A latch mechanism includes a power actuator that does not require back driving of the drive train. The latch mechanism includes a latch bolt movable between a primary latched position and an open position. A first pawl secures and releases the latch bolt by moving between a latched position and released position. A release device moves between an engaged position, which allows the first pawl to reach an engaged position, and a released position, which retains the first pawl in its released position. A second pawl moves between an engaged position, which retains the release device in its released position, and a released position, which releases the release device.

This patent application claims priority to Great Britain Patent Application No. GB 9915432.0 filed on Jul. 1, 1999 and PCT Application PCT/GB00/02540, filed on Jun. 30, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to latch assemblies, and in particular latch assemblies which are manually operable alone or latch assemblies which are both manually operable and power actuator operable. 
     The present invention is particularly applicable to latches used on vehicle doors such as car passenger doors or car trunk doors. 
     Vehicle door latches are known which are released using a power actuator. Typically the door latch would have a latch bolt retained in position by a pawl and the actuator would act on a release lever connected to the pawl or would act directly on the pawl to release the latch. After the actuator's power stroke, the actuator must return to its initial state in one of three traditional methods: 
     a) Reverse energizing of the motor such that the motor is spun in its opposite direction e.g., reversing the polarity on an electric motor, 
     b) Declutching a clutch mechanism situated between the motor and a drive train of the actuating mechanism and returning the drive train by a weak spring, 
     c) Back driving the whole of the actuator mechanism including motor and drive train a strong spring. 
     The problem with reversing the polarity is that many modern vehicle controllers do not allow reverse polarity and more noise is generated due to longer motor operating duration. 
     The problem with an actuator incorporating a clutch mechanism is that the clutch mechanism itself is expensive, complex and has several parts and that such clutches do not operate consistently. 
     The problem with back driving the motor and power train is that the motor must be more powerful (and thus more expensive and heavier) to overcome the strong spring, more noise is generated due to longer operating duration, and some systems using helical gears cannot be back driven due to the large lead angle of the helical gears. 
     Known latch assemblies have primary latched positions wherein the associated door is fully closed and secondary latched positions wherein the associated door is not fully shut but nevertheless is prevented from opening. Such an arrangement has been used particularly on passenger doors of cars as a safety feature and in a legal requirement in many countries. Typically the door seals situated around the periphery of the door, which provide a weather tight seal between the door and its associated aperture, are resilient and are compressed when the door is in its closed condition. Releasing of the latch then allows the seals to partially open the door, at least past the secondary latched position, allowing the user to then fully open the door. 
     However a problem with such an arrangement is that under some conditions the seal force which tends to open the door can be insufficient to push the latch bolt past the secondary latched position resulting in a door that only opens to the secondary latched position. Under such circumstances the latch has to be unlatched again from the secondary latched position either manually by pulling on a door handle again or in the case of an actuator driven latch by operating the actuator for a second time and pulling the door open. Insufficient seal load could be caused by a door frozen into a closed position, poor fit/misalignment of the door, heavy vertically opening rear trunk lids. 
     It is an object of the present invention to provide a latch assembly including a power actuator which does not require to be driven in a reverse direction. 
     It is another object of the present invention to provide a latch assembly including a power actuator which does not require clutch mechanisms between a motor and a drive train of the power actuator. 
     SUMMARY OF THE INVENTION 
     It is another object of the present invention to provide a latch assembly including a power actuator which does not require back driving of the drive train and motor. 
     It is another object of the present invention to provide a latch assembly having a latch mechanism that does not engage a secondary latch position when operated. 
     Thus according to the present invention there is provided a latching mechanism including a latch bolt moveable between a primary latched position and an open position, 
     a first pawl moveable between a first engaged position where it secures the latch bolt in at least its primary latched position and a second released position where it releases the latch bolt from at least its first primary latched position, 
     release means moveable between a first engaged position where it allows the first pawl to achieve its first engaged position and a second released position where it retains the first pawl in its second released position, and 
     a second pawl moveable between a first engaged position where it is capable of retaining the release means in its second released position and a second released position where it releases the release means from its second released position 
     such that the latch mechanism can be latched and unlatched. 
     According to a further aspect of the present invention there is provided latch mechanism including a power actuator, the power actuator having a motor and a drive train, the drive train having at least one abutment for engagement with a release means of the latch mechanism, energization of the motor causing the abutment to move the release means from a first engaged position to a second released position to release the latch, in which a retention means ( 58 ) is capable of retaining the release means in its second released position. 
     According to a further aspect of the present invention there is provided a latch mechanism including a power actuator, the power actuator having a motor and a drive train, the drive train having the plurality of abutments for engagement with a release arrangement of the latch mechanism, energization of the motor causing one of the plurality of abutments to move the release arrangement from a first engaged position to second released position to release the latch, resulting in another of the plurality of abutments co-operating with the release arrangement to provide a drive train stop. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the drawings in which: 
     FIG. 1 is a view of a latch assembly according to the present invention in a closed condition; 
     FIG. 2 is a view of the latch assembly of FIG. 1 shown in an unlatching condition; 
     FIG. 3 is a view of the latch assembly of FIG. 1 shown in a latch opening condition; 
     FIG. 4 is a view of the latch assembly of FIG. 1 shown in a latching condition whereby super-imposed views of the rotating claw are shown in a primary latched position and secondary latched position; and 
     FIGS. 5 and 6 are views of a second embodiment of a latch assembly according to the present invention in an open and closed condition. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  4  there is shown a latch assembly  10  including a power actuator  12 , a latch mechanism  14  and a manual release means  16 . 
     In use the latch assembly  10  would be mounted on a door. 
     The power actuator includes a motor  18  having a motor shaft  20  drivingly connected to a pinion  22 . The power actuator further includes a drive train in the form of a rotor  24 . 
     Rotor  24  is journaled for rotation on plate  26  which forms part of the chassis of the latch assembly. Rotor  24  includes a set of gear teeth  28  which together with pinion  22  form a worm/worm gear drive arrangement. The rotor further includes three circumferentially equispaced posts  30 A,  30 B,  30 C, which project out of the plane of the paper of FIG.  1 . 
     The latched mechanism includes a latch bolt in the form of a rotating claw  32  having a mouth  34 , a primary latching abutment  36 , a secondary latching abutment  38  and a trip abutment in the form of a pin  40 . The claw  32  is pivotally mounted about pivot  42  on plate  26 . 
     Plate  26  includes a mouth  27  which in conjunction with the mouth  34  provides for the retention and release of a striker pin (not shown) mounted on an associated door aperture. 
     The rotating claw  32  is biased in a clockwise direction as shown in FIG. 1 by a resilient means (not shown), though in further embodiments this need not be the case. 
     The latch mechanism further includes a first pawl  44  pivotally mounted for rotation about pivot  46 . Pawl  44  includes a pawl tooth  48  for engagement with the primary and secondary latching abutments  36  and  38  of the rotating claw. Also mounted rotationally about pivot  46  is a release lever  50  having first, second and third arms  52 , 54 , 56  respectively. Release lever  50  is biased in an anticlockwise direction by a resilient means (not shown) operably acting between the release lever  50  and the plate  26 . 
     A further resilient means (not shown) operates between the first pawl  44  and release lever  50  to bias the first pawl  44  in an anticlockwise direction relative to the release lever  50 . Abutment  44 A on the first pawl and abutment  50 A release on the lever cooperates to limit the anticlockwise movement of the first pawl relative to the release lever. 
     The latch mechanism further includes a second pawl  58  rotatably mounted about pivot  60  which is turn is mounted on plate  26 . Second pawl  58  includes a hook  62  remote from pivot  60  and also a cam surface  64 . Second pawl  58  is biased in an anticlockwise direction by a resilient means (not shown) operating between the second pawl  58  and the plate  26 . An abutment (not shown) prevents the second pawl  58  from rotating further anticlockwise than is shown in FIG.  1 . 
     Mounted on second pawl  58  is a third pawl  66  pivotally mounted about pivot  68 . Third pawl  66  is arranged such that it can pivot anticlockwise about pivot  68  as a result of contact with pin  40  when the rotating claw  32  moves from a position shown in FIG. 1 to a position shown in FIG. 3 i.e. in an opening direction but cannot rotate about pivot  68  clockwise from the position shown in FIGS. 1 and 4 when the rotating claw  32  (and hence the pin  40 ) moves from the position as shown in FIG. 4 to the position as shown in FIG. 1 i.e. in a closing, there being an abutment (not shown) to prevent any such clockwise rotation. 
     In further embodiments the third pawl could be mounted on the chassis of the latch assembly and nevertheless co-operate with the second claw  58  and pin  40  to release the latch mechanism as described below. 
     The manual release means  16  comprises a boss  70  having three equispaced lobes  72 A,  72 B and  72 C which bear on an inner surface of the rotor  24  to allow rotation of the boss  70  relative to the plate  26 . Lobe  72 A includes a post  74  projecting out of the plane of the paper of FIG. 1 substantially parallel to post  30 A. 
     Lobe  72 B further includes an arm  76  having a hole  78  at an end remote from the boss for connection with a manually operated release cable (not shown). 
     The boss  70  further includes a centrally splined portion  80  for engagement with a manually operable key barrel (not shown). 
     Operation of the latch assembly is as follows 
     With reference to FIG. 1 the latch assembly is shown in a closed position whereby the rotating claw is held in its latched position by the first pawl  44  which is in its corresponding first engaged position whereby tooth  48  engages the primary latching abutment  36 . The release lever  50  is shown in its first engaged position and the second pawl  58  is shown in its first engaged position and the second pawl  58  is shown substantially in its first engaged position though as shown in FIG. 1 second pawl  58  is not engaging third arm  56  (see below). 
     The motor is energized for say 800 milliseconds, causing the rotor  24  to rotate anticlockwise in the direction of arrow A of the FIG. 2 resulting in post  30 A engaging and moving first arm  52  to the position shown in FIG.  2 . Clearly this movement of first arm  52  causing the release lever  50  and the first pawl  44  to both rotate about pivot  46  in a clockwise direction as shown by arrows B and C, thus disengaging pawl  48  from primary latching abutment  36 . 
     During movement of release lever  50  from its first engaged position as shown in FIG. 1 to its second released position as shown in FIG. 2, the third arm  56  initially engages cam surface  64  causing second pawl  58  to rotate clockwise about pivot  60 . Once the third arm  56  has passed the cam surface  64 , the bias means (not shown) biases the second pawl  58  anticlockwise about pivot  60  such that the third arm  56  is engaged behind the hook  62 , thus retaining the release lever  50  in the position as shown in FIG.  2 . In this position the end of second arm  54  acts as a stop abutment in co-operation with post  30 C preventing further rotation of rotor  24 . 
     Typically the time taken to move from the position as shown in FIG. 1 to the position as shown FIG. 2 might be 500 milliseconds, thus the motor would be stalled for the last 300 milliseconds of the 800 millisecond motor energization as a result of post  30 C abutting the end of second arm  54 . 
     Once the latch assembly has achieved the position as shown in FIG. 2 the latch claw is free to rotate in a clockwise direction as shown by arrow E of FIG. 3 thus releasing the striker from the mouth  27  and allowing the door, or trunk lid, etc. to open. 
     Note that in FIG. 2 the latch bolt is shown in its primary latched position though is free to rotate to its open position, the first pawl is shown in its second released position, the release lever is shown in its second released position, and the second pawl is shown in its first engaged position whereby it engages third arm  56 . 
     Further note that first pawl  44  is maintained in its second release position by co-operating abutments  44 A and  50 A, and the release lever is maintained in its second release position by the second pawl. Thus it is the second pawl that maintains the first pawl in its second release position via the intermediary of the release lever  50 . 
     As described above during the movement of the rotating claw from the position as shown in FIG. 2 to the position as shown in FIG. 3, the pin  40  trips past the third pawl  66  without affecting the position of the second pawl  58  which continues to retain third arm  56  and hence the release lever  50  in its second released position. 
     It should be noted that during movement of the rotating claw from the position as shown in FIG. 2 to the position as shown in FIG. 3, the pawl tooth  48  of the first pawl  44  is held out of engagement with the rotating claw and thus cannot engage the secondary latching abutment  38  as it passes underneath the pawl tooth  48 . 
     Subsequent closing of the door associated with the latch assembly  10  causes the striker pin (not shown) to enter mouth  27  and mouth  34  resulting in the rotating claw  32  rotating anticlockwise in a closing direction as shown by arrow F of FIG. 4 to a secondary latched position as shown by profile X of rotating claw  32  or, the door is slammed hard enough, to a primary latched position as shown by profile Y of the rotating claw  32 . This causes pin  40  to contact the third pawl  66  which, as described above, cannot rotate from the position shown in FIG. 4 clockwise relative to the second pawl  58 . Thus the pin  40  causes the third pawl  66  and second pawl  58  to both rotate in unison clockwise as shown by arrow G about pivot  60 . This action disengages the hook  66  from the end of third arm  56  allowing the release lever  50  and first pawl  44  to rotate anticlockwise as shown by arrows H and J thus re-engaging pawl tooth  48  with the primary or secondary latching abutment  36  or  38  as appropriate. 
     It should be noted that the relative positions of the pin  40 , secondary latching abutment  38  and first pawl  44  is such that the hook  66  is caused to disengage the end of third arm  56  just before the secondary latching abutment  38  passes under pawl tooth  48 . Thus in the event that the door is not slammed hard enough to be fully closed the pawl tooth  48  will nevertheless engage the secondary latching abutment  36  as described above. 
     Note that pin  40  moves past second pawl  58  when the rotating claw  32  moves from the closed position as shown in FIG. 1 to the open position as in FIG. 3 without affecting the position of the second pawl. Furthermore pin  40  again moves past second pawl  58  when moving from the open position as shown in FIG. 3 to the closed position as shown in FIG. 1, however, under these circumstances it does affect the position of the second pawl as it moves past the second pawl. 
     Subsequent energizing of the motor  18  following closing of the latch as shown in FIG. 4 will unlatch the door in a similar sequence as described above, but note that post  30 C (as opposed to post  30 A as described above) is now positioned to act on first arm  52  to open the latch. In this case since there are three posts  30 A,  30 B and  30 C, a single energizing operation of motor  18  results in rotor  24  only rotating through 120 degrees. 
     In further embodiments there may be more or less than three posts connected to the rotor. 
     Manual operation of the manual release means  16  by either operation of the cable connected to hole  78  or operation of the key barrel engaged with splined portion  80  results in post  74  rotating anticlockwise and engaging and moving first arm  52  in a manner similar to that as described above wherein post  30 A engages and moves first arm  52 . Note that during this manual disengagement the pawl tooth  48  cannot engage the secondary latching abutment  38  since it is held away from the rotating claw by the release lever  50  which is secured in its second released position by hook  62  as described above in relation to power opening of the latch. 
     With reference to FIGS. 5 and 6 there is shown a second embodiment of a latch assembly  110  with features equivalent to latch assembly  10  labelled  100  greater. 
     A release arrangement  181  is formed by the combination of release lever  150  and pawl  144 . In this case release lever  150  and pawl  144  are rotationally fast relative to each other, though in further embodiments this need not be the case. 
     Rotor  124  includes 3 abutments H 1 , H 2  and H 3  at a central portion of the rotor which form a first set of abutments H. Rotor  124  also includes abutments J 1 , J 2  and J 3  at a peripheral region of the rotor which form a second set of abutments J. 
     The release lever  150  and first set of abutments H lie in a first plane and the pawl  144  and second set of abutments J lie in a second plane different from the first plane thus allowing the second set of abutments J to past underneath release lever  150  when the rotor  124  rotates. 
     Operation of the latch assembly  110  is as follows: 
     Consideration of FIG. 6 shows the latch assembly  110  in a closed position with pawl  148  acting against latching abutment  136  to retain the rotating claw  132  in the closed position. It should be noted that abutment H 1  is in contact with the end of release lever  150 . 
     Actuation of motor  118  causes the rotor  124  to rotate in anticlockwise direction when viewing FIG. 6 whereupon abutment H 1 , acting on the end of release lever  150  causes the release lever and pawl  144  to rotate in a clockwise direction to the position as shown in FIG.  5 . 
     It should be noted from FIG. 5 that abutment H 1  has just disengaged the end of release lever  150  but at the same moment pawl tooth  148  has engaged abutment J 2  thus stopping further rotation of the rotor and causing the motor  118  to momentarily stall until such time as the power to the motor is cut. Stopping the rotor  124  in this manner ensures that it is orientated in the correct position ready for its next operation. 
     One the power to the motor is cut then there is no longer any force acting between abutment J 2  and pawl tooth  148  whereupon the pawl  144  and release lever  150  can return to the position as shown in FIG. 6 (though with the rotor  124  and rotating claw  132  remaining in the position as shown in FIG. 5) awaiting a subsequent closure of the latch. 
     It should be noted that the release lever is sequentially operated by abutments H 1 , H 2  and H 3  and that the rotor  124  sequentially stopped by abutment J 1 , J 2  and J 3 . Furthermore the release lever is only ever operated by abutments H 1 , H 2  and H 3  and the rotor is only ever stopped by abutments J 1 , J 2  and J 3 .