LATCH MECHANISM AND LATCH ASSEMBLY

Abstract: A latch mechanism (12) including a latching detent (44) for engagement with a relatively fixed striker (14) and moveable between first and second positions, a pawl (60) moveable between a first and second position and a control member (72) moveable between a first and second position, the pawl (60) in the first position blocking displacement of the detent (44) from its first position to latch the mechanism (12) and in the second position allowing the detent to move to its second position to release the latch from engagement with the striker, the control member (72) in the first position, allowing the pawl (60) to move between its first and second positions and in the second position placing the pawl (60) in its second position.

Description: LATCH MECHANISM AND LATCH ASSEMBLY The present invention relates to latch mechanisms and latch assemblies for use in closing doors and the like. In particular the invention relates to latch assemblies and latch mechanisms used in conjunction with vehicle doors. Known latch assemblies use a rotating claw mounted on a door, which when closed contacts a striker which causes the claw to rotate in a first direction and secure the door in a closed position. Rotation of the claw in the opposite (second) direction is prevented by a pawl directly engaging notches on the claw. The door can be subsequently opened by moving the pawl out of engagement with the notches and thus allowing the claw to rotate in the second direction and release the striker. However known latch assemblies require a relatively high force to release the pawl from the claw notch. Also such claws are mounted at the back of the vehicle door and are exposed. Such an arrangement makes it difficult to properly seal the area via door seals which necessarily have to be of complicated shape and therefore expensive. It is an object of the present invention to provide a latch assembly and a latch mechanism which requires relatively low release forces. It is also an object of the present invention to provide a latch assembly and latch mechanism which enables a substantially simpler sealing arrangement. Thus according to the present invention there is provided a latch mechanism according to claim 1 and a latch assembly according to claim 14 of the accompanying claims. The invention will now be described by way of example only with reference to the accompanying drawings in which; Figure 1 is an isometric view of a latch assembly according to the present invention; Figure 2 is a different isometric view of the latch assembly of Figure 1, shown with a retention plate removed for clarity; Figures 3 to 7 show elevation views of Figure 2 with the latch assembly being moved from and open to a fully latched position, and; Figure 8 is an elevation view of Figure 2 shown with the latch assembly in a release condition prior to withdrawal of the striker bar. With reference to Figures 1 to 3 there is shown a latch assembly 10 including a latch mechanism 12 and a striker bar 14. Striker bar 14 is of uniform thickness T and includes securing holes 16 (in this case two holes) used to secure the striker bar 14 to an adjacent component such as a door or B or C post of a vehicle. The profile of the striker bar 14 includes first and second teeth (18 and 20). Each tooth has a respective ramp portion (18A and 20A) and an abutment portion (18B and 20B). Striker bar also has a support surface 22. The latch mechanism 12 includes a cover plate 30 and a retention plate 32, held in spaced apart relationship by spacers 34 and 36. Each plate (30 and 32) includes securing holes 38 which align with appropriate spacers 34 and 36 to allow a fastener to secure the latch mechanism to a door. Guide member 40 includes a membrane (not shown) which lies substantially parallel and against the inner face of retention plate 32. The membrane conveniently includes holes through which the first pivot pin 46 and the second pivot pin 62 can pass thus securing the guide member 40 in position. Guide member 40 includes guides 41 and 42 which are upstanding from the surface of the membrane. Guide 41 includes an abutment 41 A. A latching detent 44 is pivotally mounted on a first pivot pin 46. First pivot pin 46 is supported at one end by cover plate 30 and at the other end by retention plate 32. Detent 44 is of constant thickness U and includes a latch tooth 48 having a latching abutment surface 50 and a camming surface 52. The detent further includes a first abutment surface 54, a second abutment surface 56 and a pawl stop 58. A pawl 60 is pivotally mounted on a second pivot pin 62 which in turn is supported at one end by cover plate 30 and at the other end by retention plate 32. Pawl 60 includes a first arm 64 with a first abutment surface 66 and a second arm 68 with a second abutment surface 70. A control member 72 is also pivotally mounted on first pivot pin 46. A major flat part of member 72 lies behind detent 44 and pawl 60 when viewing Figure 3. Member 72 includes a slot 72A (shown dotted in figure 3) to enable the second pivot pin 62 to pass through the member to engage the cover plate 30 and also to allow pivotal movement of the control member 72 about the first pivot 46 (see below). Member 72 also has a laterally projecting formation 73 at its distal end providing a first camming surface 74 and a second camming surface 76 which co-act with the pawl 60 and striker bar 14 respectively. Spring 61 (shown diagrammatically in figures 3 and 4) is located between the membrane portion of guide number 40, the guides 41 and 42 and the control member 72. One end of the spring 61 acts to bias pawl 60 in a clockwise direction about the second pivot pin 62 and the other end of spring 61 acts to bias control member 72 in a clockwise direction about the first pivot pin 46 by contact with stop pin 77 of control member 72. Stop pin 77 acts on detent 44 to bias it in a clockwise direction about first pivot pin 46. Such clockwise biasing of detent 44 is resisted by contact between first abutment surface 54 and abutment 41 A. Advantageously the ends of the first and second pivot pins 46,62 can be formed by peening methods or the like to secure the cover plate 30 to the retention plate 32. Operation of the latch assembly is as follows; Figure 3 shows the latch assembly 10 in a door open condition since the latch mechanism 12 is free to move in a closing direction A or an opening direction B and is not restrained by the striker bar 14. Detent 44 is biased to a first position wherein its first abutment 54 is in contact with the guide abutment 41 A. Member 72 is biased to a first position wherein a stop abutment (in this case the top of slot 72A) contacts a stop abutment (in this case second pivot pin 62) of the assembly. Pawl 60 is biased into a first position wherein first arm 64 contacts pawl stop 58 of detent 44. Figures 4 to 7 show a progressive engagement of the latch mechanism with the striker on closing the door. In Figure 4 member 72 has been caused to rotate anti-clockwise by its second camming surface 76 riding up the first tooth ramp 18 A. This movement of member 72 causes its first camming surface 74 to contact the second abutment surface 70 of pawl 60 resulting in the pawl 60 rotating in an anti-clockwise direction against the action of spring 61 to a second position. When the pawl 60 is in the second position the first abutment surface 66 of the pawl no longer contacts the second abutment surface 56 of the detent, and also the first arm 64 no longer abuts the pawl stop 58 of the detent 44. In particular the detent can rotate in an anti-clockwise direction when its camming surface 52 contacts the first tooth ramp 18 A. Figure 5 shows the latch in a first safety condition with the latch tooth 48 and second camming surface 76 of member 72 being positioned between the first tooth 18 and second tooth 20 of the striker bar 14. The detent, pawl, and control member are all in their first positions and in particular the detent 44 is blocked from moving by first abutment surface 66 of pawl 60 and therefore movement of the latch mechanism 12 in an opening direction B is prevented by first tooth abutment 18B contacting latching abutment surface 50 of detent 44. Further movement of the latch mechanism in a closing direction A results in the detent and member 72 riding over the second tooth 20 freed from the pawl in the same way as they rode over first tooth 18. Thus Figures 6 and 7 show the detent 44 pawl 60 and member 72 at the same relative position to each other as shown in Figures 4 and 5 respectively. Figure 7 shows the latch mechanism in a fully latched position holding the door closed, movement of the latch mechanism in an opening direction B being prevented by the engagement of second tooth abutment 20B and latching abutment surface 50. Figure 8 shows the latch assembly in a release condition to allow the door to open. Member 72 has been rotated to its second position by a release means (not shown) connected to for example a door handle and/or power actuator(not shown), in turn displacing pawl 60 to its second position. Application of a force F to the latch mechanism in an opening direction B results in this force being transferred through pin 46 to latch tooth 48 (see (F) Fig 8). This in turn results in an equal and opposite force F2 being applied to the latch tooth 48 by the second striker tooth 20. The latch assembly has been arranged such that the line of action of the force F2 does not pass through the axis of the first pivot pin 46. The perpendicular distance from the line of action of force F2 to the axis of the first pivot pin 46 is distance D. Thus applying force F to latch mechanism 12, on opening the door results in an anti-clockwise moment being applied to the detent 44 of value (F2 x D). This moment causes the detent 44 to pivot anti-clockwise and allows tooth 20 to pass under latch tooth 48 following which latch tooth 48 is biased by its spring into the gap between the first and second teeth of the striker bar. However by maintaining member 72 and pawl in their respective second position, further opening of the door will cause latch tooth 48 to ride over the first tooth 18 in a manner similar to that which caused it to ride over the second tooth 20, until the latch is fully released. It should be noted that in Figures 4 to 8 the support surface 22 of the striker bar 14 slides across spacer 36 and thus any turning moment of the striker bar 14 caused by force (F) acting about the axis of holes 16 can be reacted by spacer 36 within the latch mechanism as a whole. It should be noted that further embodiments according to the present invention are not restricted to the particular spacial relationship and orientation of the detent pivot axis, the direction of opening of the latch mechanism relative to the striker bar, and the orientation of the latching abutment surface of the detent and the first or second tooth abutment of the striker bar. Thus the co-operating latching abutment surface and striker bar tooth abutment need not be perpendicular to the direction of opening of the latch, provided that with the control member and pawl in their second positions, opening of the latch assembly causes a moment to be applied to the detent to move it out of engagement with the striker bar teeth.

Claims: CLAIMS 1. A latch mechanism including a latching detent for engagement with a relatively fixed striker and moveable between first and second positions, a pawl moveable between a first and second position and a control member moveable between a first and second position, the pawl in the first position blocking displacement of the detent from its first position to latch the mechanism and in the second position allowing the detent to move to its second position to release the latch from engagement with the striker, the control member in the first position, allowing the pawl to move between its first and second positions and in the second position placing the pawl in its second position. 2. A latch mechanism as defined in claim 1 in which at least one of the detent, pawl or control member is pivotally mounted. 3. A latch mechanism as defined in claim 2 in which the pivot axis of the detent is co-axial with the pivot axis of the control member. 4. A latch mechanism as defined in any previous claim in which the detent is biased to its first position by a first resilient means. 5. A latch mechanism as defined in any previous claim in which the pawl is biased into its first position by a second resilient means. 6. A latch mechanism as defined in any previous claim in which the control member is biased into its first position by a third resilient means. 7. A latch mechanism as defined in any previous claim in which a resilient means acts to bias at least two of the detent and pawl and control member into respective first positions. 8. A latch assembly including a latch mechanism as in any previous claim and a co-acting striker. 9. A latch assembly as defined in claim 8 in which the striker is in the form of a profiled flat bar. 10. A latch assembly as defined in claim 8 or 9 in which the striker is inserted between the detent and a striker support. 11. A latch assembly as defined in claim 8 or 9 or 10 in which the control member is moved from its first position to its second position by contact with a formation or formations of the striker which are also engaged by the detent. 12. A latch assembly as defined in any one of claims 8 to 11, the latch mechanism being mounted on a door and defining a striker aperture, the striker projecting from fixed structure of the vehicle in use, in which when the door is closed the striker extends into the striker aperture such that a portion of the door surrounding the striker aperture and the portion of fixed structure surrounding the striker are in face to face relationship. 13. A latch assembly as defined in any one of claims 8 to 12 in which when the striker is engaged with the latch mechanism, a latching abutment of the detent co- operates with an abutment of the striker to prevent disengagement of the striker from the latch mechanism and when a force is applied to the assembly to disengage the striker from the latch mechanism the co-operating abutments generate a force which acts to move the detent towards its second position. 14. A latch assembly which includes the latch mechanism being mounted on a door and including a striker aperture, the striker projecting from fixed structure of the vehicle, in which when the door is closed the striker projects into the striker aperture such that the portion of door surrounding the striker aperture and the portion of fixed structure surrounding the striker are in face to face relationship. 15. A latch assembly including a latch mechanism having a latching detent for engagement with a relatively fixed striker and moveable between first and second positions, a pawl moveable between a first and second position, the pawl in the first position blocking displacement of the detent from its first position to latch the mechanism and in the second position allowing the detent to move to its second position to release the latch from engagement with the striker, and a co-acting striking which when the striker is engaged with the latch mechanism a latching abutment of the detent co-operates with an abutment of the striker to prevent disengagement of the striker from the latch mechanism and when a force is applied to the assembly to disengage the striker from the latch mechanism the co-operating abutments generate a force which acts to move the detent towards its second position.

Inventors: SPURR NIGEL, SPURR, NIGEL
Applicants: MERITOR LIGHT VEHICLE SYS LTD, SPURR NIGEL, MERITOR LIGHT VEHICLE SYSTEMS (UK) LIMITED, SPURR, NIGEL
Application year: 1999
Main classification: E05B65
IPC codes: E05B65