Energy absorbing system for blast mitigation of support elements such as suspended seats or stretchers in military vehicles |
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申请号 | US13506808 | 申请日 | 2012-05-17 | 公开(公告)号 | US20130033056A1 | 公开(公告)日 | 2013-02-07 |
申请人 | George C. Tunis, III; Scott Kendall; | 发明人 | George C. Tunis, III; Scott Kendall; | ||||
摘要 | An energy absorbing system for blast mitigation is provided for a suspended support element, such as a gunner seat or medical stretcher, in a vehicle. An energy absorbing element is located in series within at least one suspension element of the seat or stretcher. The energy absorbing element includes an extensible section having a contracted, folded configuration and an extended configuration. A retention element, such as stitching or entangled interlocking fibers, retains the energy absorbing element in the contracted configuration. The retention element remains intact when the energy absorbing element supports a load from the person on the seat or stretcher and fails over a period of time when an explosive force is applied to the vehicle from underneath, causing the vehicle to move upwardly, the extensible section thereby extending in length and absorbing energy. Injury to the person can thereby be reduced. | ||||||
权利要求 | What is claimed is: |
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说明书全文 | This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/574,610, filed on Aug. 5, 2011, the disclosure of which is incorporated by reference herein. In some military vehicles, a weapons mount is provided in the center. The weapons mount includes an opening formed in the vehicle roof. A seat for a gunner is suspended below the opening, typically by straps made from tightly woven webbing. The gunner sits in the seat such that a portion of the upper body extends through the opening to operate a weapon mounted to the weapons mount. Such military vehicles may be subject to under-belly blasts from improvised explosive devices (IEDs), mines, and other explosive events. These under-belly blasts can accelerate the occupant of the gunner seat upwardly out of the vehicle. In other military vehicles, seats are suspended from the ceiling of the vehicle. In military vehicles for medical purposes, stretchers for injured personnel are suspended from the ceiling of the vehicle. An under-belly blast can propel an occupant of the seat or stretcher into the ceiling. An energy absorbing system for blast mitigation is provided for a support element, such as a suspended gunner seat or a medical stretcher, for a person in a vehicle. The system includes an energy absorbing element disposed in series with at least one suspension element of the seat or other support element. The energy absorbing element is a longitudinal element, such as a woven strap, capable of carrying a tensile load. The energy absorbing element comprises an extensible section having a contracted configuration. The extensible section is configured with an initiation force to initiate extension from the contracted configuration, such that when a load on the vehicle is below the initiation force, no extension occurs and the support element is retained in suspension below the upper end, and when a load is applied to the vehicle that is above the initiation force, the extensible section extends in a controlled manner that absorbs energy. The contracted configuration comprises one or more folds of the extensible section retained in a folded orientation with adjacent portions abutting. A retention element is disposed to retain the extensible section in the contracted configuration. The retention element is configured to remain intact when the energy absorbing element, in series with the suspension element, supports a load from the person on the support element and to fail over a period of time, for example, to pull apart or rip apart, when an explosive force is applied to the vehicle from underneath, causing the vehicle to move upwardly. As the retention element fails, the extensible section extends in length and absorbs energy of the blast, so that the energy does not return back into the system. In this manner, injury to the person may be reduced. In one embodiment, the retention element comprises stitching through the adjacent portions of the folded extensible section. In another embodiment, the retention element comprises entangled interlocking fibers formed by needle punching adjacent portions of the folded extensible section. A safety strap can be provided in parallel with the energy absorbing element to carry the load if the energy absorbing element extends fully and breaks apart, minimizing the possibility of the support element ejecting from the vehicle. The extensible element in the contracted configuration, with the safety strap if present, can be packaged in a breakaway casing to keep the folds of the extensible section in the contracted configuration and to protect the energy absorbing element from inadvertent damage under normal conditions. In other aspects, the system can include a retraction mechanism located at an upper end of the suspension element. The support element can be constrained to move vertically by a vertical guide bar. The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: The disclosure of U.S. Provisional Patent Application No. 61/574,610, filed on Aug. 5, 2011, is incorporated by reference herein. During blast-induced motion of the vehicle, there are three phases of concern for the occupants: take-off, ejection, and landing. During the take-off phase, the vehicle realizes a sudden vertical velocity, while the occupants are essentially motionless, putting the vehicle on a collision course with the occupants. High vertical forces are placed on the occupants through, for example, their seats, as they are accelerated to the vertical speed of the vehicle. These large accelerations can cause considerable injury. As the occupants are forced upwardly during the take-off phase, the elastic load-carrying elements that carry their load store energy like a spring. This energy comes back out as the vehicle slows at the apex of its trajectory, and further accelerates the occupant upwardly relative to the vehicle, tending to eject the occupant. This upward motion continues until a) the force of gravity causes the occupant to descend, b) a restraining harness acts to hold the occupant down, c) the occupant hits the roof if there is one, or d) the occupant is ejected upwardly, possibly out of the vehicle, as in the case of the gunner. The softer the elastic elements are that support the occupant, the softer the initial take-off forces are, but the greater is the tendency for ejection. Once the vehicle reaches the apex of its trajectory, it begins to accelerate downwardly under the force of gravity until it hits the ground and comes to rest. This sudden stop (i.e. deceleration) on landing can also cause injury to the occupant. While advancements in seat design have reduced the effects of these three phases on the occupants, there are some exceptions. One exception is the gunner seat in a military vehicle, such as a high mobility multipurpose wheeled vehicle (HMMWV), that uses only webbing, for example, seat-belt webbing, to make and suspend the seat. More particularly, the typical gunner seat suspension system is formed of nylon or another polymer fiber rope and/or webbing, which offers some compliance during a blast event to help soften the acceleration delivered to the occupant. This compliance acts much like a spring and stores the energy as the occupant is driven down as a result of the sudden upward movement of the vehicle. The challenge in designing the compliance “spring” into the suspension ropes and webbing is that the stored energy tends to come out shortly after the blast, as the occupant tends to become weightless for a brief time and is propelled upwardly. Thus, a restraint strap is typically provided to keep the occupant from being launched upwardly after the initial vertical jump, but causing other injury. Thus, the desire to make the system more compliant, to better soften the initial acceleration, only works to worsen the launching effect; softer springs tend to store more energy. In addition, springs are not efficient energy absorbers because they do not absorb much energy at the start of the stroke, so there is wasted displacement that could be used to save the occupant. Accordingly, an energy absorbing system is provided to address this problem by introducing one or more energy absorbing elements, in the form of a constant load damping mechanism, into a suspension system for support elements such as seats or stretchers in vehicles. By way of explanation, the energy absorbing element herein is analogous to a single-direction “Coulomb damping” effect (a “Coulomb damper” or “C-Damper”) in series with the suspension elements, such as ropes and/or straps. A Coulomb damper is also typically referred to as a friction damping device, in which the relative motion of the damper initiates at a load level commonly referred to as the static friction value, and then holds a constant, possibly different, force as the device actuates, termed the dynamic friction value. The energy absorbing elements described herein for a suspension system do not necessarily use friction as the mechanism to resist motion, but they do approximate the behavior of a Coulomb damper in that they have an initiation load, and a nearly constant load as the energy absorbing element extends, described further below. In conjunction with the energy absorbing element, the remainder of the suspension system can be made as stiff as possible. That is, the suspension elements, the straps and/or ropes suspending the seat, can be formed to be as stiff as possible, like a stiff spring, to minimize the launching effect, and allow the energy absorbing element to provide the majority of the displacement at constant or near-constant restraining load. This effectively doubles the energy that is absorbed for a given displacement, without overloading the occupant. The energy absorbing elements store the energy in a non-conservative way, as, for example, broken fibers (described further below), not as a spring, so the energy cannot come back out into the system. One exemplary embodiment of the energy absorbing system 10 is illustrated in The energy absorbing system 10 includes an energy absorbing element 50 disposed in series with at least one of the suspension elements 42. Referring to In one embodiment, the retention element 68 is formed by stitching 67 that extends through adjacent portions 66 to hold them together in abutting relationship, indicated schematically in an expanded manner in In operation, when a blast event occurs beneath the vehicle, the vehicle is propelled upwardly, and the gunner seat and gunner are propelled upwardly as well. The retention element, for example, the stitching, in the extensible section of the energy absorbing element fails over a period of time, which allows the strap of the energy absorbing element 50 to extend and absorb energy as the gunner seat is propelled upwardly. In this manner, the load on the gunner is slowed at a nearly constant rate. In addition, the woven webbing, such as seat belt webbing, that forms the suspension elements and the extensible section can be formed to be as stiff as possible, which helps to minimize the launching effect and the return of energy to the system. Any number of folds can be provided, which can be readily determined by the expected loads for the application and the materials used. Any suitable stitching can be used. In a further embodiment, the retention element 68 is formed by needle punching or needle felting the adjacent portions 66 to hold them together in abutting relationship. A needle punch operation is performed by inserting a plurality of barbed needles, typically on a needle board, through the adjacent portions of the energy absorbing portion from one or both sides. The energy absorbing portion can be formed from a woven webbing, such as seat belt webbing, or other fibrous materials, including non-woven materials. The barbs on the needles catch fibers as the needles penetrate, pushing the fibers from one portion 66 through to an adjacent portion 66, entangling the fibers. The entangled fibers thereby become mechanically interlocked. The interlocked fibers hold together under normal loading conditions. The interlocked fibers are capable of pulling apart at a determined greater load, the initiation load, thereby absorbing energy while the extensible section 62 extends over time. The retention element can have other configurations. For example, the retention element can be formed from an adhesive, staples, or hook and loop type fasteners. Referring to The energy absorbing element can be connected in series with the suspension element in any suitable manner. In In The energy absorbing element 50 may also be encased in a breakaway casing 108 of, for example, a soft plastic, rubber, or cloth material, to keep the folds of the extensible section in the contracted configuration and protected from inadvertent damage and from getting in the way of the occupant. The casing readily rips open when the retention element of the energy absorbing element begins to fail. In some military vehicles for medical purposes, one or more stretchers are suspended from the ceiling of the vehicle. As noted above, during an under vehicle blast, the vehicle jumps up suddenly in the vertical direction. Such a sudden movement can place high acceleration (i.e., g) loads on the stretcher and stretcher occupant. These high loads are short in duration, but can injure the occupant of the stretcher when hung in the usual way. Other types of seats in military vehicles are often suspended by ropes in an attempt to mitigate the shock loading from a blast. These designs are also prone to the shortcomings of a spring-only system. The g load on the occupant continues to increase as the seat deflects. There is a tendency for the seat to spring back and throw the occupant after it deflects, and some of the ropes can lose tension and go slack allowing the seat to move in an uncontrolled manner. In addition, the ropes acting as springs are not optimum energy absorbers. Pre-tensioning of the ropes is used to help improve performance and minimize the potential for slack ropes, but the improvement is marginal. Such rope seat systems can be improved by using an energy absorbing element in the system as described above. For example, In another embodiment, illustrated in Operation of the energy absorbing system, as illustrated in of A simple model illustrates the advantage of the energy absorbing system for a gunner seat application. Two phases are modeled, the take-off phase, and the ejection phase without restraint. The unrestrained ejection height is used to gauge the tendency for ejection. In a base model (referring to Just after the blast, the vehicle is assumed to be in motion with upward velocity V0, but it has not yet displaced appreciably. Just after the blast the gunner is at rest. Since the mass of the vehicle is much greater than the mass of the gunner, in the model the motion of the vehicle is assumed to be unaffected by the gunner. The vehicle moves upwardly with initial velocity V0, and slows under the force of gravity, eventually returning to the ground where it is assumed to be at rest from that point on. The motion of the vehicle forms the forcing function for the system. Referring to Once the initial upward velocity of the vehicle V0 is given, the motion of the vehicle is prescribed. The vehicle's upward velocity is slowed under the force of gravity, and the vehicle returns to the ground. The motion of the suspended mass (the gunner) is solved for using a time stepping integration routine given the system parameters, and the motion of the vehicle. As an example, the following conditions were investigated for the base model without the energy absorbing element:
The transient results are shown in The same parameters were then investigated with an energy absorbing element added in series with the spring.
The transient results are shown in The energy absorbing system has been tested with a crew seat and a gunner sling seat. The energy absorbing system can provide surprisingly dramatic reductions. The energy absorbing system is effective in reducing adverse effects on occupants for all three phases of vehicle motion following an underbelly blast. During the take-off phase, the initial g loading on the occupant is greatly reduced. During the ejection phase, the tendency to eject the occupant is greatly reduced, making the use of a restraining harness safer and more effective. During the landing phase, if the energy absorbing element is not fully extended during the take-off phase, residual damping capability is available to soften the landing as well. It will be appreciated that features of the various embodiments and examples described herein can be combined in different ways from those explicitly shown and described. The invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. |