Abstract:
A mechanical fuse is used with ergonomic devices for seats such as automobile seats to allow the ergonomic devices to tolerate abusive loads without breaking a linkage, such as a traction cable, used to move the ergonomic supports. The traction cable is comprised of a sleeve with a wire disposed to slide axially through the sleeve. The mechanical fuse is installed with the sleeve divided into two sections, with an end of each section seated into a male component or a female component of the mechanical fuse. The male and female components of the mechanical fuse slide axially relative to one another but are restrained from sliding by insertion of a boss on one component into a detent on the other component. The boss and detent hold the male and female components together in a friction fit that resists axial movement. When an abusive force is applied to the fuse, the friction fit of the boss and detent is overcome so that the boss slides out of the detent in a radial direction. Once released, the male and female components slide axially into one another, shortening the overall distance of the traction cable sleeve until the abusive load is released so that the traction cable sleeves can resume their originally selected relative spacing. The friction fit is maintained by the compressive biasing of an external spring. The compressive force is resisted, and the fuse is reset, by the expansive force of an internal spring.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   None. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   APPENDIX 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to ergonomic supports for seats, especially automobile seats. 
   2. Related Art 
   A certain percentage of seats, especially automobile seats, will be subject to abusive loads in the course of their useful life. Abusive loads may be caused by light or heavy automobile accidents, misuse by the seat occupant, sudden, violent or unexpected movement by the seat occupant or the placing of overweight items on the seat. A wide variety of moveable components are installed in seats to provide ergonomic support for the occupants of those seats. By way of example, U.S. Pat. No. 6,536,840 B1 to Schuster is incorporated by reference herein. Because such ergonomic supports are typically mass produced, production costs are often controlled by manufacturers by using the least expensive, and usually therefore the lightest, component adequate to meet expected design loads, such as the ordinary weight of a seated passenger. Ergonomic supports constructed of components that are sufficiently heavy to tolerate abusive loads as well as ordinary loads are disadvantageously expensive. There is a need in the art for a system to protect the ergonomic support from damage caused by overloads while maintaining the ability to manufacture the ergonomic support from economical components. 
   By and large, ergonomic supports in seats move. Movement is usually achieved by an actuator such as a hand crank or an electrical motor, which is connected to the moving parts of the ergonomic support via a linkage. The linkage may be made of rigid components such as rods, spokes or hard drawn wire. More frequently, however, the linkage takes the form of a traction cable called a Bowden cable. The bowden cable is comprised of a sleeve or conduit with a wire disposed to slide axially through the sleeve. One end of the bowden cable is attached to an actuator, and the other end is attached to the ergonomic support, such as a lumbar support. The actuator moves the wire relative to the sleeve, usually by pulling the wire out from the sleeve. An example of an actuator is found in U.S. Pat. No. 5,638,722 to Klingler which is incorporated by reference herein. The relative movement of the sleeve and wire on one end obviously moves the other end of the wire relative to the other end of the sleeve. Accordingly, one part of a moving lumbar support is attached to the end of the wire, and another part of the ergonomic support&#39;s moving parts is attached to the end of the sleeve. For example, some lumbar supports are comprised of a flexible arching panel mounted on rails. The traction cable sleeve is attached to either the top or the bottom of the panel, and the wire is attached to the other end. Thus, when the actuator pulls the wire through the sleeve, the two ends of the panel are pulled together and it arches outwards towards the seat occupant, providing an arched lumbar support for the occupant. 
   In the case of ergonomic supports comprised of moving components that are actuated by a traction cable, the linkage of the cable components to the moving parts is likely to be damaged in the event an abusive load is placed on the components. Accordingly, there is a particular need in the art for a system capable of being assembled with a traction cable linkage that protects components from damage from abusive loads. 
   SUMMARY OF THE INVENTION 
   The present invention is a system method and apparatus for protecting ergonomic supports for seats from abusive loads. The present system, which may be referred to as a “mechanical fuse,” is designed to be installed in series with a traction cable, rigid rod or other type of actuation linkage. 
   The device of the present invention is comprised of a first cylindrical component engaged with a second cylindrical component, and in axially sliding communication with it. A first one of the cylindrical components engages a first portion of a traction cable sleeve. The other one of the cylindrical components engages a second portion of a traction cable sleeve. Alternatively, one of the cylindrical components may engage the structure of the lumbar system or the actuator. In another alternative, both cylinders may engage rigid rods. 
   The sliding axial communication of the first and second cylindrical components is designed to retain the relative axial position of the two components relative to one another through a certain preconfigured range of axial load. The cylindrical components slide axially relative to one another in the event that the axial load increases to a level greater than a preconfigured threshold. The traction cable wire proceeds axially through both cylindrical components. 
   Accordingly, when an abusive load is put on the ergonomic support, that load is transferred to the traction cable. The mechanical fuse of the present invention absorbs the abusive load by releasing the added tension on the traction cable sleeve when it lengthens the relative distance between the sleeve end and the wire end or shortens the distance between the cable sleeves (or rods) by allowing the cylindrical components to slide axially over one another. 
   The mechanical fuse of the present invention resets to re-establish the length and tension adjustment of the traction cable maintained before the abusive load occurred with an internal expansion spring. When an abusive load compresses the cylindrical components relative to one another along the axis of the traction cable, the expansion spring within them is also compressed. When the abusive load is released, the expansion spring pushes the cylindrical components back apart, returning them to their original position. 
   The engagement of the two cylindrical components may be with any of a variety of bosses and detents, tabls and slots or, in one embodiment, a sectioned collar and interrupted annular groove engagement. The collar and annular groove have cooperating faces held together by integral bias and, optionally, with a compression spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  is an illustration of a lumbar support actuated by a traction cable and including the mechanical fuse of the present invention. 
       FIG. 2  is a cross-section of the mechanical fuse of the present invention. 
       FIG. 3  is a perspective view of the mechanical fuse, unassembled. 
       FIG. 4  is a perspective view of the mechanical fuse, unassembled. 
       FIG. 5  is a perspective view of the mechanical fuse. 
       FIG. 6  a side view of the mechanical fuse, installed. 
       FIG. 7  is a cutaway side view of the mechanical fuse in a compressed position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates a lumbar support actuated by an actuation linkage that is a traction cable. In a seat  8 , an arching pressure surface  10  may be bowed or arched outwards to form a semi-rigid curve offering lumbar support to a seat passenger. The pressure surface  10  has an upper-end  12  and a lower-end  14 . The ends of the pressure surface are engaged with guide rods (obscured) along which they slide when the pressure surface  10  is arched. The guide rods in turn are attached to a frame of the seat  8  by mounts  16 . 
   Arching force is applied to the pressure surface by traction cable  20 . One end of the traction cable  20  is engaged with an actuator  22 . The engagement is designed such that movement of the actuator, as by a human handcrank or an electrical motor, will pull a traction cable wire  24  axially through and out from the traction cable sleeve  26 . 
   The other end of the traction cable  20  is engaged with the arching pressure surface  10 . Specifically, the sleeve  26  is attached to the top end  12  of the arching pressure surface. The traction cable wire  24  is attached to the bottom end  14  of the arching pressure surface. Accordingly, as the actuator  22  pulls the wire  24  out from the sleeve  26  at the actuator end, the lumbar support end of wire  24  will be pulled closer to the lumbar support end of the sleeve  26 , thus drawing the bottom end  14  to which the wire is attached and the top end  12  to which the sleeve is attached closer together. 
   As will be immediately appreciated by those with skill in the art, the arched, lumbar supporting position of the flexible panel  10  is maintained by a degree of tension held in place by the traction cable  20 . (Tension is held by any of a variety of locks, brakes or clutches usually incorporated in the actuators.) As will further be appreciated by those with skill in the art, an abusive load, comprised of force against the arching pressure surface  10  in a direction to flatten it, will impose a force on the traction cable pulling the traction cable wire  24  out from the traction cable sleeve  26  at the lumbar support end (and pulling the wire  24  into the sleeve  26  at the actuator  22  end). An abusive load will be received by the mechanical fuse as a compressive axial force. When a load is heavy enough, sudden enough or otherwise violent enough to exceed the expected design limit of the lumbar support, this abusive load risks damage to the lumbar support, particularly at its traction cable linkage. 
   The fuse  30  divides the sleeve into sections  26 A and  26 B. The wire  24  proceeds through the fuse  30  without interruption. 
   In a similar fashion, rigid links may also draw the top and bottom ends together. See, for example, U.S. Pat. No. 5,397,164, which is hereby incorporated by reference herein. Any of a wide variety of actuation linkages may have the mechanical fuse advantageously installed, provided the linkage allows for a selectable positioning of the ergonomic support, and receives abusive loads as a compressive force a long the axis of the linkage. 
     FIG. 2  is a cross-section of the mechanical fuse of the present invention. First cylindrical component  100  has a seat  102  for one section of a traction cable sleeve. First cylindrical component  100  also has an axial through hole  104  for allowing passage therethrough of the traction cable wire  24 . Annular to the through hole  104  is a spring seat  106  for internal spring  150 . 
   At the other end of first cylindrical component  100  has a collar  110  or a series of bosses or tabs. The collar has angled faces  112 . The collar is in sections, as described below. 
   The second cylindrical component  120  also has a seat  122  for a different traction cable sleeve section, or a different rod or other actuation linkage component. The second cylindrical component  120  also has an axial through hole  124  for allowing passage therethrough of the traction cable wire  24 . Concentric to this through hole  124  is an annular seat  126  for internal spring  150 . 
   The second cylindrical component  120  also has a groove  130 , or, alternatively, a series of holes, detents or slots. Groove  130  is positioned and dimensioned to engage collar  110  on the first cylindrical component  100 . Annular groove  130  has angled faces  132 . The angled faces  132  of annular groove  130  are dimensioned to correspond and closely cooperate with the oppositely angled faces  112  of the first cylindrical component  110  of the collar. When assembled, the faces  132  and  112  form a friction fit. 
   Internal to both cylindrical components  100  and  120  is the expansion spring  150 . Expansion spring  150  is seated at either end on each of the annular spring seats  106  and  126 . 
   Outside of the first cylindrical component  100  is a compression spring  140 . A metal C-spring may be used, or, alternatively, an O-ring, which may be softer than the C-spring. 
     FIGS. 3 and 4  are perspective views of the cylindrical components  100  and  120  of the mechanical fuse unassembled.  FIG. 5  is a perspective view of the assembled mechanical fuse. As is best seen in  FIG. 3 , one alternative embodiment of the flexing “collar”  110  is comprised of a series of axially oriented fingers that flex in a radial direction  200 . Collar  110  is actually in four sections, each of the sections being a free end of a finger  200 . In other words, each finger  200  has an inwardly oriented boss or tab. Fingers  200  alternate with non-flexing fingers  202 , which have no inwardly oriented collar projection. All of the fingers  200  and  202  are separated by slots  204 . Fingers  202  do not have an inwardly projecting collar component  110 . Rather, fingers  202  have an outwardly projecting flange  206  which along with flange  208  retain C-spring  140  when assembled. 
   Visible in  FIG. 4  on the second cylindrical or male component  120  are the circumferential holes or groove  130  sections that interact with the sectioned collar components  110  of Fingers  200 . Holes  130  are defined by faces including face  132  molded in component  120 . Angled face  132  in hole  130 , as was illustrated in  FIG. 2 , is dimensioned to closely cooperate with the angled faces  112  of collar sections  110 . Fingers  200  are naturally biased by their integral forming, as by plastic molding, to a position parallel with the axis of the cylinders  100  and  120  and the traction wire  24 . Accordingly, when so assembled collar sections  110  snap into holes  130 , establishing a friction fit between the faces  112  of collar sections  110  and the faces  132  of holes  130 . 
   Also visible on  FIG. 4  is an anti-rotation ridge  260  dimensioned to closely cooperate with an anti-rotation groove  160  inside cylindrical component  100 . The groove  160  is best seen in  FIG. 2 . 
     FIG. 5  is a perspective view of the assembled components showing the snap fit insertion of collar sections  110  in holes  130  and the retention of C-spring  140  by flanges  206  and  208 . 
   As will be apparent to those with skill in the art, any of a variety of alternative embodiments can achieve the functional interaction of components  100  and  120  that is required. Tabs and slots, bosses and detents, even a 360 degree collar interacting with a 360 degree groove (that is not a through-hole) will serve to achieve the releasable friction fit of the fuse and are considered to be within the scope of the present invention. 
   In assembly, a traction cable wire is inserted all the way through the mechanical fuse, through axial through holes  104  and  124  and through spring  150 . Traction cable sleeve segment such as segment,  26 A or  26 B is seated at either seat  102  or  122 . The other traction cable sleeve segment  26 B or  26 A is seated in the other sleeve seat. Alternatively, a bullet or cylindrical collar on the traction cable wire  24  may be seated opposite a sleeve segment. The spring,  150  is installed over the wire  24  until it is mounted against one or the other of the annular seats  106  or  126 . The cylindrical components  100  and  120  are slid in a male-female fashion into one another. One or both of the cylindrical components are flexible enough so that the first cylindrical component collar  110  may be slidingly installed over the side walls of second cylindrical component  120 . When the collar  110  reaches the groove  130 , it snaps into place. The collar and groove may be 360°, less than 360° or divided into circumferential sections. The dimensions, especially the length, of the cylindrical components and their collar  110  and groove  130  are dimensioned to correspond to a pre-configured range of motion for the traction cable. 
   In the depicted embodiment, a compression spring  140  in the form of a collar is snapped into place over the first cylindrical component  100  in order to supplement the natural bias of the first cylindrical component to hold the collar  10  seated in the groove  130 . Alternatively, the compression spring  140  may be omitted if the natural bias of the first cylindrical portion to remain seated is sufficient for the anticipated loads. 
   After the mechanical fuse has been installed in series with a traction cable, rods or other actuation linkage and assembled, the traction cable itself may be linked to an actuator and an ergonomic support. 
   Although the depicted embodiment is cylindrical, the scope of the present invention includes sliding components like  100  and  120  with varying cross sections, including without limitation, square, flat, oval and the like. 
   In operation, the mechanical fuse remains static in all respects during the normal use of the traction cable to which the fuse is attached. That is, when the forces exerted on the traction cable are within their normal pre-configured range for operation and use of the ergonomic support it actuates, the components of the mechanical fuse do not move relative to one another. The fuse components stay in a first relative position as long as the compressive axial forces remain below the preconfigured threshold. When an abusive load increases beyond the threshold, the friction fit between the bosses/collar and detents/groove releases and the fuse moves to a compressed position as shown in  FIG. 7 . 
   When an abusive load is encountered, it will force the end of the wire  24  at the ergonomic support and away from the end of the sleeve  26 . This force is applied to the mechanical fuse by a compressive axial force into the assembly through sleeve seat  102  and resisted by the opposing sleeve seat  122 . (Obviously, these positions are interchangeable, as the fuse may be equivalently installed in either direction.) In other words, an abusive force in the ergonomic support will be seen by the mechanical fuse as a compressive axial force tending to force first cylindrical component  100  and second cylindrical component  120  towards each other in an axial direction. When this abusive force is applied, it overcomes the force of static friction holding the angled faces  112  of collar  110  against the angled faces  132  of annular groove  130 . The natural bias of first cylindrical component&#39;s side walls to retain the collar and the groove together, with the force of the compression spring  140 , are overcome. The first cylindrical component  100  and second cylindrical component  120  slide towards each other or compress, with a male portion of one, which in the depicting embodiment is component  120 , sliding axially into a space designed to receive it in the female component, which in the depicted embodiment is first cylindrical component  100 . 
   By thus moving axially along the axis of the traction cable, the mechanical fuse assembly relieves the load being abusively applied. The relative length of the walls of the first cylindrical component  100  and second cylindrical component  120  may be pre-configured to substantially correspond to the anticipated range of motion of the traction cable for the particular ergonomic support attached to it. They may also be just long enough to relieve an anticipated abusive load. 
   Clearly, a load is defined as abusive by the degree of force required to move sectioned collar  110  out of annular groove  130 . Accordingly, the design of the strength, material, coefficient of friction, and angles of faces  112  and  132  and the strength of compression spring  140  will define the degree of force necessary to move the collar  110  out of the groove  130 , thereby also defining the threshold of what constitutes an abusive load. 
   Adjustment of the overload threshold may be achieved without refabricating the primary components of the fuse, in the depicted embodiments cylindrical components  100  and  120 , by adjusting the strength of the C-clamp  140 . By using a weaker C-clamp  140  the threshold for overloading and activating the fuse is lowered, and by using a stronger C-clamp the threshold is raised. 
   In the depicted embodiment the following parameters may be used. The angle of the both faces of collar  112  and groove  132 , to the axis of the fuse is between 70 and 80 degrees. The coefficient of friction 0.15 to 0.25 (unlubricated nylon against nylon). The typical triggering force is variable, but for lumbar supports and the components that need protection, it typically will be between 450 and 650 Newtons. The travel until the peak load is reached is in the 1–2 mm range. The total travel must be adjustable and is typically 20 to 60 mm. The reset force, which is determined by the spring constant and spring precompression has to be higher than the cable preload (lumbar in seat with foam and trim, but no occupant), which is typically between 20 and 100 Newtons. The radial forces per finger  200  (with a 4 fingers fuse) is typically in the range of 5 to 15 Newtons. 
   In order to reset the mechanical fuse, and through it the ergonomic support with which it is assembled, expansion spring  150  exerts a separating force on the first and second cylindrical components  100  and  120 . The outer walls  128  of second cylindrical component  120  are angled to accommodate the return path of the expanded collar  110  for resetting into annular groove  130 . 
   Because the abusive load is applied to the mechanical fuse as a compressor force, the mechanical fuse can be deployed for use with rigid linkage components such as rods, spokes or hard drawn wires. In the assembly of such a deployment, the step of inserting a wire  24  through both components  100  and  120  is omitted. Thereafter the step of seating cable sleeves into seats  102  and  122  is replaced by seating rods, spokes or other rigid components in seats  102  and  122 . The ends of the rods may be held in place simply by compression, or, in an alternative embodiment, a snap fit, screw, collar or other known fixation device may be used to retain an end of a rod in seats  102  and  122 . An alternative embodiment dedicated to use with rigid components may omit through holes  104  and  124 . Clearly, however, the depicted embodiment may be used with rigid devices as is. 
     FIG. 6  is a side view of the mechanical fuse installed in series with a traction cable, showing cable sleeve sections  26 A and  26 B, wire  24 , components  100  and  120 , external spring  114  and internal spring  150 . 
   In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. 
   The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
   As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.