US3121580A

US3121580A - Vehicle door latch mechanism

Info

Publication number: US3121580A
Application number: US116003A
Authority: US
Inventors: Salvo Anthony J Di; Maurice M Westerdale
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1961-06-09
Filing date: 1961-06-09
Publication date: 1964-02-18
Anticipated expiration: 1981-02-18

Description

Feb. 18, 1964 A. J. D! SALVO ETAL 3,121,580

VEHICLE DOOR LATCH MECHANISM Filed June 9, 1961 2 Sheets-Sheet 1 AN THON) J DIS/4L v0 MAURICE M. WES TERDAL E INVENTORS BY M A TTOE'NE'VS 1964 A. J. DI SALVO ETAL 3,121,580

VEHICLE DOOR LATCH MECHANISM Filed June 9, 1961 2 Sheets-Sheet 2 NA 39 49 47 F/G4 A N THON) J 01.54 L V0 MAUR/C E M. WES TE RDAL E IN VENTORS BY Q/ wl United States Patent 3,121,589 VEHECLE DGQR LATQE MECHANISM Anthony 5. Bi alvo, Allen lark, and Maurice M. Westerdale, ln' ter, Mich., assignors to Ford Motor Company, Dearhorn, Mini 1., a corporation of Delaware Filed June 9, 1961', filer. No. 116,0(l3 5 Ciaiins. (Cl. 292-229) This invention relates to latch mechanisms for swinging doors, especially the doors of automobile or other vehicle bodies.

Most door latch mechanisms currently in use on passenger motor vehicles comprise a rotatable or pivotable latch device adapted to en age a striker or keeper device mounted on a vehicle door framing structure, a detent means releasably engaged with the latch device to hold the latter in door latched position, an actuating or release lever operatively associated with the detent means for disengaging the same from the latch device, and manually operable means accessible from the outside and inside of the vehicle door operative to cause disengagement of the detent means. In almost all latch mechanisms of this general class, the manually operable means operative from the outside of the door acts on the detent means through the actuating or release lever. The manually operable means operative from the inside of the door may be constructed and arranged to act directly on the detent means or through the actuating or release lever, depending on whether or not it is desired to have a latch mechanism which cannot be rendered inoperative from the inside of the vehicle. Most vehicles are provided with at least one door which can always be opened from the inside of the passenger compartment even if the latch mechanism is conditioned so that the door cannot be opened from the outside.

Latch mechanisms may be categorized by the manner in which the manually operable means is rendered inoperative to disengage the detent means from the latch device to place the latch mechanism in locked condition. This may be done by the use of a blocking means selectively positionable to block movement of the detent means actuating or release lever. This may also be done by use of a disconnection means interposed in the train of members extending from the manually operable means to the detent means.

Reference may be made to US. Patent No. 2,987,336, issued June 6, 1961, for a latch mechanism exemplifying the type in which a blocking means is used to render the manually operable means inoperative to disengage the detent means from the latch device.

it is an object of the present invention to provide a latch mechanism characterized by many of the features of the latch mechanism disclosed in the above-mentioned patent and which is further characterized by the inclusion of features by which the means manually operable from the outside of the door, such as the handle, push button or like operated means, may be operatively disconnected from the detent actuator or release lever.

More specifically, in the latch mechanism embodying the present invention, the train of parts or members operatively associating the handle, push button or the like to the detent means includes a part or member directly coupled to the detent means but being shiftable thereon from a detent actuating to a detent non-actuating position. This part or member is shiftable by a locking lever operable from either the outside or the inside, or both, of the door. A latch mechanism so constructed is said to have a free wheeling handle, push button or the like as distinguished from a blocked type. In other words, the handle, push button or the like is always responsive to finger pressure regardless of whether or not the latch Patented Feb. 18, 1964.-

in mechanism is in locked or unlocked condition, even though movement of the handle, push button or the like in locked condition of the latch mechanism is not effective to cause disengagement of the detent means from the latch device.

Probably the major advantage to be derived from socalled free wheeling type latch mechanisms is that the latch mechanism parts, particularly those in the train of elements between the outside operator and the detent means, may be made of much lighter gauge metal than the parts used in a blocked type lock. The reason is that in a blocked type lock, the parts must be made strong enough to withstand any force which might be exerted on the outside operator by means of a pry bar, hammer or other device which may be used when it is attempted to break or make a forceful entry through the door when the door is in locked condition. It will be readily apparent that in a latch mechanism where part of the train of elements is disconnected, any force exerted on the handle, push button or the like by an implement of any kind is ineiiective to distort or spring the latch mechanism parts to a degree sufficient to cause disengagement of the detent from the latch device so as to permit the door to be opened. This, of course, applies to any impact the handle, push button or the like might sustain in a collision or upset of the vehicle. The use of light gauge metal results in a cost saving in the manufacture of the latch mechanism. Less metal is used and the life of the die for stamping the parts is much longer with light gauge metal.

Other objects, advantages and features of the present invention will be made more apparent as this description proceeds, reference being had to the accompanying drawings, wherein:

FIG. 1 is an elevational view of the latch mechanism as it appears from the inside of the vehicle door;

FIG. 2 is a fragmentary view in part similar to P16. 1 illustrating parts of the latch mechanism in an operative position different from that shown in FIG. 1;

FIG. 3 is an elevational view in part sectional taken from the right side of FIG. 1; and

FIG. 4 is an enlarged sectional view taken on the line 4-4 of FIG. 1.

In the drawings there is illustrated, by way of example, a preferred embodiment of the present invention as applied to the doors and door frame structures of an automobile body. Adapted to be secured as by means of screws (not shown), to the inner side of the free edge wall of a vehicle door is a case plate 31 having a flange 12 which is adapted to be positioned along the inner panel of the door. The present latch mechanism has a pair of pivoted latch devices comprising jaw elements 13 (see FIG. 3) positioned at the outer face of the case plate 11. As best seen in FIG. 3, each jaw element 13 is provided with an integral stud or pivot shaft 14 having a reduced bearing portion 16 extending through an aperture in the case plate, the aperture having a flanged edge 17 providing bearing support for the bearing portion -16. In FIG. 3, a Washer 18 is shown interposed between the case plate 1'1 and the main body portion of the stud shaft 1d. The inner reduced end or bearing portion 16 of the stud shaft is provided with longitudinally extending fiats 19 thereon. Fitted over the reduced end or bearing portion 16 and keyed thereto by the flats 19 are a pair of

control plates

21 and 22, respectively. From the foregoing, it is apparent that each jaw element 13 is rigid'iy coupled to a control piste 2.1 and 22, respectively, being concentric therewith on a stud shaft 1.4. As defined herein, each latch device thus comprises a jaw element '13, a stud shaft or pivot 14 and a respective control plate ill or 22.

Each jaw element 13 is a substantially triangular plate member having its pivot axis located near the apex end. The base or side 23 opposite the apex end is outwardly rounded and is provided in the center thereof with a semicircular recess or enlarged notch 24.

Each control plate is a gear sector having teeth 26, the teeth being intermeshed to thereby couple the control plates together for correlated movement. Thus, both jaw elements 13 are controlled for movement in unison in counterdirections of swinging movement toward and from each other into and out of door latched condition. A spiral spring 27 is disposed substantially coaxially or concentric with and adjacent the inner face of the control plate 21. The spring 27 has its inner end 28 operatively connected to the stud shaft 14 carrying the control plate 21, the stud shaft having a diagonal slot or kerf 29 receiving the spring end. The outer or free end 31 of the spring 27 is looped over the edge of a notch 32 in the case plate flange 12. The spring 27 is installed in a wound up or preloaded condition so that at all times it tends to rotate control plate 21, shaft 14 and jaw element 113 associated therewith in a counterclockwise direction as viewed in FIG. 1. Since the control plate 22 is coupled to the control plate 21 through the gear teeth 25, rotative force exerted by the spring 27 on the plate 21 is transmitted to the plate 22 so that it, at all times, is under rotative force tending to rotate it, shaft 14 and jaw element 13 associated therewith in a clockwise direction as viewed in FIG. 1.

The control plate 22 is provided with two peripherally spaced abutments or ratchet teeth 33 and 34, respectively. Cooperable with the abutment or ratchet toothed edge of the control plate 22 is a swinging detent, pawl or dog 35 pivotally mounted on a shoulder rivet 36 secured to the case plate 11. It will be noted that the detent 35 extends in a substantially horizontal direction across the case plate 11 and is pivoted intermediate its ends. At one'side of the pivot axis, the right side as viewed in FIG. 1, the detent is provided with an abutment portion 3'7 extending in a substantially upward direction and cooperable with the teeth or abutments 33 and 34 on the control plate 22. When the detent abutment 37 is in engagement with the control plate abutment 33, the jaw elements 13 will be in a safety latched position. When the abutment .37 is in engagement with the latched control plate abutment 34, as shown in FIG. 1, the jaw elements l3 will be in final latched position, as will be more fully explained. To the right of its pivot axis 36, the detent 25 is provided with an extension 38 and to the left of its pivot axis it is provided with an enlarged stepped or embossed portion 39. The enlarged portion 39 of the detent has a substantially L-shaped slot 41 therein. The slot 41 has two sections, section 42 extending radially of the pivot axis 3% and section 43 extending upwardly from the irmer end of the section 42 and circumferentially relative to the pivot axis 36. Extending through the slot 41, is a stepped cylindrical bearing or bushing m mber, generally designated 44-. The bushing is preferably made of a low friction coefficient material, such as one of the nylon or Teflon plastics used for bearing or bushing devices. As best seen in FIG. 4, the bushing 4 lhas an enlarged head portion 45 at one end thereof and a smaller diameter cylindrical portion which slidably fits through the slot 41. On the end opposite the enlarged head portion 45 of the bushing, the cylindrical portion 4-6 is encompassed by one end 4-7 or" a link A Washer .9 is interposed between the inner surface of the link 47 and the surface of the detent portion 3%. The link end 47 is retained on the bushing by a shoulder 51. The bushing 44 has a longitudinally extending aperture 52 therethrough. At the end of the bushing opposite its head end, the aperture 52 is intersected by a semicircular recess 53 having lip portions 2- creating a restricted entrance to the recess.

The recess 5'3 and the longitudinally extending hole 52 are adapted to receive the L-shaped end 55 of a link or rod 56 connecting the bushing 4-4 to a bell crank lever 57 pivotally supported on a bracket 53 at the upper part of the vehicle door (not shown). The bracket 58 may be an integral part of a door handle assembly or otherwise mounted within the door. The lever 57 has a depending flange portion 59 which lies in the path of the plunger or stem till which forms an extension of a conventional push button mounted in a door handle accessible from the outside of the vehicle door.

Referring now to FIG. 2, the bushing 44 is illustrated as being at the extreme outer end of the radially extending section 52 of the slot 41 in the end 39 of the detent 35. Upon the door handle push button being depressed so that its stem 61 moves toward and engages the flange 59 on the bell crank lever 57, the bell crank lever 57 will be swung in a counterclockwise direction raising the link 57 and also the bushing 44. But since the bushing 44 is held against upward movement relative to the detent by its relationship to the slot section 42, the movement of the link 56 is transmitted to the detent 35 cansing the latter to be swung in a clockwise direction as viewed in the drawings. It will be readily apparent that this will cause the abutment 37 on the detent 35 to move out of the path of the abutments 34 and 33 on the latch control plate 22. This permits the spring 27 to urge the jaw elements toward unlatched condition and thereby permit-ting the vehicle door to be opened.

Referring now to P16. 1, it will be noted that the bushing is shown at the inner end of the section 42 of the slot 4d or in position to move in the circumferential sec tion 43 of the slot 41. Under this condition, upward movement of the link 56 through actuation of the bell crank lever 57 is eliective to raise the bushing 44. The latter, however, moves freely relative to the detent 35 and the latter is thereby maintained in a relationship such that its abutment 37 blocks movement of the control plate 22.

The position of the bushing 44 is controlled through a locking lever 62 pivotally mounted intermediate its ends on a pivot stud 63 secured to the case plate 11. At its left end, as viewed in the drawings, the locking lever 62 is provided with a stepped or embossed upwardly extending appendage 64. The above-mentioned link 48 is pivotally connected at its end 65 to the appendage 64. The locking lever 62 acting through the link 48 controls the position of the bushing 44 relative to the radially and ci-rcumfe-rentially extending sections 42 and 43, respec tively, of the slot 41 in the detent 35. As shown in FIG. 1, the left end of the blocking lever 62 is in a raised position and the link 48 has pulled the bushing 44 toward the right or into the circumferentially extending section 43 of the slot 41. Upon the locking lever being swung in a counterclockwise direction so that its left end is lowered, the link 48 will push the bushing 44 downwardly and into the extreme outer end of the section 42 of the slot 41, thus placing it in a position to transmit movement of the link 56 to the detent 35.

It will be noted that the detent 35 has a downwardly extending part 66 which is adapted to abut a projection 67 of the locking lever. This abutting relationship serves two functions: First, it provides a stop limiting the extent to which the locking lever may be swung in a counterclockwise direction. Further, when the latch control plate 22 is in its unlatched position, the surface 63 of the abutment 33 will overlie the corner of the abutment 37 on the dentent. This prevents the latter from moving into a fully latched position relative to the control plate 22. As a result, the portion 66 of the detent 35 will be positioned somewhat below its position shown in FIGS. 1 and 3 and will obstruct upward movement of the portion 67 of the locking lever 62. This prevents the latter from being swung so as to fully raise its appendage 64. The degree of movement is such that the bushing 44 will not come out of the section 42 of the slot 41, and the latch mechanism can thus not be placed in latch locked or free wheeling condition. The relationship of the parts is such 55 that the latch mechanism can only be placed in latched locked or free wheeling condition when the door is closed and the jaw elements fully encompass the striker or keeper device with which they coact to maintain the door in a latched condition.

The locking lever 62 is adapted to be swung from nonlocking position into locking position in a conventional manner either from the inside or the outside of the vehicle door. For actuation from the inside of the door, the end of the locking lever 62 to the right of the pivot axis 63 is provided with an aperture 69 therein to receive the end of a rod (not shown) provided with an access button (not shown) located on the inner side of the door panel in an accessible location. For actuation from the outside of the door, the locking lever 62 is provided at the other side of its pivot axis with a slotted flange 71 located bencath the appendage 6 This flange '71 is adapted to receive the crank end of a shaft (not shown) coupled to a conventional key operated mechanism accessible from the outside of the vehicle door in a manner well-known in the art.

The locking lever 62 is yieldably held and urged toward its limits of movement by means of a snap-over or toggle spring 72 of suitable strength attached at one end to the locking lever 62 and at its other end to the case plate 11. As was stated above, the limit of movement of the locking lever 62 in a clockwise direction is controlled by the abutment portion 66 of the detent 35. The movement of the locking lever in a counterclockwise direction is controlled by the position of the bearing 44 in the end portion of the slot section 42, the toggle spring thus being effective to ensure that the bushing 44 is urged fully to the left of the end section 42 of the slot as viewed in FIG. 2.

The present latch mechanism is preferably operated from the inside of the door through the medium of a remote control mechanism comprising a longitudinally shiftable drag link 73 which is pivotally connected to the lower end 74 of a bell crank lever 75 (see FIG. 3). The bell crank lever 75 is pivoted on the shank of a shoulder rivet 76 secured to the case plate flange 12. The bell crank lever 75 is provided with an angularly upwardly extending arm 77 adapted to overlie the extension 38 on the end of the detent means 35. Upon the bell crank lever being swung in a clockwise direction as viewed in FIG. 3, it will engage the extension end 38 of the detent 35 cansing the latter to be swung in a clockwise direction out of engagement with the ratchet teeth abutments 33 and 34. It should be noted that actuation of the detent 35 through the remote control bell crank lever '75 is independent of actuation by the outer manually operable means. Thus, even if the outside operator is rendered inoperative to disengage the detent from the latch device, the detent can always be disengaged from the latch device from the inside of the vehicle through actuation of the remote control mechanism.

The detent 35 is urged into latching engagement with the ratchet teeth abutments 33 and 34 by a coil spring "73 having its inner end held in a ker f or slot 79 in the pivot stud 36 mounting the detent 35 on the case plate 11. The spring 78 is provided with a horizontally extending free end portion 81 which overlies an edge of the step or embossment 39 in the detent. The free end portion 81 of the spring extends further so as to also overlie the path of upward movement of the bushing 44. The purpose of this is to ensure that the bushing 44 will not be frictionally caught in the upper end of the section 43 of the slot 4-1, but will always be urged toward the lower end of the section 43 of the slot. Thus, when the link 56 is raised with the bushing 44 in the free wheeling position, and the link is then released upon release of the push button extension 61 from hearing engagement with the flange h on the bell crank 57, the bushing will be restored to the intermediate position shown in FIG. 1 Where it is in position to be urged toward the section 42 of the slot 41 upon restoration of the locking lever to nonlocking position.

The manner in which the jaw elements 13 are adapted to coact with a striker or keeper device, generally designated 72, as seen in FIG. 3, is fully described in the abovementioned U.S. Patent 2,987,336. Accordingly, reference is made to that patent for these details.

It will be understood that the invention. is not to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A latch mechanism for a door comprising:

a support plate for disposition at a free edge wall of the door,

latch device means pivotally mounted on said support plate for movement between latched and unlatched positions,

a detent pivotally mounted on said support plate and having an abutment in engagement with an abutment on said latch device means for holding the same in door latched position,

an outer manually operable means including a first link means,

a bushing means coupling said first link means to said detent,

said bushing means projecting through a slot in said detent,

said slot having two sections,

one of said sections extending radially and the other of said sections extending circumferentially relative to the pivot axis of said detent, and

a locking lever pivotally mounted on said support plate,

a second link means coupling said locking lever to said bushing means,

said locking lever being operable through said second link means to move said bushing means from said radial to said circumferential section of said slot or vice versa,

said bushing means when positioned in said radial section being operative to transmit movement of said first link means occasioned by operation of said outer manually operable means to said detent to pivotally move the same to disengage said detent abutment from said latch device abutment and when in said circumferential section of said slot being freely movable with said first link means upon movement of the latter occasioned by operation of said outer manually operable means without causing movement of said detent.

2. A latch mechanism for a swinging door comprising:

a support plate for disposition at a free edge wall of the door,

latch device means pivotally mounted on said support plate for movement between latched and unlatchcd positions,

a detent pivotally mounted on said support plate for pivotal movement about a pivot axis parallel to the pivot axis of said latch device means and having at one side of its pivot axis an abutment in engagement with an abutment on said latch device means for holding the same in door latched position,

outer manually operable means including a first link means,

a bushing means coupling said first link. means to said detent,

said bushing means projecting through a slot in said detent at the opposite side of the pivot axis of the latter,

said slot having a first section which extends radially and a second section which extends circumierentiah ly relative to the pivot axis of said detent, and

a locking lever pivotally mounted on said support plate for pivotal movement about a pivot axis parallel to the pivot axes of said latch device means and detent,

s,121,sse

said detent being interposed between said latch device and locking lever,

a second link means coupling said locking lever to said bushing means,

said locking lever being operable through said second link means to move said bushing means from the radial to the circumferential section of said slot or vice versa,

said bushing means when positioned in the radial section being operative to transmit movement of said first link means occasioned by operation of said outer manually operable means to said detent to pivotally move the same to disengage said detent abutment from said latch device abutment and when in the circumferential section of said slot being free ly movable with said first link means upon movement of the latter occasioned by operation of said outer manually operable means Without causing movement of said detent.

3 A latch mechanism for a swinging door comprising:

a support plate for disposition at a free edge wall of the door,

a detent pivotally mounted on said support plate and having at one side of its pivot axis an abutment in engagement with an abutment on said latch device means for holding the same in door latched position,

outer manually operable means including a first link means,

a bushing means coupling said first link means to said detent,

said slot having two sections,

a locking lever pivotally mounted on said support plate,

the pivot axes of said latch device means, detent and locking lever being parallel and said detent being interposed between said latch device means and said locking lever,

a second link means coupling said locking lever to said bushing means,

said bushing means when positioned in said radial section being operative to transmit movement of said first link means occasioned by operation of said outer manually operable means to said detent to pivotally move the same to disengage said detent abutment from said latch device abutment and when in said circumferential section of said slot being freely movable with said first link means upon movement of the latter occasioned by operation of said outer manually operable means without causing movement of said detent,

said latch device means when in unlatched position abutting said detent and displacing the latter into a locking lever blocking position and preventing movement of said bushing to said circumferential section of said slot.

4. A latch mechanism for a swinging door comprising,

a support having a main plate portion for disposition at the free edge wall of the door,

a pair of jaw elements pivotally mounted on one side of said plate portion for swinging movement about spaced axes perpendicular to the plane thereof,

a pair of control members mounted on the opposite side of said plate portion,

each control member being fixedly coupled to one of said jaw elements for pivotal movement th rewith,

said control members having intermeshed portions whereby said jaw elements are controlled for movement in unison toward and from each other to door latched and door unlatched positions, respectively,

at least one of said control members being provided with a detent en ageable portion,

a detent pivotally mounted on said support plate and having at one side of its pivot axis an abutment engageable wtih said detent engageaole portion for holding said jaw elements in door latched position,

outer manually operable means mounted on said support,

said outer manually operable means including a first link means,

a bushing means coupling said first link means to said detent,

said slot having a first section extending radially and a second section extending circumferentially relative to said detent pivot axis, and

the pivot axes of said control member, detent and locking lever being parallel and said detent being interposed between said one control member and said locking lever,

a second link means coupling said locking lever to said bushing means,

said bushin means when positioned in said radial sec tion being operative to transmit movement of said first link means occasioned by operation of said outer manually operable means to said detent to pivotally move the same to disengage said detent abutment from said detent engageable portion of said one control member and when in said circumferential section of said slot being freely movable with said first link means upon movement of the latter occasioned by operation of said outer manually means without causing movement of said detent,

said latch device means when in unlatcbed position abutting said detent and displacing the latter into a locking lever blocking position and preventing movement of said bushing to said circumferential section of said slot.

5. A latch mechanism for a swinging door comprising,

a pair of control members mounted on the opposite side of said plate portion,

each control member being fixedly coupled to one of said jaw elements for pivotal movement therewith,

at least one of said control members being provided with a detent engageable portion,

a detent pivotally mounted on said support plate and having at one side of its pivot axis an abutment engageable with said detent engageable portion for holding said jaw elements in door latched position,

outer manually operable means mounted on said support, said outer manually operable means including a first link means,

a bushing means coupling said first link means to said detent,

said link means having an end portion passing through the center of said bushing means,

a second link means coupling said locking lever to said bushing means,

said second link means comprising a link which at one end thereof circumferentially encompasses said bushing means and which at the other end thereof is pivotally connected to said locking lever,

said locking lever being operable through said second link means to move said bushing means from said radial to said circumferential section or" said slot or vice versa,

said bushing means when positioned in said radial scction being operative to transmit movement of said first link means occasioned by operation of said outer manually operable means to said detent to pivotally move the same to disengage said detent abutment from said detent engageable portion of said one control member and when in said circumferential section of said slot being freely movable With said first link means upon movement of the latter occasioned by operation of said outer manually operable means Without causing movement of said detent,

References Cited in the file of this patent UNITED STATES PATENTS 2,236,702 Andersen Apr. 1, 1941 2,782,062 Smith Feb. 19, 1957 2,903,285 Roethel Sept. 8, 1959 2,987,336 Kramer June 6, 1961

Claims

1. A LATCH MECHANISM FOR A DOOR COMPRISING: A SUPPORT PLATE FOR DISPOSITION AT A FREE EDGE WALL OF THE DOOR, LATCH DEVICE MEANS PIVOTALLY MOUNTED ON SAID SUPPORT PLATE FOR MOVEMENT BETWEEN LATCHED AND UNLATCHED POSITIONS, A DETENT PIVOTALLY MOUNTED ON SAID SUPPORT PLATE AND HAVING AN ABUTMENT IN ENGAGEMENT WITH AN ABUTMENT ON SAID LATCH DEVICE MEANS FOR HOLDING THE SAME IN DOOR LATCHED POSITION, AN OUTER MANUALLY OPERABLE MEANS INCLUDING A FIRST LINK MEANS, A BUSHING MEANS COUPLING SAID FIRST LINK MEANS TO SAID DETENT, SAID BUSHING MEANS PROJECTING THROUGH A SLOT IN SAID DETENT, SAID SLOT HAVING TWO SECTIONS, ONE OF SAID SECTIONS EXTENDING RADIALLY AND THE OTHER OF SAID SECTIONS EXTENDING CIRCUMFERENTIALLY RELATIVE TO THE PIVOT AXIS OF SAID DETENT, AND A LOCKING LEVER PIVOTALLY MOUNTED ON SAID SUPPORT PLATE, A SECOND LINK MEANS COUPLING SAID LOCKING LEVER TO SAID BUSHING MEANS, SAID LOCKING LEVER BEING OPERABLE THROUGH SAID SECOND LINK MEANS TO MOVE SAID BUSHING MEANS FROM SAID RADIAL TO SAID CIRCUMFERENTIAL SECTION OF SAID SLOT OR VICE VERSA, SAID BUSHING MEANS WHEN POSITIONED IN SAID RADIAL SECTION BEING OPERATIVE TO TRANSMIT MOVEMENT OF SAID FIRST LINK MEANS OCCASIONED BY OPERATION OF SAID OUTER MANUALLY OPERABLE MEANS TO SAID DETENT TO PIVOTALLY MOVE THE SAME TO DISENGAGE SAID DETENT ABUTMENT FROM SAID LATCH DEVICE ABUTMENT AND WHEN IN SAID CIRCUMFERENTIAL SECTION OF SAID SLOT BEING FREELY MOVABLE WITH SAID FIRST LINK MEANS UPON MOVEMENT OF THE LATTER OCCASIONED BY OPERATION OF SAID OUTER MANUALLY OPERABLE MEANS WITHOUT CAUSING MOVEMENT OF SAID DETENT.