Title:
Energy absorber for counterbalance mechanism
Kind Code:
A1


Abstract:
An energy-absorbing device for use with a counterbalance mechanism to relatively harmlessly absorb energy potentially released should a component of the counterbalance mechanism fail. A frame is attached to a portion of the counterbalance mechanism and supports an impact receiving member, and a plurality of deformable support members. In the event of a failure in the counterbalance mechanism, a part of the counterbalance mechanism strikes a face of the impact receiving member. Deformable support members are attached to the opposing face of the impact receiving member and are deformed by the impact and thus absorb the energy that is transferred by the impact. The deformable support members and the impact receiving member are readily replaceable.



Inventors:
Zaerr, Jon Benjamin (Portland, OR, US)
Application Number:
11/590042
Publication Date:
06/19/2008
Filing Date:
10/30/2006
Assignee:
Gunderson, LLC
Primary Class:
International Classes:
B61D17/00
View Patent Images:
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Primary Examiner:
SMITH, JASON C
Attorney, Agent or Firm:
CHERNOFF, VILHAUER, MCCLUNG & STENZEL, LLP (PORTLAND, OR, US)
Claims:
What is claimed is:

1. An energy-absorbing device for use in connection with a counterbalance apparatus, comprising: (a) a base; (b) an impact receiving member having a first face and an opposite second face, the impact receiving member being supported in a location adjacent the base; and (c) a deformable support member attached to the impact member and interconnected with the base, the deformable support member being arranged to be deformed by an impact on the first face and thus to absorb energy from an impact on the first face of the impact receiving member.

2. The energy-absorbing device of claim 1, wherein the deformable support member is plastically deformed when absorbing the energy from the impact.

3. The energy-absorbing device of claim 1, wherein the base includes a collar defining an interior space and the impact receiving member is held within the interior space by the deformable support member prior to receiving an impact.

4. The energy-absorbing device of claim 1, wherein the deformable support member is U-shaped.

5. The energy-absorbing device of claim 1, including a plurality of the deformable support members, attached to the impact receiving member at apart-spaced positions.

6. The energy-absorbing device of claim 1, including a plurality of the deformable support members, each detachably attached to the base.

7. The energy-absorbing device of claim 1, wherein the deformable support member is fixedly attached to the impact receiving member.

8. The energy-absorbing device of claim 1, wherein the counterbalance apparatus includes a spring and a cable arranged to load the spring, and wherein the impact receiving member is located in a probable path of the spring should the cable fail under load.

9. A counterbalance apparatus, comprising: (a) a force-generating element and a tension-carrying member, the force-generating element being interconnected with the tension-carrying member; (b) a guide tube that at least partially surrounds a portion of the force-generating element and the tension-carrying member; (c) a collar mounted on an end of the guide tube; (d) an impact receiving member mounted adjacent the end of the guide tube, and having a first face directed toward the force-generating element and having an opposite second face; and (e) a deformable support member attached to the second face of the impact receiving member and interconnected with the collar, the deformable support member being arranged to absorb energy from and thus to be deformed by an impact of the force-generating element against the first face of said impact receiving member and thereby avoid damage to other portions of the counterbalance apparatus in event of a failure of the tension-bearing member.

10. The counterbalance apparatus of claim 9 including a plurality of the deformable support members, wherein the impact receiving member and the deformable support members are interconnected with the collar by fasteners whereby the deformable support members are replaceable.

Description:

BACKGROUND

The present disclosure relates to counterbalance mechanisms and in particular to a device for safely absorbing energy from a part of a counterbalance mechanism accidentally released by a failure of a part of such a counterbalance mechanism.

Counterbalance mechanisms have long been used to make it possible to raise heavy objects by providing a force in opposition to the weight of such a heavy object. The force provided by the counterbalance mechanism typically is slightly less than a load that is desired to be balanced so that the counterbalance mechanism supports a large part of the load in a static condition. Such an arrangement allows for the load to be easily moved by applying a small additional force, in comparison to the force that would otherwise be required to move the load without the counterbalance mechanism.

Counterbalance mechanisms have been used extensively in many mechanical devices, including lift bridges and the like. One such application is in a railroad freight car which has multiple decks that are capable of carrying cargo. U.S. Pat. Nos. 5,743,192, 5,794,537, and 5,979,335 disclose a multi-unit railroad freight car for carrying automobiles on multiple levels of decks. In each of the disclosed freight cars, a plurality of automobiles may be supported on decks that are adjustable in height. Each end portion of the middle level deck in each unit of the freight cars is mounted on a pivot axis at its inner end so that the outer end portion of the deck, located at the end of the car unit, may be raised and lowered to facilitate the loading and unloading of vehicles on the lowest level of the car.

In U.S. Pat. No. 7,055,441, the specification of which is incorporated herein by reference, a counterbalance mechanism allows a pivoted end portion of the middle level deck of such a railroad freight car to be raised and lowered easily by its operator. The counterbalance mechanism has an elongate tension-carrying member, coupled to the hinged end portion of the deck, that applies a lifting force from a spring to allow a person to raise the hinged end portion of the deck with mere hand pressure. The lifting force provided by the counterbalance mechanism assists the operator in raising the hinged end portion of the deck by carrying much of its weight as it is moved between its raised and lowered positions.

Such a counterbalance mechanism entails the risk that failure of a tension-carrying cable might free a powerful spring or a large counter-weight, causing damage to the counterbalance mechanism and potentially causing injury to an operator. In the event of a failure of the tension-bearing member, the counterbalance mechanism may release an amount of energy related to the force that was supporting the counterbalanced object, and a part of the counterbalance mechanism may be released to potentially cause structural damage and personal injury. The counterbalance mechanism for decks within a railroad freight car may be supporting more than a ton of weight, and the energy released if a failure occurs is potentially great.

The energy that is potentially freed as a result of a failure in the counterbalance mechanism, thus presents a risk of damage to the remainder of a counterbalance mechanism and the associated structure of the freight car, and a risk of injury to nearby personnel.

What is needed, then, is an energy-absorbing mechanism capable of absorbing a large portion of the energy that may be released in the event that a failure occurs in a counterbalance mechanism in a railroad freight car, so that the failure of the counterbalance mechanism will not result in structural damage to the railroad car or injury to nearby personnel.

SUMMARY OF THE DISCLOSURE

The mechanism disclosed herein answers the aforementioned needs by providing an energy-absorbing device as defined by the appended claims. In one embodiment such a device may be associated with a counterbalance mechanism, to protect a railroad car and nearby personnel from injury in case of a failure of the counterbalance mechanism.

In one embodiment the device disclosed includes a deformable support member that gives way in response to an impact resulting from a failure of a load supporting portion of a counterbalance mechanism. The energy-absorbing device is attached to a housing for a force-generating element of the counterbalance mechanism, such as a spring or a counterweight, and prevents a suddenly released force-generating element and force-transmitting member from damaging the structure of the freight car, by cushioning an impact and absorbing a large portion of the energy of the force-generating element.

One embodiment of the energy-absorbing device is associated with a counterbalance mechanism that supports a movable hinged end portion of a deck of a railroad freight car.

In one embodiment of the disclosed apparatus, the energy-absorbing device includes a blocking or impact receiving member mounted on a plurality of deformable support members. The impact receiving member is connected with a frame attached to an end of a housing for a movable part of the counterbalance mechanism. In the event of a failure, a released part of the counterbalance mechanism that moves toward the blocking or impact receiving member strikes the member on a face that is directed toward the interior of the housing. As a result of such an impact, the deformable support members are bent from their original configurations and thereby absorb the kinetic energy of the released part.

In one embodiment, the energy-absorbing device is attached to a housing for a moving portion of a counterbalance mechanism and includes attachment bars extending away from an end of the housing. The deformable support members may be of a “U” shape and may be located where they are urged to bend in response to collision of released parts of a counterbalance mechanism against an impact receiving member so that they absorb the energy from moving parts released by failure of a part of the counterbalance mechanism.

In one embodiment one end of each U-shaped deformable support member is attached to a side of the impact receiving member opposite a face which the moving force-generating element of the counterbalance mechanism would strike if set free as by a failed cable. The other end of each of the U-shaped deformable support members may be connected to the attachment bars by a detachable fastener such as a nut and bolt combination. This structure allows the deformed portion of energy-absorbing device to be replaced after an impact occurs, by simply detaching the deformable support members from the attachment bars.

In one embodiment of the energy-absorbing device the blocking or impact receiving member may be a plate in the shape of an annular ring defining a central opening through which a fitting attached to an end of the counterbalance mechanism may fit.

In one embodiment of the energy-absorbing device, the attachment bars are beveled to provide additional space into which the deformable support members may be deformed in order to absorb additional energy from a moving member of a counterbalance mechanism.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cutaway side elevational view of a portion of one unit of a multi-unit railroad freight car, showing a movable end portion of an automobile-carrying deck located in an upwardly inclined position.

FIG. 2 is an interior detail view, at an enlarged scale, showing the uppermost portion of one side wall of the body of the unit of a railroad freight car shown in FIG. 1, showing an end of a deck in a raised position, and also showing a counterbalance mechanism equipped with an energy-absorbing mechanism.

FIG. 3 is an isometric bottom view, at an enlarged scale, of the energy-absorbing mechanism shown in FIG. 2, also showing the bottom portion of a guide tube portion of the counterbalance mechanism.

FIG. 4 is an exploded isometric bottom view of the energy-absorbing mechanism shown in FIG. 3.

FIG. 5 is a sectional view, taken along line 5-5 of FIG. 3, showing a portion of the counterbalance apparatus in a lightly loaded condition within the guide tube.

FIG. 6 is a sectional view, taken along line 5-5 of FIG. 3, showing a portion of the counterbalance apparatus after having struck the energy-absorbing device and also showing the deformable support members in a deformed state.

FIG. 7A is a sectional view of the combination of one of the deformable support members and an alternative embodiment of an attachment bar.

FIG. 7B is a sectional view of the support member and attachment bar shown in FIG. 7A, showing the deformable support member in a deformed condition.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring to the drawings which form a part of the disclosure herein, FIG. 1 shows part of a car body 10 of one car unit of a multi-unit railroad freight car that incorporates an energy absorber for a counterbalance mechanism. The freight car may include two or more adjacent car units, and each respective car unit may include a cargo well 12, a middle deck 14, and an upper deck 16, for selectively supporting and storing automobiles 18 in a tri-level arrangement. Each deck preferably has a shape that provides ample strength for supporting automobiles 18, while providing sufficient space to accommodate automobiles 18 of various heights that the car is desired to carry.

As can be seen in FIG. 1, the automobiles 18 stored on the lowest level of the freight car body 10 rest in the respective cargo well 12 of each car unit. In order to maximize use of the available vertical space in the upper two cargo levels, the middle deck 14 is positioned where it would prevent the loading and unloading of automobiles 18 from the cargo well 12 were it not for a hinged end portion 20 of the middle deck 14 that may be selectively raised while automobiles 18 are loaded into or unloaded from the cargo well 12. It is to be understood that each of the car units may have a middle deck 14 and an upper deck 16, and that the middle deck 14 in each car unit may include a hinged end portion 20 at either or each end.

A respective counterbalance apparatus 22 is provided at each side of the car unit to carry part of the weight of the hinged end portion 20 so that it may be raised easily when necessary. The counterbalance apparatus includes an energy-absorbing device 24 in order to absorb energy that may be released should a failure of the counterbalance apparatus 22 occur and result a part of the counterbalance apparatus 22 being freed to move. The energy-absorbing device 24 prevents an impact of such a freed part of the counterbalance apparatus from causing substantial damage to the counterbalance apparatus 22 to an associated housing, or to the associated supporting structure of the freight car body 10. Furthermore, a portion of the energy-absorbing device 24 may be replaced after an impact and thus can reduce costs for repairs if a failure of the counterbalance apparatus 22 occurs.

Each counterbalance apparatus 22 may include a force-transmitting member, such as a cable 28 or chain (not shown) that interconnects and transmits forces between a counterbalanced object such as the hinged end portion 20 and a force-generating element, such as a spring 32 or a counterweight (not shown). The force-generating elements of the counterbalance mechanisms 22 together may generate a lifting force that is slightly less than the applied portion of the weight of the hinged end portion 20. Each force-transmitting member may include a first elongate tension carrying segment 34 operatively connected to, and extending upward from, the hinged end portion 20 and a second elongate tension carrying segment 36 operatively interconnected with the force-generating element so that tension in the first elongate tension carrying segment 34 is caused by tension in the second elongate tension carrying segment 36, which in turn is caused by the force-generating element.

In a simple counterbalance mechanism, the force-transmitting member may be a cable 28, and the force-generating element may include the spring 32. In that instance, it may be appropriate to include a direction changing force transfer device 42, including one or more sheaves 44, or other mechanisms such as bell cranks (not shown). The direction changing force transfer devices 42 may be positioned between the first elongate tension carrying segment 34 and the second elongate tension carrying segment 36. In a more complex counterbalance mechanism, an appropriate force-transmitting arrangement might include gears, rigid members, bell cranks, etc.

The middle deck 14 may be provided in the form of three segments arranged end-to-end, with the center segment fastened securely and tightly to the side posts 40 by bolts or other releasable but secure fasteners so that the middle deck 14 is incorporated structurally in, and adds rigidity to, the entire car unit as well as being solidly supported by the side walls 46.

Hinges 47 pivotally attach the hinged end portion 20 to two horizontal support beams 48 that extend longitudinally along the opposite side walls 46 of the car body 10 at equal heights and that are rigidly fastened to the side walls 46 by fasteners such as bolts. Each of the horizontal support beams 48 extends inwardly from the side walls 46, so that when the hinged end portion 20 is in a lowered position it is supported along its lateral margins by the horizontal support beams 48. In this manner, the horizontal support beams 48 support the portion of the weight of the hinged end portion 20 and any automobiles 18 or other cargo carried on the hinged end portion 20 in excess of the weight supported by the counterbalance apparatus 22. Each of the horizontal support beams 48 is positioned at a vertical height along its respective side wall 46 where the hinged end portion 20 abuts the fixed portion of the middle deck 14 at a pivot axis defined by the hinges 47 through which the inner end of the hinged end portion 20 is attached. The hinges may allow an outer end 50 of the hinged end portion 20 of the middle deck 14 to be raised as much as about 4 feet to an inclined position above the horizontal support beams 48. Raising the hinged end portion 20 of the middle deck 14 while it is empty allows automobiles 18 to be moved over the trucks 52 and the body bolsters 54 of the car body 10 and into or out of the cargo well 12 during loading and unloading of the freight car 2.

Referring to FIG. 2, the counterbalance apparatus 22 is used to support most of the weight of the hinged end portion 20 so that it may easily be raised and lowered manually. The counterbalance apparatus 22 applies a lifting force from the force-generating element to the outer end 50 of the hinged end portion 20 through a tension-carrying member, which may be, for example, a flexible 5/16″ diameter steel cable 28. The cable 28 operatively connects the hinged end portion 20 to the force-generating element and extends upward and around sheaves 44 which may be mounted in fixed locations, such as between the corner post 38 and the side post 40 that is next to the corner post 38 along the side wall 46 in the direction toward the mid-length of the car body 10.

Referring again to FIG. 2, the generally helical compression spring 32 or another force-generating element may be held in a protective housing such as a guide tube 56, securely mounted in the car body 10, where the compression spring 32 is free to extend and be compressed, or a counterweight is free to move up or down. The compression spring 32 and the guide tube 56 may also be located in an interior space that lies between the corner post 38 and the adjacent side post 40. In this way, the counterbalance apparatus 22 is situated in what is otherwise unused space inside the railroad car body 10 and does not interfere with any other structure or cargo inside the car.

The guide tube 56 comprises an interior liner sleeve 58 (shown in FIGS. 5-6), and an upper end fitting 60 that is securely connected to the guide tube 56, retains the upper end of the spring 32 and opposes the force of the cable 28 in order to compress the spring 32 and thus provides a force supporting part of the weight of the movable deck part 20. The sleeve 58 may be made from, or at least lined with, a layer of polymeric resin such as UHMW polyethylene so that friction and wear may be minimized as the compression spring 32 moves within the guide tube 56.

The upper fitting 60 defines an opening 62. The cable 28 extends through the opening 62 and through the compression spring 32, and is secured to a cable end fitting 64, as by being looped around a crosspin of the end fitting 64 and held by a swaged or cast cable fastener 66, shown in FIGS. 5-6.

Referring to FIGS. 5-6, the cable end fitting 64 is connected to the end of the spring 32 as by mating with a suitable spring retainer 68. The spring retainer 68 may, as shown, be in the form of a cup with a suitably sturdy annular bottom plate 70 and an upwardly extending sidewall 72 that surrounds a bottom end of the spring 32, so that the retainer 68 acts as a piston supporting the lower end of the spring 32 and guides the spring 32 as it moves within the guide tube 56. The end fitting 64 may have an upwardly projecting part that fits matingly through the central opening 74 in the bottom plate 70 and a radial flange 76, extending beneath the bottom plate 70, that is too large to pass through the opening 74. The sleeve 58 facilitates movement of the retainer 68 within the guide tube 56. Because of the arrangement of the cable 28, movement of the hinged end portion 20 up or down causes the retainer 68 to slide oppositely within the sleeve 56. Movement of the retainer 68, in turn, compresses the compression spring 32 or allows it to expand downward beneath the upper fitting 60, depending on the direction in which the retainer 68 is moving.

The length of the cable 28 and the force of the compressed spring 32 may be such that when the hinged end portion 20 is in the lowered position the compression spring 32 applies a lifting force to the hinged end portion 20 that is slightly less than that which would lift the outer end 50 of the hinged end portion 20. It will be understood that the compression spring 32 should be long relative to the distance through which given a point on the cable 28 will travel when the hinged end portion 20 of the middle deck 14 is raised or lowered, so that the magnitude of the lifting force supplied by the counterbalance apparatus 22 remains within a small range during raising and lowering of the hinged end portion 20. The hinged end portion 20 of the middle deck 14 can thus be raised easily during loading of automobiles 18 into the cargo well 12 to provide ample overhead clearance above the body bolster 54 as automobiles pass over the wheeled truck 52 at each end of the multi-unit freight car or over a shared truck between car units.

FIGS. 2-6 show the energy-absorbing device 24 that is used to absorb the energy from a spring 32 or other force-generating element released by a failure in the counterbalance apparatus 22 such as a failure of the cable 28. Such a released spring 32 would result in an impact of the retainer 68 against the energy-absorbing device 24. If the cable 28 should fail, the spring 32 would rapidly expand from a compressed condition between the upper fitting 60 and the retainer 68, launching itself, the spring retainer 68, the end fitting 64, and any attached portion of the cable 28 downward through the guide tube 56 toward the energy-absorbing device 24. The energy-absorbing device 24 helps to prevent substantial damage from occurring to the guide tube 56 and helps to prevent injury from occurring to an operator who may be manually lifting the hinged end portion 20 of the middle deck 14. The energy-absorbing device 24 may be constructed as shown, to include energy-absorbing parts that are easily replaced after an impact occurs. The construction of the energy-absorbing device 24 also allows for ready access to the interior of the guide tube 56 so that repairs may be made to the spring 32 or cable 28.

Referring now to FIGS. 3 and 4, as depicted, the energy-absorbing device 24 is attached to the lower end of the guide tube 56 and includes a base that may be in the form of a collar 82, which may be welded to the guide tube 56, and a plurality of attachment bars 84, each securely attached as by being welded to or formed as an integral part of the collar 82. In one embodiment, the collar 82 is welded or otherwise fixedly attached to the guide tube 56; however, it will be understood that the collar 82 may be detachable so long as it is capable of withstanding the maximum anticipated amount of energy from a potential impact of a released part of a counterbalance mechanism without separating from the guide tube 56.

A first, or outer, end of a deformable support member 86 is detachably connected to each attachment bar 84 as by a fastener such as a bolt and nut combination 88. Each deformable support member 86 is a metal strap bent into a “U” shape, with the second end 90 of the strap, which may be wider than the first or outer end, being attached to an impact receiving, or blocking member 92 that fits within or is aligned with the lower end of the guide tube 56 to block, or close, that end of the guide tube 56 and thus safely contain the spring 32, the spring retainer 68, and the end fitting 64 in the case of a cable failure.

The impact receiving member 92 and the guide tube 56 are similarly shaped, and the impact receiving member 92 has a slightly smaller size than the interior of the guide tube 56, so that it fits within the guide tube 56. For example, the guide tube 56 and impact receiving member 92 may be of a cylindrical shape, in which case the diameter 93 of the impact receiving member 92 is slightly smaller than the internal diameter of the guide tube 56, and the impact receiving member 92 may fit within the interior of the guide tube 56, loosely enough not to jam in the collar 82 when struck by a released part of the counterbalance mechanism, as shown in FIGS. 5 and 6.

The impact receiving member 92 may be of flat plate steel in the form of an annular ring that defines a central hole 94, as shown in FIG. 4. The impact receiving member 92 has an upper, or first face 96 and a lower, second face 98. The radial distance between the central hole 94 and the exterior margin is designed to provide room for attachment of the upper end 90 of each deformable support member 86. The upper ends 90 of the deformable support members 86 may be attached as by being welded, to the second face 98 in uniformly spaced-apart positions about the central hole 94. A pair of mounting ears 100 are attached to the second face 98 of the impact receiving member 92, aligned with each other on opposite sides of the central hole 94 along an imaginary diametric line across the annular plate 92, as shown in FIGS. 3 and 4. Each mounting ear 100 is located between two deformable support members 86 in one embodiment.

A stopper bar 102 is attached to the ears 100, extending along the diameter of the impact receiving member 92 and between the ears 100, attached, for example, by bolt and nut combination 101. The stopper bar 102 thus extends across the hole 94 as shown in FIG. 3, at a location spaced a small distance beneath the lower face 98, leaving room for the cable end fitting 64 to protrude through the central hole 94 when the bottom plate 70 of the retainer 68 contacts the annular impact receiving plate member 92. The length of the stopper bar 102 is slightly less than the diameter of the interior of the guide tube 56 so that the stopper bar 102 fits within the guide tube 56, as shown in FIG. 3.

The deformable support members 86 may be of any configuration that is capable of bending in response to an impact against the impact receiving plate 92 and thus absorbing energy from the moving spring 32 or a counterweight from a counterbalance mechanism. As shown in FIGS. 3 and 4, the deformable support members 86 may be of steel plate cut to a slender flat bar shape and bent to be generally “U” shaped, so that each deformable support member 86 includes an attached or upper end 90, a U-shaped central portion 104, and the detachable end 106. The U-shaped central portion 104 of the deformable support member 86 extends away from the second or lower face 98 of the annular blocking member 92. The detachable end 106 of the deformable support member 86 extends parallel with the attached end 90 generally toward the second face 98 of the impact receiving element 92 at a location radially further outward from the central hole in the annular impact receiving member 92, but it does not extend the entire distance back to the second face 98. The detachable end 106 of the deformable support member 86 defines a hole 108 that is aligned with a hole 110 defined in the lower portion of the attachment bar 84 when the annular impact receiving member 92 is fitted within the collar 82. The nut and bolt combinations 88 thus detachably attach the disposable and replaceable part of the energy-absorbing assembly 24 to the collar 82.

FIGS. 3 and 4 show that four deformable support members 86 are used, although it will be understood that any convenient number of deformable support members 86 suitable to absorb the anticipated amount of energy from the counterbalance mechanism may be used with an equal number of attachment bars 84. The embodiment shown in FIGS. 3 and 4 has deformable support members 86 evenly spaced apart around the interior perimeter 100 of the annular ring 96 so that each deformable support member 86 is located to absorb a substantially equal amount of energy if an impact occurs.

Referring again to FIGS. 5 and 6, the energy-absorbing device 24 is attached to one end of the guide tube 56 as by welding the collar 82 to the guide tube 56 adjacent its lower end, where the energy absorbing device can block a released portion such as the spring 32 and cable 28 of a counterbalance mechanism, and receive the impact of a released part in the event that a failure occurs in the counterbalance apparatus 22. The force-generating element fits within the spring retainer 68 and drives the retainer 68 through the guide tube 56. The end fitting 64 may be smaller than the central opening 94 in the annular impact receiving plate member 92 and fits through the central opening 94 if the spring 32 is released by failure of the cable 28 and drives the retainer 68 against the annular impact receiving member 92. The end fitting 64 can then strike and perhaps be contained by the stopper bar 102.

Referring to FIG. 6, in the event of a failure, the retainer 68, driven by the spring 32, impacts the annular impact receiving plate element 92 and the end fitting 64 passes through the central hole 94 defined in the annular impact receiving plate member 92. In response to the impact, the deformable support members 86 flex and are plastically deformed to absorb much of the energy transferred from the spring 32 by the impact. The material of which the deformable support members are made is malleable enough to absorb the maximum energy caused by such an impact by bending, rolling the “U” bend along the straplike deformable members 86, rather than fracturing. Any parts, such as the end fitting 64, that pass through the central opening 94 in the impact receiving member 92 will contact the stopper bar 102 and thus be kept from simply passing freely out from the guide tube 56.

Referring now to FIGS. 7A and 7B, the interior surface 114 of the lower portion of each attachment bar 84 may be beveled. The beveled end 114 creates additional space into which for the deformable support members 86 can deform in the event an impact occurs, as shown in FIG. 7B. In a pre-impact condition, as shown in FIG. 7A, a portion of the detachable end 106 of the deformable support member 86 is not in contact with the beveled end 114. When an impact occurs, the deformable support member 86 may flex to deform a greater distance in a radial direction as compared to a deformable member 86 supported by an attachment bar 84 with a non-beveled end.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.