Abstract:
A tethering system for a vehicle seat movable in at least a vertical direction. The system includes a sensor mechanism to detect the occurrence of a prescribed vehicle event. Upon detecting such an event, the tethering system acts to limit the vertical movement of the vehicle seat and/or draw the vehicle seat toward the surface on which the seat is mounted. The prescribed vehicle event can include a vehicle rollover, a vehicle collision, or an excessive vehicle acceleration.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to occupant restraint devices for vehicles. In one aspect, it relates to an apparatus for tethering a vehicle seat, which is mounted on a suspension pedestal, against unwanted movement relative to the vehicle floor. 
     BACKGROUND OF THE INVENTION 
     It is well known to mount a vehicle seat on a pedestal rather than securing it directly to the floor of the vehicle. Seat mounting pedestals may include mechanisms for adjustment of the static fore-aft position of the seat, and may also include mechanisms for adjustment of the static seat height. More sophisticated seat mounting pedestals are also known which include vertical and/or fore-aft suspension devices, for example springs, pneumatic cylinders, or air bags, which allow controlled movement (also known as “travel”) of the seat with respect to the vehicle floor during operation of the vehicle. This seat travel tends to isolate the seat (and thus the occupant) from vibration and bouncing. 
     Most vehicles are now required to provide an occupant restraint system to reduce the likelihood of occupant injury during high acceleration events such as vehicle collisions or rollovers. According to Federal Motor Vehicle Safety Standard (FMVSS) testing, occupant injury is reduced when the forward and upward movement of the occupant is limited as much as possible. The limitation of the occupant&#39;s overall movement is best accomplished by restraining the occupant against movement relative to the seat while simultaneously restraining the seat itself against forward and/or upward movement relative to the vehicle floor. Thus, the seat mounting system of a vehicle is often a component of the occupant restraint system. 
     In some applications, for example in the field of commercial vehicles and long-haul trucks, a wide variety of seats and suspension pedestals are produced by numerous manufacturers. Seats and pedestals are typically manufactured separately, rather than as a unit, so that a vehicle&#39;s owner can select individual component according to his or her preferences. The selected components are then installed in the vehicle by the builder. The builder must ensure that the selected components are compatible in terms of both seat suspension operation and occupant restraint operation. 
     To accommodate the wide variety of seat/pedestal configurations, it has become conventional practice for the occupant restraint system used in trucks having pedestal mounted seats to comprise two principle components, namely, a seat belt apparatus and a seat tethering apparatus. The first component of the restraint system, the seat belt apparatus, ensures that the occupant remains positioned in the seat during a high acceleration event. The seat belt apparatus typically comprises conventional seat belt webbing and a latch mechanism, and may further comprise a shoulder belt and/or belt tensioning mechanisms, all of which are conventional and known in the art for restraining an occupant in a seat. Note, however, that the seat belt webbing and latch are not anchored to the floor of the vehicle, but rather are attached to a structural member, known in the industry as the interconnect point (hereafter “ICP”), which is located on the lower rear portion of the seat or on the upper rear portion of the pedestal. 
     The second component of the occupant restraint system, the seat tethering apparatus, must restrain the seat against forward or upward movement relative to the floor of the vehicle during high acceleration events, a requirement which cannot generally be satisfied by the seat mounting pedestal alone. One commonly known seat tethering apparatus includes a pair of tether straps, each of which has one end connected to the ICP and another end connected to an anchor point located on the vehicle floor behind the seat. The tether straps are made of webbing material such as that used for seat belts. The tether straps may include mechanisms (one on each strap) to allow manual adjustment in length to accommodate vehicle-to-vehicle differences in the ICP-to-anchor distance and to accommodate adjustments in the static position of the seat relative to the vehicle floor. Proper use of the seat tethering apparatus requires the operator to manually adjust the length of each tether strap so that they are taut between the floor of the vehicle and the ICP on the base of the seat. In this manner, the forward and upward movement of the vehicle seat, and thus of an occupant properly belted into the seat, can be substantially limited relative to the floor of the vehicle during a collision. As a result, the occupant is less likely to incur substantial injuries by using the restraint system. 
     The conventional practice of using manually adjustable tether straps, however, does not necessarily ensure that the occupant will be optimally retrained in the event of a collision. Optimal restraint requires the length of each seat tether to be adjusted such that substantially all slack in the straps is eliminated. Ideally, the length of each tether strap would be adjusted to eliminate all slack each time the seat position is changed. Given human nature, however, many operators often fail to adjust the tether straps to eliminate the slack after each change in seat position, and further, some operators purposely adjust the tether straps with extra slack so that a full range of seat adjustment is possible at all times. Further, when the pedestal incorporates a suspension system, some slack must be intentionally left in the tether straps to accommodate the desirable movement of the seat through its range of suspension “travel” due to the weight of the occupant and due to dynamic forces (e.g., bouncing) during normal operation of the vehicle. As a result of these factors, there typically will be some slack in conventional seat tethers during normal vehicle operation. This slack represents additional movement through which the occupant will travel during a collision before being restrained by the restraint system, and consequently an increased chance of injury. Therefore, a need exists for a seat tethering apparatus that automatically minimizes the slack in the seat tethers during normal vehicle operation, but without hindering the seat suspension functions and without being dependent on an operator&#39;s diligence to tighten the tether straps. 
     Another concern regarding pedestal mounted vehicle seats relates to accidents in which a vehicle undergoes a rollover event. In such cases, the roof of the vehicle may be crushed inwards, thereby reducing the distance between the floor and the roof. Even though a conventional seat tethering apparatus can prevent the seat and occupant from moving toward the roof, it does nothing to protect the occupant from striking/being struck by the vehicle roof as it moves toward the floor. Therefore, a need exists for a seat tethering apparatus that increases the distance between the occupant&#39;s head and the roof of the vehicle during a rollover event to reduce the chance of injury. 
     SUMMARY OF THE INVENTION 
     Many of the needs outlined above are addressed by the present invention hereof. It is an object of the present invention to provide a seat tethering apparatus that automatically minimizes the slack in the seat tethers during normal vehicle operation, but without hindering the seat suspension functions and without being dependent on an operator&#39;s diligence to tighten the tether straps. 
     It is another object of the present invention to provide a seat tethering apparatus that increases the distance between the occupant&#39;s head and the roof of the vehicle during a rollover event to reduce the chance of injury. 
     An apparatus for tethering a vehicle seat is provided that can be used for many vehicle applications, but which is particularly suited for use in the cabs of trucks, vans, and other large vehicles. The apparatus includes a webbing member, a sensing mechanism, and a retractor, wherein the retractor includes a spool assembly, a locking mechanism, and a biasing mechanism. The webbing member has one end attachable to a vehicle floor and a second end wound around the spool assembly of the retractor, wherein the retractor is attachable to a vehicle seat. The sensing mechanism senses at least two characteristics: a retractor operation characteristic and a vehicle collision characteristic. The sensing mechanism further produces a signal indicating which characteristic is currently being sensed. The locking mechanism of the retractor operates in response to the signal produced by the sensing mechanism. Specifically, the locking mechanism remains unlocked in response to the retractor operation characteristic and locks in response to the vehicle collision characteristic. The biasing mechanism of the retractor applies a constant force that urges the spool assembly in a direction that winds more of the webbing member toward the retractor. Accordingly, when the retractor operation characteristic is sensed, then the webbing member can be withdrawn from or retracted into the retractor depending on whether the tension applied to the webbing member is more or less than that applied by the biasing mechanism. Alternatively, when the vehicle collision characteristic is sensed, then the webbing member can be retracted further into the retractor if the tension applied is less than that applied by the biasing mechanism. The locking mechanism prevents the webbing member from being withdrawn further from the retractor. 
     In another embodiment, the webbing member includes an intermediate portion that passes through a corresponding guide portion, or webbing loop, attachable to a vehicle seat. In yet another embodiment, a retractor driving mechanism is included which applies a specified force to the webbing member in response to the vehicle collision signal produced by the sensing mechanism, thereby further retracting the webbing member into the retractor during a collision. In additional embodiments, various known types of drive sources can be used for the retractor driving mechanism, including a gas generator and a piston, a pneumatic piston, an air motor, an electric motor, and the like. In still further additional embodiments, various known types of sensors can be used for the sensing mechanism, including a centrifugal sensor, a pendulum sensor, an inertia sensor, a multi-axis sensor, an impact sensor, an electronic sensor, an accelerometer sensor, and the like. 
     In another embodiment, the apparatus for tethering a vehicle seat can include two or more webbing members, each of which is wound around the spool assembly of the retractor. In this embodiment, each of the webbing members includes an intermediate portion that passes through a corresponding guide portion, or webbing loop, attachable to a vehicle seat. 
     In another embodiment, the retractor can be attachable to an interior portion of a vehicle, and the webbing member can have a first end attachable to a vehicle seat and a second end wound around the spool assembly of the retractor. 
     In another embodiment, an apparatus is provided for effecting the method of retracting a vehicle seat when a vehicle is rolling over, including a vehicle seat, a sensor, and a retractor mechanism. In this embodiment, the sensor can at least sense whether a vehicle rollover is occurring and produce a signal when such a rollover begins. The retractor mechanism operates in response to this vehicle rollover signal and actively retracts the vehicle seat toward a floor of the vehicle. A further embodiment includes a vehicle seat, a retractor, a webbing member, a sensor mechanism, and a retractor driving mechanism. The retractor is attached to the base of the vehicle seat and includes a spool assembly. This embodiment also includes a webbing member with a first end attachable to the vehicle and a second end wound around the spool assembly of the retractor. The retractor driving mechanism causes the spool assembly to rotate in a direction that draws more of the webbing member into the retractor when a vehicle rollover signal is received from the sensor mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better and more complete understanding of the present invention and the advantages thereof will be gained from the following detailed description, claims, and accompanying drawings in which: 
     FIG. 1 is a front view of a conventional pedestal mounted vehicle seat having a tethering apparatus; 
     FIG. 2 is a front view of a pedestal mounted vehicle seat having a tethering apparatus according to a first embodiment of the present invention; 
     FIG. 3 is a back view of a pedestal mounted vehicle seat having a tethering apparatus according to a second embodiment of the present invention; 
     FIG. 4 is a side view of the seat and tethering apparatus of FIG. 3; 
     FIG. 5 is a back view of a pedestal mounted vehicle seat having a tethering apparatus according to a third embodiment of the present invention; 
     FIG. 6 is a back view of a pedestal mounted vehicle seat having a tethering apparatus according to a fourth embodiment of the present invention; 
     FIG. 7 is a back view of a pedestal mounted vehicle seat having a tethering apparatus with an active retractor according to a fifth embodiment of the present invention; 
     FIG. 8 is a back view of a pedestal mounted vehicle seat having a tethering apparatus with an active retractor according a sixth embodiment of the present invention; and 
     FIG. 9 is an enlarged front view of the retractor mechanism of FIGS. 3-5 and  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the accompanying figures, wherein like reference numerals designate like or corresponding parts throughout the several views, the present invention is explained hereafter. 
     Referring first to FIG. 1, shown is a pedestal mounted vehicle seat  20  having a tethering apparatus according to the conventional art. The vehicle seat  20  includes a seat frame  22  having attached thereto a seat cushion  24  and a seat back  26  for supporting an occupant (not shown). The vehicle seat  20  can be of conventional construction as is known in the art. The seat  20  is mounted to a vehicle floor  28  by a pedestal  30  connected between the floor  28  and seat frame  22 . The mounting pedestal  30  can be of conventional construction as is known in the art, and can include known mechanisms (not shown) for static adjustment of seat height and fore/aft position. Further, the seat  20  can include known mechanisms allowing up/down suspension travel (indicated by arrow  32 ) and/or fore/aft suspension travel during normal operation. For purposes of this detailed description, all seat positions and movements are described relative to the vehicle floor  28 , unless expressly stated otherwise. An ICP (interconnect point) bracket  34  is rigidly attached to the upper portion of the pedestal  30 , and an ICP  36  is rigidly attached at each end of the ICP bracket  34 , providing a connection point for the occupant restraint system components as described below. 
     The vehicle seat  20  according to the prior art further includes an occupant restraint system including a seat belt apparatus  38  and a seat tether apparatus  40 . The seat belt apparatus  38  includes seat belt webbing  42  and a buckle mechanism with latch  44  and latch plate  46 . The seat belt webbing  42  extends from the latch plate  46  and is connected to one of the ICPs  36  (at the point indicated by arrow  47 ). The latch  44  is connected to the other ICP  36  by a connecting member  48 . The seat belt apparatus  38  shown in FIG. 1 also includes a shoulder belt portion  50  which extends from the latch plate  46 , through a turning loop  52  mounted on the vehicle wall  53  to a tensioning/locking mechanism  54  mounted on the vehicle floor  28 . It will be readily apparent that when an occupant of the seat  20  properly positions the seat belt apparatus  38  around his or her body and buckles the latch plate  46  into the latch  44 , the seat belt webbing  42 , latch  44 ,  46  and connecting member  48  will transmit any forward or upward forces on the occupant&#39;s body to the ICPs  36 . Because the seat belt apparatus  38  is of conventional construction and function, it will not be further described. 
     The second component of the occupant restraint system, the seat tethering apparatus  40 , must restrain the seat  20  against forward or upward movement relative to the floor  28  of the vehicle during high acceleration events, a requirement which cannot generally be satisfied by the seat mounting pedestal  30  alone. The commonly known seat tethering apparatus  40  shown in FIG. 1 includes a pair of tether straps  56 , each of which has one end connected to the ICP  36  and another end connected to an anchor point  58  located on the vehicle floor  28  behind the seat. The tether straps  56  are made of webbing material such as that used for seat belts. The tether straps  56  may include mechanisms  60  (one on each strap) to allow manual adjustment in length to accommodate vehicle-to-vehicle differences in the ICP-to-anchor distance and to accommodate adjustments in the static position of the seat  20  relative to the vehicle floor  28 . Proper use of the tethering apparatus  40  requires the operator to manually adjust the length of each tether strap  56  so that they are taut between the floor  28  of the vehicle and the ICP  36  of the seat  20 . In this manner, the forward and upward movement of the vehicle seat  20 , and thus of an occupant properly belted into the seat, can be substantially limited relative to the floor  28  of the vehicle during a collision. 
     A first embodiment according to the present invention is shown in FIG.  2 . The ICP bracket  34  provides an ICP  36  on the left and right sides of the seat  20 . A seat belt apparatus  38  is secured to the seat  20  at the right ICP  36  so as to limit the movement of an occupant secured to the seat  20  with the seat belt apparatus  38  relative to the seat  20 . Two adjustable suspension mechanisms  62  are attached to the seat frame  22 . The adjustable suspension mechanisms  62  allow movement of the seat  20  relative to the floor  28  in a vertical direction and a fore/aft direction such that the position of the seat  20  can be adjusted as desired. 
     The seat tethering apparatus  40  includes a retractor  66 , a sensing mechanism  68 , and a webbing member  70  that has a first end  72  attached to the floor  28  and a second end  74  attached to the retractor  66 . In the first embodiment shown in FIG. 2, an anchor  76  is rigidly attached to the floor  28 , and the first end  72  of the webbing member  70  is securely attached to the floor  28 . However, the first end  72  of the webbing member  70  can be secured to the floor  28  in any manner that securely retains the first end  72 . The free length  78  a variable distance measured between the floor  28  and the frame  22 , varies in accordance with the operation of the seat tethering apparatus  40 . 
     In the first embodiment, the retractor  66  is attachable to the frame  22  of the seat  20 . A support bracket  80  is rigidly attached to the frame  22  of the seat  20 , and the retractor  66  is rigidly attached to the support bracket  80 . However, other alternatives can be used for attaching the retractor  66  to the seat frame  22 , such as bolts, clamps, enclosures incorporated into the seat frame  22  that enclose and retain the retractor  66 , or any other method or device for maintaining the position of the retractor  66  relative to the frame  22  of the seat  20 . 
     In the first embodiment of the present invention, the retractor  66  is of a type generally known and used in the art of retractable vehicle seat belts. The use of known retractors of this type will substantially decrease the cost of the seat tethering apparatus  40  because of the wide commercial availability. Furthermore, many variations of these retractors are currently on the market such that retractors of different shapes and sizes can be used and the seat tethering apparatus  40  of the present invention can thus be adapted to many different applications. 
     A retractor  66  of the type generally used for vehicle seat belts includes a spool assembly  82 , a locking mechanism  84 , and a biasing mechanism  86 . The second end  74  of the webbing member  70  is wrapped around the spool assembly  82 . Referring to FIG. 9, it can be seen that the spool assembly  82  is mounted in the retractor  66  such that it may rotate in two different directions, a webbing retraction direction  88  and a webbing withdrawal direction  90 . Rotating the spool assembly  82  in the webbing retraction direction  88  wraps an additional length of webbing member  70  around the spool assembly  82  and thereby decreases the free length  78 . Conversely, rotating the spool assembly  82  in the webbing withdrawal direction  90  unwraps a certain length of the webbing member  70  from around the spool assembly  82  and thereby increases the free length  78 . 
     Referring to FIG. 9, the locking mechanism  84  of the retractor  66  prevents the rotation of the spool assembly  82  when it is in a locked position. The importance of the locking mechanism  84  is that it prevents rotation in the webbing withdrawal direction  90  when in the locked position, thus preventing the free length  78  from increasing and thereby preventing the movement of the seat  20  relative to the floor  28  during a period of acceleration and/or impact. Whether or not the locking mechanism  84  locks the rotation of the spool assembly  82  in the webbing retraction direction  88  in addition to the webbing withdrawal direction  90  does not significantly affect the operation of the seat tethering apparatus  40 . Even if the locking mechanism  84  does lock in the webbing retraction direction  88 , it is extremely unlikely that any force in the webbing retraction direction would overcome the force applied in the webbing withdrawal direction  90  during a collision or other high acceleration and/or impact situation that causes the locking mechanism to lock. 
     The biasing mechanism  86  of the retractor  66  applies a constant predetermined force to the spool assembly  82  that urges the spool assembly to rotate in the webbing retraction direction  88 . When the locking mechanism  84  is not in the locked position, the force applied by the biasing mechanism  86  constantly urges the free length  78  to decrease. The rotation of the spool assembly  82  is dependent on whether the counteracting force applied to the webbing member  70  is greater than, equal to, or less than predetermined force applied by the biasing mechanism  86 . In other words, the rotation of the spool assembly  82  depends on whether the seat  20  is being adjusted or not. 
     If the seat frame  22  is adjusted to a position closer to the floor  28 , then the force applied by the biasing mechanism  86  will be greater than a counteracting force applied to the webbing member  70  by movement of the seat frame  22 , thus causing rotation of the spool assembly  82  in the webbing retraction direction  88  and decreasing the free length  78 . Conversely, if the seat frame  22  is adjusted to a position further away from the floor  28 , then the force applied by the biasing mechanism  86  will be less than a counteracting force applied to the webbing member  70  by movement of the seat frame  22 , thus causing rotation of the spool assembly  82  in the webbing withdrawal direction  70  and an increase in the free length  78 . Of course, if the locking mechanism  84  is in the locked position, then the counteracting force applied to the webbing member  70  by the attempted movement of the seat frame  22  will be inhibited by the locking mechanism  84 , thus preventing any increase in the free length  78  and restricting any relative motion between the seat frame  22  and the floor  28 . Essentially, the constant force applied by the biasing mechanism  86  in the webbing retraction direction  88  takes up any slack in the webbing member  70  such that the free length  78  is always taut between the floor  28  and the retractor  66  (and thereby taut between the floor  28  and the seat frame  22 ). In this manner, the free length  78  is automatically adjusted by the biasing mechanism  86  without any need for manual adjustment by an individual. 
     The mounted position of the sensing mechanism  68  is not particularly critical to the present invention; provided however, the sensing mechanism  68  should be mounted so as to experience the accelerations experienced by the floor  28  while also maintaining a communication link  92  with the locking mechanism  84  of the retractor  66 . As illustrated in FIG. 2, one location for the sensing mechanism  68  is to attach it directly to the floor  28 , but it can also be mounted to the seat frame  22  with the retractor  66 , to a dashboard inside the vehicle, or in many other locations in and around the vehicle. At any given time, the sensing mechanism  68  can sense whether the floor  28  is experiencing a specified range of normal accelerations (retractor operation characteristic) or an acceleration in excess of that specified range (vehicle collision characteristic). The sensing mechanism  68  produces a signal indicative of that characteristic and communicates that signal to the locking mechanism  84  of the retractor  66 . The locking mechanism  84  then responds to the signal communicated from the sensing mechanism  68  by (i) locking the spool assembly  82  if a vehicle collision characteristic signal is received or (ii) maintaining an unlocked spool assembly  82  if a retractor operation characteristic signal is received. 
     The sensing mechanism  68  can be any type of sensor commonly known in the art that can sense acceleration. For example, the following types of sensors are particularly well suited to be used as the sensing mechanism  68 : centrifugal sensors, pendulum sensors, inertia sensors, multi-axis sensors, impact sensors, electronic sensors, accelerometer sensors, and the like. The scope of the present invention is not limited to the type of sensor used for the sensing mechanism  68 , but rather encompasses any commonly known sensor that can sense acceleration and can facilitate issuance of a signal on the communication link  92  to the locking mechanism  84  of the retractor  66 . 
     The-advantage of the seat tethering apparatus  40  is a system that provides added support to the vehicle seat  20  to limit motion of the seat  20  relative to the vehicle floor  28  during periods of excessive acceleration such that may occur in impact/collision scenarios. In particular, the free length  78  in the present invention is automatically adjusted to remove any slack that occurs as a result of adjusting the vehicle the seat  20 , whether the seat is adjusted manually by an individual or adjusted automatically by the weight of the individual seated on it. By automatically removing the slack in the webbing member  70 , the present invention restricts the amount of secondary accelerations and impact effects passed to an individual belted to the seat  20  when the vehicle experiences periods of extreme acceleration, as during collisions and rollovers. Based on the relationship between the number of accelerations to which the individual is subjected and the extent of injuries experienced, the present invention may help to reduce the risk of serious or fatal injuries as compared to those experienced when the prior seat tethers are used. 
     Another embodiment of the present invention incorporates a retractor driving mechanism  90  in communication with the sensing mechanism  68  and the retractor  66 . As does the locking mechanism  84 , the retractor driving mechanism  90  activates in response to a vehicle collision characteristic signal sent by the sensing mechanism  68 . When activated, the retractor driving mechanism  90  actively drives the retractor  66  by rotating the spool assembly  82  in the webbing retraction direction  88 . As a result, if a retractor driving mechanism  90  is incorporated into the present invention, then the locking mechanism  84  should only lock the spool assembly  82  from rotating in the webbing withdrawal direction  90  such that the retractor driving mechanism  90  can still drive the spool assembly  82  to rotate in the webbing retraction direction  88 . The retractor driving mechanism  90  can be any mechanism that can actively force rotation of the spool assembly  82  of the retractor  66 . Some examples of acceptable retractor driving mechanisms  90  include a gas generator and piston, a pneumatic piston, an air motor, an electric motor, and the like. However, many other possible retractor driving mechanisms  90  will be apparent to those skilled in the art. 
     Other variations on the present invention can also be used to improve the performance of the seat tethering apparatus  40 . For example, one variation of the apparatus is to use more than one the seat tethering apparatus  40  for a single vehicle seat  20 . In other words, additional support during a period of excessive acceleration may be provided by using two or more retractors  66 , two or more sensing mechanisms  68 , and two or more webbing members  70 . If the two or more retractors  66  are attached to the seat  20  at different points, then support may be provided in multiple directions at the same time during a collision or other high acceleration event. Accordingly, the amount of movement of the seat  20  relative to the floor  28  can be restricted even more if multiple seat tethering apparatus according to the present invention are used on a single seat  20 . 
     Although additional support can be provided to the seat  20  by using multiple seat tethering apparatus  40 , it may be more efficient and economical to use multiple webbing members  70  with a single retractor  66  and a single sensing mechanism  68 , as shown in FIGS. 3 and 4. It can be seen in FIG. 3 that the seat  20  is identical to that described in FIG. 2, but the adjustable suspension mechanism  62  varies. However, this difference in the suspension mechanism  62  does not change the use of the seat tethering apparatus  40 . As with the embodiment shown in FIG. 2, the embodiment shown in FIGS. 3 and 4 utilizes a single retractor  66  and a single sensing mechanism  68  with a communication link  92 . However, the preferred embodiment utilizes two webbing members  70  instead of a single webbing member  70 , each webbing member has a first end  72 , a second end  74 , and an intermediate portion  94 . Furthermore, two guide portions  96  are rigidly attached to the ICPs  36 , respectively. Each webbing member  70  is threaded through a corresponding guide portion  96  such that the intermediate portion  94  of each the webbing member  70  is supported by a corresponding guide portion  96 . As can be seen in FIG. 4, the guide portions  96  have an aperture  96   a  through which the webbing members  70  can pass, wherein the webbing members  70  can slide in both directions so that any slack in the webbing members  70  is removed by operation of the retractor  66 . In this preferred embodiment, the retractor  66  operates identically as described for the first embodiment illustrated in FIG.  2 . The guide portions  96  can take the form of any apparatus that will redirect the webbing members  70  while still allowing the webbing members  70  to freely slide. 
     As shown in FIG. 3, the first end  72  of each webbing member  70  is attached to the floor  28 . Preferably, the first ends  72  are attached at locations on the floor  28  separate from each other such that additional support is provided by restricting the relative motion of the seat  20  from multiple points of support. As with the embodiment illustrated in FIG. 2, the first ends  72  of the webbing members  70  can be attached to the floor  28  by any means that maintains a secure connection, e.g., two anchors  76 . The second ends  74  of the webbing members  70  are both wrapped around the spool assembly  82  of the retractor  66  in the same direction such that rotation of the spool assembly  82  in the webbing retraction direction  88  retracts both the webbing members  70 , and the rotation of the spool assembly  82  in the webbing withdrawal direction  90  increases the available operative length of the webbing members  70 . The guide portions  96  are necessary to redirect the webbing members  70  such that they may be attached to the floor  28  at separate locations and both may still be properly wrapped around the spool assembly  82  of the retractor  66 . Taken together, FIGS. 3 and 4 best illustrate that the webbing members  70  are redirected by the guide portions  96  such that a downward force(s) can be applied to the seat  20  at separate points during periods of excessive acceleration. This application of force at separate points of the seat  20  better restricts the movement of the seat  20  relative to the floor  28 . It can be further appreciated that the present invention is not limited to a seat tethering apparatus  40  with only two webbing members  70  and guide portions  96  but can incorporate additional webbing members  70  and guide portions  96  to provide additional points of support to the vehicle seat  20 . Each additional point of support provides an additional direction in which relative movement between the vehicle the seat  20  and the floor  28  is restricted. 
     Still another embodiment of the present invention is illustrated in FIG.  5 . Rather than attaching the retractor  66  to the seat  20  as with the embodiments shown in FIGS. 2-4, this third embodiment attaches the retractor  66  directly to the floor  28 . Furthermore, unlike the embodiment shown in FIGS. 3 and 4 wherein the guide portions  96  are attached to the ICPs  36 , the guide portions  96  in this third embodiment are attached directly to the floor  28 . While the second ends  74  of the webbing members  70  are still wrapped around the spool assembly  82  of the retractor  66  and the intermediate portions  94  are threaded through the guide portions  96 , the first ends  72  of the webbing members  70  are secured directly to the ICPs  36 . As with the other embodiments, wherein the first ends  72  could be attached to the floor  28  in any manner appropriate, the first ends  72  of the webbing members  70  in this embodiment can also be attached to the ICP  36  in any appropriate manner. For example, the first ends  72  are shown to be secured to the loops  98  that are rigidly attached to the ICP  36 , respectively. 
     It can be further appreciated that a similar configuration, wherein the retractor  66  is rigidly attached to the floor  28  instead of the seat  20 , can also be applied in embodiments including only one the webbing member  70 , including the configuration having more than two webbing members  70  and more than two guide portions  96  as well as more than one retractor  66  with more than one webbing member  70 . 
     As is apparent from the depiction of the seat tethering apparatus  40  of the present invention being used with different adjustable suspension mechanisms  62  in FIGS. 2 and 3, the seat tethering apparatus  40  can be easily adapted to different seat and suspension mechanism configurations. If the configuration of the seat  20  and suspension mechanism  62  is such that there is not enough space directly underneath (or close to directly underneath) the seat  20 , additional guide portions can be utilized to redirect webbing members from the desired point of support on the seat  20  to the retractor  60 . This adaptability also provides the advantage that the seat tethering apparatus  40  of the present invention can be installed to existing vehicle seat and suspension mechanism configurations with little difficulty. As such, it should be appreciated that the scope of the present invention is not limited to only those vehicle seat and suspension mechanism configurations depicted in FIGS. 2-5. 
     Other embodiments of the seat tethering apparatus of the present invention is shown in FIGS. 6-8, wherein provision is made to actively retract seat  120  when a rollover of the vehicle begins to occur. When a vehicle rolls over onto its roof, many of the fatal injuries to passengers in the vehicle occur as a result of the collapse of the roof onto the heads and upper bodies of the passengers. As a result, if the space between the roof of the vehicle and the heads and upper bodies of the passengers can be maintained or even increased, then the probability of contact injuries should be reduced. Accordingly, when a rollover occurs, it is desirable to automatically retract seat  20  toward the floor  28  such that the head and upper body of the individual seated in seat  20  is as far away as possible from the roof of the vehicle (not shown). 
     The active retracting embodiment of the present invention includes a seat  20 , a sensor mechanism  68   a , a retractor mechanism  100 , and a retractor driving mechanism  102 , as illustrated in FIGS. 6 and 7. As with the embodiments already described, the sensor mechanism  68   a  can be mounted in a variety of positions as long as it experiences the same relative motion experienced by the floor  28  and remains in communication with the retractor driving mechanism  102  through a communication link  92 . As shown in FIG. 6, one preferred location for the sensor mechanism  68   a  is to attach it directly to the floor  28 , but it can also be mounted to the seat  20  along with the retractor mechanism  100 , to a dashboard inside a vehicle, or in many other locations in and around the vehicle. At any given time, the sensor mechanism  68   a  can sense whether the floor  28  (i.e., the vehicle) is subject to normal vehicle operations (a normal operation characteristic) or is experiencing a rollover of the vehicle (a vehicle rollover characteristic). In response to the characteristic sensed by the sensor mechanism  68   a , the sensor mechanism  68   a  produces a signal indicative of that characteristic and communicates that signal to the retractor mechanism  100 . The retractor mechanism  100  then responds to the signal communicated from the sensor mechanism  68   a  by actively retracting the seat  20  if the vehicle rollover characteristic signal is received or remaining passive if the normal operation characteristic signal is received. 
     Similar to the sensing mechanism  68 , sensor mechanism  68   a  can be any type of sensor generally known in the art that can sense a rollover. Sensing a rollover can involve sensing whether acceleration to one side or the other has exceeded a specified threshold, or it can involve sensing whether the angle of the vehicle has exceeded a specified threshold. As with the sensing mechanism  68 , the following types of sensors are particularly well suited to be used as sensor mechanism  68   a : centrifugal sensors, pendulum sensors, inertia sensors, multi-axis sensors, impact sensors, electronic sensors, accelerometer sensors, and the like. The scope of the present invention is not limited by the type of sensor used for sensor mechanism  68   a , but rather encompasses any generally known sensor that can sense a rollover and can facilitate issuance of a signal on the communication link  92 . To function in cooperation with retractor mechanism  100 , the retractor driving mechanism  102  can be any type of device that can actively retract the seat  20  toward the floor  28 . Examples of acceptable retractor driving mechanisms  102  are a gas generator and piston, a pneumatic piston, an air motor, an electric motor, and the like. Other possibilities for driving the retractor mechanism  100  and the sensor mechanism  68   a  will become apparent to those skilled in the art. 
     In the embodiment illustrated in FIG. 7, it can be seen that the seat tethering apparatus  62  for actively retracting the seat  20  can include a retractor  66 , a webbing member  70 , a sensor mechanism  68 , and a retractor driving mechanism  102  in a configuration similar to that already described with respect to FIGS. 2-4. The webbing member  70  has a first end  72  securely attached to the floor  28 , wherein the first end  72  can be secured by use of an anchor  58  or any other means by which a connection between the floor  28  and the first end  72  is securely maintained. The webbing member  70  also has a second end  74  attached to the retractor  66 . A free length  78  extends between the floor  28  and the frame  22 . In particular, the retractor  66  includes a spool assembly  82 , around which the second end  74  of the webbing member  70  is wound. The spool assembly  82  is freely rotatable in both a webbing retraction direction  88  and a webbing withdrawal direction  90 , whereas driving the retractor  66  can cause the free length  78  may be desirably decreased or increased, respectively. The retractor driving mechanism  102  provides a driving force to rotate the spool assembly  82  in the webbing retraction direction  88  only when the sensor mechanism  68  communicates a vehicle rollover characteristic signal. At all other times, the spool assembly  82  is preferably freely rotatable in either direction. 
     As with the embodiments discussed above, variations of this preferred embodiment will become apparent to those skilled in the art. One particular preferred embodiment is depicted in FIG. 8 wherein multiple webbing members  70  are included, each webbing member  70  having respective first ends  72  attached to the floor  28  at different locations and having second ends  74  wrapped around the spool assembly  82  of the retractor  66 . Furthermore, each webbing member  70  includes an intermediate portion  94  passing through a corresponding guide portion  96  which is attached to ICPs  36  on the seat  20 . In this preferred embodiment, activation of the retractor driving mechanism  102  in response to a received vehicle rollover characteristic signal from the sensor mechanism  68   a  decreases the free length  78  by rotating the spool assembly  82  retraction direction  88 , thereby pulling seat  20  closer to the floor  28 . 
     Signals issued by the sensory mechanism  68  are in accord with that earlier described in the context of the embodiment illustrated in FIG.  3 . 
     It will be readily apparent that the seat tethering apparatus of the present invention can also be used in other settings, for example in vans, locomotives, and any other vehicles wherein it is desirable to limit the movement of a seat relative to a vehicle floor or frame. 
     It is to be understood that even though the above numerous characteristics and advantages of the invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principle of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.