  of the claw  14 , the claw  14  is then free to rotate past the position shown in  FIG. 3  to the fully open position as shown in  FIG. 4 , urged in this direction by the forces FS and FC.  
         [0046]     However, because the biasing pin  37  moves to the right, the biasing lever  80  pivots counter-clockwise about its pivotable connection with the reset lever  51  as it urges the claw  14  into the released position. At a predetermined point before or during this, the biasing lever nose  84  contacts the edge  60 A of the reset lever  51 . This may be before any rotation of the claw  14  has occurred (with contact occurring by virtue of the rotation of the crank shaft  50  alone) or once a certain amount of the claw  14  rotation has occurred.  
         [0047]     As a result of a force FT acting on the edge  60 A, the direction in which the biasing lever  80  urges the reset lever  51  reverses so that it is now counter-clockwise about the crank shaft axis A as a fulcrum rather than clockwise. Thus, beyond this predetermined point, the biasing lever  80  acts to reset the crank shaft  50  to the position shown in  FIG. 2  where it may re-engage the claw  14  and in which the release lever  52  rotates counter-clockwise back to the position shown in  FIG. 1B  in which it is retained by the release plate  72 . In other words, the crank pin axis Y resets to the  FIG. 1  position, and the release lever  52  is returned to the  FIG. 1B  position.  
         [0048]     As the reset lever  51  passes over the right hand end of release plate  72 , the release plate  72  is momentarily deflected and then snapped back into engagement (under the influence of the spring  73 ) such that the abutment  74  re-engages the release abutment  65 . Thus, when considering  FIG. 4 , the pawl  16 , the crank shaft assembly  18 , and the release actuator assembly  20  are all in the same position as FIGS.  1  to  1 B. However, in  FIG. 4 , the claw  14  is in the open position, whereas in FIGS.  1  to  1 B, the claw  14  is in the closed position.  
         [0049]     Once the latch assembly  10  and associated door  8  has been opened, closing of the door  8  will automatically relatch the latch assembly  10 . Note however, that no rotation of the crank shaft  50  occurs during closing of the door  8 . Accordingly, the crank pin axis Y does not rotate, and the crank pin itself acts as a simple pivot having a fixed axis.  
         [0050]     As mentioned above, the crank shaft assembly  18  is supported in a bearing of the retention plate  22  on one side of the crank pin  54  and is supported in a bearing in the backplate  24  on the other side of crank pin  54 . Thus, the crank shaft  50  is supported on both sides of the crank pin  54 , which is a particularly compact and strong arrangement. However, in further embodiments, the crank shaft  50  need only be supported on one side, i.e., the crank shaft  50  can be an overhung crank shaft  50 . An example of such an overhung crank shaft  50  would be provided by deleting the cylindrical pin  56 . Note that the crank shaft axis A would still be in exactly the same position because it would be defined by the cylindrical outer surface  62 .  
         [0051]     The arrangement of the present invention permits a single biasing device (spring) to perform the function of promoting release and resetting of a crankshaft mounted pawl, while also urging a claw  14  into an open position.  
         [0052]     The crank throw (the distance between the crank shaft axis A and the crank pin axis Y) is dimensioned, in this embodiment, such that no part of the cylindrical pin  56  sits outside the circumference of the crank pin  54 . This provides a particularly compact arrangement. In further embodiments, the crank pin axis Y can be offset from the crank shaft axis A by more than the radius of the crank pin  54 . In addition, suitable alternative biasing devices may be used in place of the torsion spring. The position at which the spring contacts the biasing lever  80  may be adjusted according to the proportion of the force required to be transmitted to the claw  14  and the reset lever  51 . The reset lever  51  could in alternative embodiments be integral with the crank shaft  50 . In addition, the reset lever  51  and the release lever  52  may be the same component. Furthermore, in a highly integrated design the crank shaft  50 , the reset lever  51  and the release lever  52  could all be a single component.  
         [0053]     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 and a rotatable claw-type latch bolt moveably mounted on the chassis. The latch bolt has a closed position for retaining a striker and an open position for releasing the striker. The latch bolt is provided with a latch abutment remote from a center of rotation. The latch assembly further includes a pawl rotatable about a pawl axis and having an engaged position for holding the latch bolt in the closed position and a disengaged position that allows the latch bolt to move to the open position. The latch assembly includes an eccentric arrangement defining a first axis and the pawl axis remote from the first axis. The latch assembly also includes a reset lever rotatably fixed to the eccentric arrangement for mutual rotation with the eccentric arrangement about the first axis. The latch assembly includes a biasing lever configured to transmit a biasing force to the reset lever at a position remote from the first axis and to the latch bolt via the latch abutment. The latch assembly includes a biasing device arranged to apply the biasing force to the biasing lever. The latch assembly is configured such that when the pawl retains the latch bolt in the closed position, the biasing lever applies a force to the reset lever to promote disengagement of the pawl, and such that when the pawl is disengaged, the biasing lever promotes the rotation of the latch bolt into the open position.