GB2189539A - Overcentre fastening mechanism - Google Patents

Description

GB2189539A 1 SPECIFICATION Figure 1C is a top plan view of the as sembly

of Fig. 1.

Supplemental locking mechanism for a ten- Figure 1D is a side elevational view of what sion latch assembly is shown in Figs. 1 and 1 C.

70 Figure 2 is a plan view of the tension latch The present invention relates to latch mecha- assembly shown in Fig. 1 in assembled and nisms used in the aircraft and aerospace in- closed condition.

dustries, and in particular to locking mecha- Figure 3 is a view in crosssection of the nisms for overcenter tension latch assemblies. tension latch assembly as seen generally along The present invention is an improvement in 75 lines 3-3 in Fig. 2.

locking mechanisms for latches which use the Figure 3A is a view in crosssection of the overcenter concept, i.e. latches which employ tension latch assembly as seen generally along a pivot point which must be---overcenterfor lines A-A in Fig. 3.

the latch to remain securely locked. Such Figure 38 is a view in crosssection of the latches have typically been able to provide 80 tension latch assembly as seen generally along only limited secondary locking features for en- lines B-B in Fig. 3.

suring that the primary or overcenter locking Figure 4 is a view of what is shown in Fig.

mechanisms remain securely locked and func- 3 as an opening force is exerted on the tion properly when the latch is in use. For closed tension latch assembly.

example, the use of a locking trigger release 85 Figure 5 is a view of what is shown in Figs.

element is well known in the latch industry as 3 and 4 when the handle of the latch as a secondary locking feature. However, the de- sembly is in the open position.

velopment of new aircraft and space vehicles Figure 6 is a bottom plan view of what is demands latching reliability even in the event shown in Fig. 5.

of failure of the secondary locking feature. 90 Figure 7 is a crosssectional view of the Hence the development of the present inven- latch assembly shown under forces which tion. cause the handle and link mechanism to en According to the present invention there is gage for simultaneous movement for release provided an overcenter tension latch assembly of the latch hook from the keeper assembly.

having a handle, a latch hook, a keeper for 95 Figure 8 is a view of what is shown in Fig.

the latch hook, a fixed pivot point, a second 7, as the handle and link mechanism are pivot point rotatable about the fixed pivot po- moved to release the latch hook.

int, and a link mechanism engaging the handle Figure 9 illustrates the position of the latch and connecting the latch hook with the fixed hook as the tension latch assembly is un pivot point, the link mechanism permitting ro- 100 latched or released from the keeper.

tational movement of the second pivot point Figure 10 is a view of what is shown in about the fixed pivot point, the second pivot Figs. 5-9 of the tension latch assembly in its point being overcenter relative to the fixed pi- open and released positions.

vot point to provide a primary locking mecha- Figure 11 is a view of the tension latch nism when the latch hook is secured relative 105 assembly as the latch hook is moved into po to the keeper, wherein the improvement com- sition for re-securement with the keeper as prises: sembly.

means for preventing rotation of the link Figure 12 is a view of the preferred embodi mechanism, the hook and the second pivot ment subsequent to the movement illustrated point about the fixed pivot point when the 110 in Fig. 11.

latch hook is secured relative to the keeper Figure 13 is a view of the tension latch as a and forces are applied to the secured latch force is applied to bring the assembly over assembly tending to release the assembly center with respect to the fixed pivot point.

from an overcenter primary locked position, Figure 14 is a view illustrating the relative said rotation preventing means being conpositions of the secondary locking mechanism, structed and arranged to counteract such i.e. a trigger, as the latch assembly handle is forces and thereby provide a supplemental secured to the latch hook.

locking mechanism. With reference now to the drawings, the In order that the invention may be well un- same reference numerals are used throughout derstood there will now be described an em- 120 the drawings to indicate the same elements.

bodiment thereof, given by way of example Turning to Figs. 1-4 a handle 20, a keeper only, reference being made to the accompany- engaging member (or latch hook as it will ing drawings in which:- hereinafter be referred to) 50, and means for Figure 1 is an exploded view in perspective linking the handle 20 with the latch hook 50 of a preferred embodiment of tension latch 125 form the basic components of the tension assembly. latch assembly shown. For a point of refer Figure 1A is an enlarged top plan view of a ence only, words such as forward, rearward, spring used with the assembly of Fig. 1. paper and lower are used to assist the reader Figure 18 is an enlarged side elevational in orienting the various components with re- view of the spring shown in Figs. 1 and 1 A. 130spect to each other. Such references as herein 2 GB2189539A 2 used may not necessarily apply in all applica- The third basic component of the latch as- tions of the invention, e.g. when an embodi- sembly is the means for linking the handle 20 ment is mounted so that the handle opens in to the latch hook 50. A link mechanism 70 in a direction one-hundred and eighty degrees the preferred embodiment comprises a pair of from the orientation shown in the drawings. 70 individual links 70A, 70B of identical construc Persons skilled in the art will appreciate the tion. Each link has a forward, first end and a likelihood of such varied mountings and thus rearward, second end. In the forward end of any further explanation is not believed to be each link is an aperture 71. These forward necessary. most apertures 71 receive a rivet or pin 73.

The handle 20 in the illustrated embodi- 75 The pin 73 is secured therein so as to extend ments has a typical channel-shape construc- between the apertures 71 and protrude be tion in that it has a central top or base por- yond each link a sufficient distance which will tion 21 from which extend, opposite each allow the hook portions 34, 35 of the trigger other from either lengthwise edge of the base mechanism 30 to be captured by the protrud portion 21, a pair of identical side walls 80 ing portions of the pin 73. A second aperture 22,23. Accordingly the handle has what may 72 to the rear of the forward aperture 71 on be referred to as a forward, first end 24, and each link 70A, 70B is constructed so as to a rearward second end 25. A generally cen- receive a bushing 74 for mounting the latch trally located area of the base portion 21 is hook assembly to a part of the aircraft's formed with an opening 26 therein. Mounted 85 structure which is shown in phantom. The in the opening 26 by means of a rivet 27 or bushing 74 serves as a fixed pivot point in like element is a trigger mechanism 30. The the assembly. At the rearward, second end of particular trigger mechanism 30 shown in the each link 70A, 70B are two additional pairs of drawings is known in the art in that its upperapertures. The forwardmost apertures 75 at most wall 31 lies in flush relationship with the 90 the. link second end are sized to receive a handle base portion 21 when the trigger is in pivot pin 76 therebetween. The pivot pin 76 a locked position. Extending from the trigger pivotally mounts the second end of the latch top wall 31 and substantially parallel to the hook 50 to the second end of the link mecha handle sidewalls 22, 23 are a pair of arms nism 70 by an alignment of apertures 57, 58, 32, 33. Each arm 32, 33 has at its lowermost 95 75. The pin 76 is inserted therethrough and portion an indented or notched area forming a securely retained therein for rotatable move hook 34, 35 for capturing therein a portion of ment about the fixed pivot point or bushing an underlying link mechanism to be described 74. The second pair of apertures 77 at the further below. A conventional spring 36 is se- link mechanism second end are formed in cured with the rivet 27 in a manner such that 100 each link 70A, 70B at a position which per the trigger mechanism 30 may be pivoted mits an alignment of the apertures 77 with a about the rivet 27 when a portion of the trig- respective slot 40, 42 at the handle second ger wall 31 is depressed. end 25. A pivot pin 78 is thus inserted At the rearward end 25 of the handle 20 a through the aligned apertures 77 and slots 40, pair of slots 40, 42 are provided, one each in 105 42 to pivotally mount the handle to the link a respective side wall 22, 23. The slots 40, mechanism. The pin 78 may travel in the slot 42 are aligned with respect to each other and 40, 42 between the slots' two ends. Finally at have a pre-determined position and size rela- the upper edge of each link rearward end, tive to a portion of the link mechanism with adjacent the apertures 77, a detent or camm which it must cooperate. Each slot 40, 42 has 110 ing type surface 79 is formed so as to receive a forward end 40A, 42A respectively and a and capture a portion of the pin 78 therein rearward end 4013, 42B respectively. Forward when the handle is indexed into a second po of each slot 40, 42, is an aperture or through- sition. This feature will be explained further in hole 44, 45 through which a rivet 46 or like the operation of the preferred embodiment element passes and is secured between the 115 which follows.

two apertures 44, 45. A spring 80 is provided in order to bias the The latch hook 50 has a forward, first end handle 20 open when the handle 20 is re 51 and a rearward, second end 52. The first leased by the trigger 30 from locking engage end 51 has a downwardly extending portion ment with the link mechanism 70. The particu- formed so as to engage and capture a keeper 120 lar spring 80 shown has a unique configura 53 (shown in phantom in Fig. 1). This end 51 tion which may be best appreciated by a of the latch hook 50 is shown constructed so study of Figs. 1 A and 1 B in conjunction with that when engaged with a keeper 53, there Fig. 1. The spring 80 has a first coiled end will be substantially little room if any between 81 which bears upon a portion of the under the top edge 54 of the latch hook 50 and the 125 side of the handle second end 25 and a bear immediately adjacent handle top portion 21. ing block 89 attached thereto. Integrally The rearward or second end 52 of the latch formed with the first end 81 is a second end hook 50 is formed as a pair of rearwardly 82 whose coiled section 83 is oriented per extending arms 55, 56. Each arm has a rear- pendicular with respect to the coiled section wardmost through-hole 57, 58 respectively. 130 84 of the first end 8 1. When the latch hook 3 GB2189539A 3 assembly is installed the coiled section 83 of embodiment in its assembled, operable form the spring second end 82 surrounds and is may be appreciated. In Figs. 2- 14 the tension secured by the pin 78. The free end 85 of latch assembly is shown as it would appear in the second coil end 82 is formed in an L cross-section at various degrees of release shape configuration for capture upon and en- 70 and locking.

gagement with a portion of the invention pre- In Fig. 3 the latch hook 50 is shown in full ferred embodiment to be explained next. load engagement with the keeper 53 of the A preferred embodiment for the present inkeeper assembly. The handle is shown in its vention may be appreciated from a study of closed position and is locked to the link Figs. 1, 1C, and 1D. A mechanism is provided 75 mechanism pin 73 by the trigger 30. Both the which will prevent rotation of the link mecha- trigger wall 31 and the handle top portion 21 nism 70, the latch hook 50 and the pivot pin lie flush with the surface 100 (shown in phan 76 about the fixed pivot pin 74 when the tom) of the aircraft structure in which the in handle is closed or down or when the latch vention is mounted. In Fig. 3 it can also be hook 50 is secured, under load, with the 80 seen that the primary load line L of the as keeper 53. In the preferred embodiment the sembly is defined by a plane which passes mechanism is a rigid impeding element 90 through the center of the keeper 53 and the which is positioned intermediate the latch center of the mounting bushing 74. The pivot hook 50 and the handle 20. The impeding pin 76 by which the latch hook 50 is primarily element 90 has a first or forward portion 91 85 secured to the link mechanism 70 lies in an and a second or rearward portion 92 formed area above, or overcenter with respect to the integral to the first portion. The forward por- load line. Any additional tension load applied tion 91 includes a leading or forwardmost end along the latch load line will tend to close the edge 93 which may have an arcuate shape as latch, accordingly the latch is termed overcen- shown. It should be noted that the latch hook 90 ter. Notice also in Fig. 3 that the leading edge rearwardly extending arms 55, 56 are con- 93 of the impeding element bears on the sur nected by a wall surface 94. The impeding face 94 of the latch hook 50.

element forward portion 91 is of a size so as To open the handle 20, without releasing to fit, without interference, between the latch the hook member 50, a force F, is exerted hook arms 55, 56 with the leading edge 93 95 on the trigger 30 as shown in Fig. 4. A force bearing upon the wall surface 94 as will be sufficient to depress and thus overcome the described further hereinafter. biasing spring 36 is required to pivot the trig The rearward portion 92 of the impeding ger hook portion 35 away from the pin 73 element 90 includes a trailing edge 95 which and thus release the handle so that it may is provided with a curved surface also. An 100 freely rotate open either manually or by the area of the second portion 92 is provided biasing force of the spring 80.

with a through-hole 96 at a point distal from After the handle has rotated to a first or the leading edge 93 of the impeding element. open position the latch hook assembly will still The through-hole 96 is of a size so as to be under load with the keeper assembly as accommodate the passage and contain therein 105 shown in Figs. 5 and 7. It should be noted the pivot pin 78. In the preferred embodiment that at this point the impeding element 90 is a bushing-type extension 97 is provided on no longer contacting the latch hook 50, but one-side 98 of the impeding element and sur- instead has moved rearwardly with the handle rounds the through-hole 96. This extension 97 20. The handle opens approximately ninety is provided for stabilizing the location of the 110 degrees, unlike handles of prior art latches impeding element on the pivot pin 78. The which generally open no more than fifteen de continuous but different shaped surfaces of grees. At this time the assembly may be in the impeding element are provided to insure spected, adjusted or otherwise attended to clearance with respect to the other operating without requiring release of the hook member structure surrounding the impeding element 115 from the keeper 53. In Fig. 5 it can be seen when assembled as shown in Fig. 3. that the pin 78 is positioned in the rearward As can now be appreciated the free end 85 end 4013, 42B of the slots 40, 42 when the of the spring 80 fits over the top edge 99 of handle is in this first position.

the impeding element 90 and grasps the ele- To release the latch hook 50 from the ment along the side wall 98. Thus the imped- 120 keeper assembly 53, the operator must index ing element 96 is biased by the spring 80 the handle into a second position from that such that the movement of the impeding ele- which is shown in Fig. 5, in order to cause ment 90 is directly affected by movement of the link 70, and hence the latch hook 50, to the handle 20 which is also biased by the move forward when the handle 20 is rotated.

spring 80. It should be noted that other em- 125 To index the handle into the second position bodiments for the invention may require the the operator exerts a force, F3, on the handle use of a spring separate from that which is 20 in a direction towards the link mechanism used to bias the handle as does the spring 80 second end 25. The force F3 must be suffici in the preferred embodiment. ent to overcome the biasing force of the Referring now to Figs. 2-14, the preferred 130 spring 80 and move the handle such that the 4 GB2189539A 4 pin 78 is displaced with respect to the slots, to bring the latch hook 50 forward with the i.e. from its initial position into a second posi- handle 20. Indexing of the handle, as was tion at the forward ends 40A, 42A of the required for the release of the latch hook 50, slots 40, 42. When this occurs, the pin 46 is not necessary for the re- latching of the as moves downwardly and is positioned for cap- 70 sembly. When the latch hook 50 is again po ture by the detents 79 on the links 70A, 70B. sitioned forward of the keeper 53 as shown See Fig. 7. in Fig. 12, the handle is then rotated in a After the indexing has been accomplished rearward direction by a force F, causing the and while the handle is being maintained in its hook member to engage the keeper. The pivot second position by a force F. the handle is 75 76 is moved rearwardly and upward by the rotated as indicated by the arrow F, shown in handle movement until it passes over the cen Fig. 8. Because the pin 46 is captured by the ter or load line L. See Fig. 13. When this detents 79 and the pin 78 is positioned in the occurs the latch assembly is again secured by forward ends of the slots 40, 42, the handle its primary toggle locking mechanism as 20 is mechanically linked with the link mecha- 80 shown in Fig. 3. The handle may then be nism 70. Thus any forwardly directed force pushed forward, thereby automatically posi exerted upon the handle 20 will be transferred tioning the impeding element with respect to through the link mechanism 70 and hence to the latch hook. The handle and latch hook are the latch hook 50. The pivot pin 76 is thus thus locked by the secondary locking mecha- brought over the center or load-line L. The 85 nism, i.e. trigger 30, and the link mechanism hook member 50, as it moves forward as in- pin 73.

dicated by the arrow F, in Fig. 8, is released From the foregoing description of the con from the keeper assembly and is unlatched struction and operation of a preferred embodi allowing the operator to access the interior of ment, the benefits and advantages of the pre the aircraft structure. Note again the position 90 sent invention may now be understood. One of the impeding element 90 as it remains clear significant advantage is that the inadvertent re of the latch hook 50 to permit free movement lease of a latched hook member under vibra of the latch hook as it is being deliberately tion may now be prevented even in the event unlatched. of a failure of the secondary locking mecha- However, Fig. 9 illustrates that immediately 95 nism, e.g. a locking trigger as shown in this after the load on the latch hook 50 has been application. Essentially the impeding element released, the handle, as it continues to move of the invention, as constructed and posi forward under the forces F, and F, brings the tioned relative to the other parts of the latch impeding element surface 93 adjacent the assembly, bears upon the secured latch hook latch 50 into contact with the latch hook. The 100 and impedes or obstructs the latch hook from impeding element, in this particular application inadvertent reverse movement which, in the will thus exert a lifting force upon the released absence of the invention, may cause the latch latch hook 50 as the handle is continued in its hook to move out of its overcenter secure rotation about the pivot pins 74, 76 by the ment with respect to the load line. For operator. This arrangement thus assists the 105 example, in the event the trigger lock should operator with removal of the latch hook end fail or otherwise be released in mid-flight of portion 51 from capture by the keeper pin 53. the aircraft, the handle would open and be In the absence of the spring 80 biasing the subject to whatever airstream or vibrational impeding element 90, such assistance would forces are present in the environment. With not be available to the operator, and the oper- 110 prior art latch designs, such a failure of the ator would then have to manually lift the latch secondary locking mechanism in most circum hook 50 out and away from the keeper pin stances will also lead to the failure of the 53. primary locking mecha nism when the released When the latch hook 50 is released from handle is subject to uncontrolled wind or vi the keeper assembly, the handle rotation may 115 brational forces.

be reversed once again. In its unlatched posi- Another feature of the invention is the ease tion, the hook member 50 rests on the im- by which it may be used. The impeding ele peding element 90, clear of the keeper por- ment is controlled by the operator through tion, as shown in Fig. 10. The spring 80 re- normal handle rotation. No additional manual turns the handle to its first position with the 120 movement of the assembly is required by the pin 46 free from capture by the link detents operator with respect to the spring-biased im 79. The pin 78 is returned to a position at peding element.

the rearward ends of the slots 40, 42 once Still another important feature of the inven again. tion is the added safety it provides an opera- To re-latch the hook assembly with the 125 tor when the operator is improperly closing a keeper assembly the operator need merely ro- latch assembly which is under load, e.g. when tate the handle forward as shown in Fig. 11. the operator is blocking the free movement of The pivot connections made possible via pins the trigger while simultaneously pressing upon 78 and 76 as well as the impeding element the handle to close it. Fig. 14 illustrates this 90 bearing upon the latch hook, are sufficient 130situation.

GB2189539A 5 With reference to Fig. 14, when re-latching pivot point, the link mechanism permitting ro- the latch assembly subsequent to the step tational movement of the second pivot point shown in Fig. 13, the operator may exert a about the fixed pivot point, the second pivot closing force not only upon the handle as point being overcenter relative to the fixed pi noted by F, but also upon the forward end of 70 vot point to provide a primary locking mecha the trigger 30 as noted by F8. If the force F. nism when the latch hook is secured relative is allowed to remain, the trigger 30 will not to the keeper, wherein the improvement com function properly in that the force F, prevents prises:

the trigger 30 from rotating so that the hook means for preventing rotation of the link portion 33 is captured by the pin 73. Hence, 75 mechanism, the hook, and the second pivot the secondary lock does not lock. Instead, the point about the fixed pivot point when the closing force F. as transferred to the trigger latch hook is secured relative to the keeper hook portion 32 bearing upon the pin 73 may and forces are applied to the secured latch be sufficient to cause the link mechanism 70 assembly tending to release the assembly to be leveraged downwardly and pivot about 80 from an overcenter primary locked position, the pin 73. Such may cause the assembly to said rotation preventing means being con be moved out of its primary, locked overcen- structed and arranged to counteract such ter position. However, with the use of the forces and thereby provide a supplemental present invention such a malfunctioning is pre- locking mechanism.

vented in that Fig. 14 illustrates that the im- 85 2. The overcenter tension latch assembly peding element surface 93 is continuously of claim 1, wherein said rotation preventing bearing against the latch hook 50 as the clos- means includes an impeding element, posi ing forces F7, F. are being exerted upon the tioned intermediate the handle and the latch handle. Accordingly, the impeding element will hook, and constructed and arranged to engage exert a force against the latch hook 50 which 90 a portion of the latch hook at a point interme will counteract any rotational force upon the diate the fixed pivot point and the second pi link mechanism which is caused by the im- vot point.

proper functioning of the trigger lock 30. 3. The overcenter tension latch assembly Thus, the impeding element impedes or pre- of claim 2, said impeding element having a vents the link mechanism, latch hook and 95 rigid construction including a first portion hav hence the second pivot point or pivot pin 76 ing an arcuate end edge for engaging a por from rotating about the fixed pivot point or tion of the latch hook during closure of the pivot pin 74. latch assembly handle and a second portion Finally, the embodiment described indicates rotatably mounted with the handle and the link how the invention provides industry with a 100 mechanism.

flexibility in designing of such tension latch 4. The overcenter tension latch assembly assemblies which has heretofore not been of claim 3 wherein said impeding element is available. Because the impeding element funcrotatably mounted with the handle and the link tions as it does as a supplemental locking at a point distal from said impeding element mechanism, various other design restrictions 105 arcuate end edge.

which have been required to offset latch mal- 5. The overcenter tension latch assembly functioning can optionally be eliminated. This of any of claims 2 to 4 wherein said rotation will then free the designers of such latch preventing means further includes spring mechanisms from burdensome design restric- means for biasing said impeding element tions and provide the customer with latch de- 110 against the latch hook portion as the handle is signs which are more specifically suited for being closed.

the customers particular application. One such 6. An overcenter tension latch assembly design restriction which may be eliminated is substantially as herein described with refer that which calls for the top surface 54 of the ence to the accompanying drawings.

latch hook 50 to be in as near close abutment Printed for Her Majesty's Stationery Office with the adjacent underside of the latch handle by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987.

as possible. This design restriction is often Published at The Patent Office, 25 Southampton Buildings, required in prior art latch designs in order to London, WC2A 1 AY, from which copies may be obtained.

prevent the latch from inadvertently going out- of-toggle as a result of severe vibrational forces acting upon the assembly when under load.

Claims (1)

1. An overcenter tension latch assembly having a handle, a latch hook, a keeper for the latch hook, a fixed pivot point, a second pivot point rotatable about the fixed pivot po int, and a link mechanism engaging the handle and connecting the latch hook with the fixed