with reference now to fig1 and 2 , there is shown an exemplary embodiment of a retention and release mechanism 10 consistent with the invention . as shown , the mechanism generally includes a plate 12 , a release latch 14 disposed over a compression spring 16 , an upper arm linkage 18 housing a tension adjustment assembly 20 , a lower arm linkage 22 having a first end pivotably attached to an end of the upper aim linkage by a pivot pin 24 and a second end pivotably attached to a mounting bracket 26 by a pivot pin 30 , and a torsion spring 28 for creating a bias force tending to rotate the lower arm linkage 22 in an inward direction , i . e ., toward a ski boot as shown , for example , in fig5 . the tension adjustment assembly 20 generally includes a threaded release tension adjustment screw 32 , a corresponding tension adjustment nut 34 , a tension spring 36 , a retainer pin 38 and a stop 40 . the plate 12 is adapted to be affixed to a ski boot . those skilled in the art will recognize that there are a variety of means by which the plate 12 may be affixed to the boot . in the illustrated exemplary embodiment , however , the plate includes a first bore 50 on a tab 52 and a second bore 54 at an opposite end of the plate . the tab 52 may be bent at a 90 degree angle relative to the plate , e . g . at line 56 , and inserted into an opening ( not shown ) in the upper of the ski boot . the tab may be further bent to position the end of the tab and the bore 50 against the interior surface of the upper . fasteners ( not shown ) may be passed through the bores 50 , 54 and into the boot to secure the plate 12 thereto . the plate also includes a pair of spaced , opposed tabs 58 , 60 extending outward at a 90 - degree angle from the back surface 68 of the plate . the tabs 58 , 60 include aligned lock pin bores 62 , 64 therein for receiving opposite ends of a lock pin 66 . as will be described in detail below , the lock pin is dimensioned to be removably received within corresponding transverse slots 70 , 80 in the release latch 14 and upper linkage arm , respectively . the release latch 14 has a head portion 72 and a shaft portion 74 . with reference also to fig3 and 4 , the end of the shaft portion distal from the head is received within central opening 76 in the upper arm linkage 18 . as shown particularly in fig4 the compression spring 16 is positioned between a shelf 90 on the interior of the latch and an opposing shelf 92 on the interior of the upper arm linkage 18 . a pair of tabs 94 , 96 extends radially outward from the latch and into corresponding aligned slots , e . g . slot 98 formed in the sides of the upper arm linkage . the release latch is thereby captured within the upper arm linkage and biased outward from the linkage by the compression spring 16 . axial travel of the latch within the opening in the linkage arm 18 is limited by engagement of the tabs 94 , 96 with the ends of the slots , e . g . slot 98 . in an at rest position , the compression spring biases the tabs against the upper ends of the slots , and the transverse slot 70 in the latch extends into the opening in the upper linkage arm defined by the slot 80 therein , as shown , for example , in fig7 . in this position , the lock pin may be captured in the slots 70 , 80 by a lip 100 on the latch . the latch may , however , be depressed against the force of the spring 16 until the tabs contact the bottoms of the slots , and until the slot 70 aligns with the slot 80 to permit entry or exit of the lock pin 66 into the slots 70 , 80 . the upper arm linkage 18 provides a housing for the tension adjustment assembly 20 . with continued reference to fig4 the adjustment screw 32 has a head portion 102 , which extends through a bore in the shelf 92 . the head is secured within the bore with a radially extending flange 104 positioned against a bottom surface of the shelf 92 . the head is secured within the bore to prevent axial movement of the screw 32 , while allowing rotation of the screw . fig2 and 4 show alternative exemplary embodiments , i . e . 34 , 34 a , respectively , of the adjustment nut . the nut 34 in fig2 includes a head portion 106 that rests on a top of the compression spring 36 and a shaft portion 108 , which is adapted for extending into a central opening 110 of the compression spring . the nut 34 a , as shown in fig4 , has a simple flat construction . a bottom surface 112 of the nut 34 a rests on the top of the compression spring . in any embodiment , however , the nut includes a threaded bore for meshingly engaging the threads on a shaft 114 adjustment screw . the head 102 of the screw is exposed at the top surface of the shelf 92 to permit access to the head by a tool ( not shown ) extending through the opening 116 in the latch from the top thereof and through the central opening 118 of the spring 16 . the head is adapted to receive the tool so that the tool may be manipulated to rotate the head of the screw . for example , in the illustrated exemplary embodiment , the head includes a transverse slot 120 therein for receiving the end of a standard screwdriver . the end of the screwdriver may be passed through the top of the latch 14 and through the spring 16 to engage the slot 120 . rotation of the screw by the tool causes translation of the adjustment nut 34 , 34 a on the shaft 114 of the screw . the tension spring 36 is trapped between the bottom surface 112 of the nut 34 a ( or the bottom of the flange of the nut 34 in fig2 ) and the flange 122 on the retainer pin 38 . the retainer pin is fixed within the upper linkage arm 18 with a bottom surface the flange 122 disposed against the annular stop 40 , which is fixed around the pivot pin 24 . in the illustrated embodiment , the retainer pin includes a shaft portion 124 that extends into the central opening 110 of the spring to stabilize the spring and the pin within the upper linkage arm . as will be described in more detail below , with the spring trapped between the nut 34 a and the pin 38 , translation of the nut caused by rotation of the screw results in corresponding compression / relaxation of the compression spring depending on the direction of rotation . the upper linkage arm is pivotably connected to the lower linkage arm 22 by the pivot pin 24 extending through slots 126 , 128 in clevis plates 130 , 132 formed on the upper linkage arm and corresponding bores 134 , 136 in devises 138 , 140 formed on the lower linkage arm . the slots permit limited axial movement of the upper linkage arm relative to the lower linkage arm to facilitate pivotal movement the upper arm relative to the lower arm . the lower linkage arm includes a transverse bore 142 in the bottom portion thereof . the arm is pivotally secured to the mounting bracket 26 by the pivot pin 30 extending through the bore and corresponding aligned bores 144 , 146 in the mounting bracket 26 . bores 148 , 150 in the mounting bracket are provided to facilitate affixation of the bracket 26 to the ski boot by fasteners , e . g . screws , extending through the bores and into the boot . the torsion spring 28 is positioned around the pivot pin 30 and has a first end 152 captured by the lower linkage arm and a second end 153 captured the mounting bracket . the spring thereby biases the linkage arm for rotation about the pivot pin in a direction toward the boot . in this non - release position , as shown for example in fig1 and 4 , the bottom edge 156 of the upper linkage arm is positioned adjacent the upper edge 160 of the lower linkage arm at a point which is offset from the axis of the pin 24 . in a release position rotation ( i . e ., in a direction toward the boot ) of the upper arm 18 relative to the lower arm 22 is limited by contact of the rear surface 162 of the upper arm against the contact points , e . g . point 164 , on both sides of the lower linkage arm , as shown , for example , in fig6 . this limit may also be obtained by interference of the boot upper with the lower portion , or by means of a dash pot or stop ( s ) that coacts with the one or more parts of the retention and release mechanism or another portion of the boot upper . in any event , the secondary “ stop ” or arrest mechanism should limit rearward travel of the upper to less than approximately 20 degrees rearward from vertical . the operation of an exemplary release and retention mechanism consistent with the invention , along with additional structural features , will now be described . with reference also to fig5 - 7 , the plate 12 is secured to the rigid upper 200 of the ski boot 202 , while the mounting bracket 26 is secured to the lower portion 204 of the boot . in the “ ski ” position , as shown in fig5 the locking pin 66 is disposed within the slot 70 in the latch and the slot 80 of the upper linkage arm . the lip 100 on the latch extends upward at the front of the slot 70 . the compression spring 16 biases the latch against the locking pin 66 and the lip prevents removal of the pin 66 from the slots 70 , 80 absent depression of the latch 14 by a user . with the mechanism in “ ski ” position , the lower linkage arm 22 is biased toward the boot 202 by the torsion spring 28 . with reference also to fig8 a , the tension spring 36 biases the upper linkage arm against pivot pin 24 into the bottom 127 of the slot 126 - 128 . in this position , the axes 17 , 19 of the two linkages are not aligned , and the linkages contact the contact point a between the end 156 and the edge 160 . the engagement of the locking pin with the release mechanism provides a rigid structure that resists rearward rotation of the upper 200 relative to the lower portion 204 of the boot about the pivot point 206 . the level of resistance before releasing against rearward rotation of the upper 202 is adjustable through the tension adjustment assembly 20 to provide a suitable level of resistance for a particular user , e . g . depending on the user &# 39 ; s physical characteristics and skiing style . a tool may be passed through the top of the latch to rotate the adjustment screw , as described above . in one direction of rotation , the rotation of the screw causes axial motion of the nut 34 a tending to compress the spring 36 and increase the resistance to rearward rotation by increasing the force against the lower linkage arm 22 through the pivot pin 24 . in an opposite direction of rotation , the nut translates in an opposite direction to relax the spring 36 and decrease the resistance to rearward rotation of the upper 202 . the level of releasing resistance established by the tension adjustment assembly may be indicated on a visual tension indicator 208 . as shown , for example , in fig2 the indicator may mount on a front of the upper linkage arm , and may have a slot 210 that aligns with a corresponding slot 212 in the linkage arm . the position of the top of the adjustment nut , e . g . nut 34 , may be observed through the slots 210 and compared against a scale ( not shown ) provided on the face of the tension indicator 208 . an appropriate level of resistance / tension based on the scale may be recommended for a particular user . with the mechanism in the “ ski ” position , as shown in fig5 a user may ski normally with the upper and the lower portion of the boot in a stable relationship to each other and the user . in the event of a rearward fall , however , the user would lean back in the boots , generating a rearward rotational force on the upper relative to the pivot point 206 . advantageously , this force would transfer to the mechanism 10 and would overcome the resistance provided by the tension adjustment assembly 20 and the bias force of the torsion spring . during the rearward rotation of the upper 202 , the force f causes downward travel of the upper linkage arm 18 in a direction of force f with the pivot pin 24 travelling toward the top 129 of the slots 126 - 128 . during travel , the two linkages rotate in a direction away from the boot around the point of contact a between the end 154 and the edge 160 . at the predetermined level set by appropriate adjustment of the tension spring , as illustrated in fig8 b , the axes 17 , 19 of the two linkages are aligned and the end 156 and the upper edge 160 contact at point a , which is offset by a distance d from the axis 23 ( fig3 ) of the pivot pin 24 . at this point , with only an incremental increase in the force f , the upper linkage 18 travels downwardly , and , due to the offset point of contact a from axis 23 , creates a component p of force which urges the mechanism to open toward the release position , as illustrated in fig8 c . in another exemplary embodiment of the invention , the two linkages may be already aligned in the rest position , as illustrated in fig9 . in this embodiment , the two linkages are not in contact from the beginning . during rearward rotation of the upper 202 , the upper linkage arm travels downwardly . at the predetermined level of force , the two linkage arms come in contact at the point a , as illustrated in fig8 b , and then open toward a release position as shown , for example , in fig8 c . the release and retention mechanism thus moves to the “ release ” position , in which the upper may be substantially vertically disposed , as shown , for example , in fig6 . the rearrangement of the upper and lower arm linkages in this manner allows the upper to rotate rearwardly until travel is arrested by contact of the rear surface of the upper link arm 162 against the contact points 164 of the lower link arm . this arrest may occur , for example , when the angle θ between the upper and lower linkage arms reaches approximately 90 degrees to correspond to rotation of the upper of approximately 20 degrees rearward from the vertical “ ski ” position . when the skier recovers from the fall and is able to rotate the upper forward again , the upper and lower arm linkages will rearrange into the stable “ ski ” position with the assistance of the torsion spring 28 . another advantageous feature of a retention and release mechanism consistent with the invention is illustrated in fig7 wherein the mechanism is illustrated in “ walk ” position . it is well known that normal walking motion is severely restricted by prior art boot designs wherein the upper 200 is rigidly fixed relative to the lower portion 204 of the boot . according to the present invention , however , a user may release the latch 14 from the locking pin 66 by depressing the latch and rotating the mechanism rearwardly away from the locking pin . in this “ walk ” position , the retention and release mechanism is disconnected from the upper , thereby allowing rearward rotation of the upper during walking to allow a more natural waking motion . in the “ walk ” position , the torsion spring 28 biases the mechanism toward the boot to prevent undesired motion of the mechanism relative to the boot , and the lip 100 prevents inadvertent engagement of the latch with the pin 66 . when the user desires to continue skiing , the mechanism may be returned to the “ ski ” position simply by depressing the latch 14 to allow entry of the locking pin into the slots 70 , 80 , and then releasing the latch to capture the locking pin . thus , according to the present invention there is provided a release and retention mechanism which , in a “ ski ” position , provides a stable relationship between a user and the upper and lower portions of a ski boot . when the user falls rearward , however , the mechanism releases to a “ release ” position at predetermined level of rearward force as established by the user through a tension adjustment assembly . in the “ release ” position the upper is allowed limited rearward rotation , thereby significantly reducing damaging forces on the knee joint and the likelihood of injury to the anterior cruciate ligament . when the user recovers control after the fall the user rotates the upper forwardly to return the mechanism to the “ ski ” position . alternatively , if the skier cannot recover control after the mechanism is forced into the “ release ” position , the mechanism has the effect of shortening the effective moment arm of the ski tail to the knee , thereby increasing the likelihood that the skier will fall over the tail of the ski without damaging knee ligaments . the invention , therefore , functions to absorb potentially injurious forces before the forces are sustained by the wearer &# 39 ; s knee joint . the embodiments described herein are but some of the several which utilize this invention and are set forth here by way of illustration but not of limitation . for example , a latch consistent with the invention may take a variety of forms , and may be permanently or releasably securable to the boot , either directly or through other elements such as a locking pin . also , the orientation of a mechanism consistent with the invention relative to the upper and lower portions of the boot could be reversed . it is obvious that many other embodiments , which will be readily apparent to those skilled in the art , may be made without departing materially from the spirit and scope of the invention as defined in the appended claims .
a retention and release mechanism and ski boot for mitigating injury to a skier when the rearward loads , potentially injurious to the user , are imparted to the boot . the mechanism includes a first linkage arm , a latch , and a second linkage arm . the latch is connected to a first end of the first linkage arm , and is configured for direct or indirect pivotal connection to a first portion of the boot , which is pivotally connected to a second portion of the boot . the second linkage arm is pivotally connected to a second end of the first linkage arm at a pivot point , and is configured for pivotal connection to the second portion of the boot . the mechanism provides stable orientation of the first portion to the second portion in a “ ski ” position , and allows rotation of the first portion relative to the second portion in a “ release ” position , the “ release ” position being established upon imposition of a predetermined level of rearward force on the boot . a tension adjustment assembly allows for adjustment of the predetermined level of rearward force . the latch may be releasable from the boot to allow rotation of the first and second boot portions relative to each other for facilitating a relatively normal waking motion .