Patent Description:
Truck Mounted (and towable) Attenuators (TMAs) have been used for many years on our nation's highways to protect road workers in works zones and other areas adjacent to high speed traffic. These crash attenuators, otherwise referred to as crash cushions, are typically mounted to the back of a work truck or other shadow vehicle, or towed thereby, and then placed some distance behind the work being done. In this way the crash cushion protects the road workers from errant vehicles that may have left the open travel lanes and would otherwise endanger the road workers. Likewise there may be road maintenance operations that require a slow moving shadow vehicle that is driven by one of the road workers. In this instance, the driver of the shadow vehicle is also protected by the Truck Mounted attenuator, should a vehicle impact it.

The road workers are not the only ones deriving benefits from a TMA. Drivers of errant vehicles also benefit, as the impact with the crash cushion may lessen the potential injuries from such an impact.

<CIT> discloses a crash attenuator having a first frame member and a second frame member rigidly connected with a hinge assembly in a pre-impact configuration. The first and second frames are hingedly connected with the hinge assembly in an impact configuration, wherein the hinge assembly comprises a living hinge when the hinge assembly is in the impact configuration.

The present invention is defined by the following claims, and nothing in this section should be considered to be a limitation on those claims.

The present invention relates to a crash attenuator as defined in claim <NUM>.

The various embodiments of the crash attenuator provide significant advantages over other crash attenuator systems. For example and without limitation, the frames can be easily and quickly assembled with a minimum of parts, with the hinge assemblies providing both the rigid connection of the frame members during normal operation, and also providing a hinge, allowing for collapse of the attenuator, during an impact event. The frames can be easily and quickly replaced. At the same time, the configuration of the fastener opening and slot provide a controlled and consistent release force during an impact event.

The various preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

Referring to <FIG> and <FIG>, it should be understood that the term "longitudinal," as used herein means of or relating to length or the lengthwise direction <NUM> between an impact end <NUM> and an attachment end <NUM>, <NUM> of a crash attenuator <NUM>, <NUM>, and is aligned with and defines an "axial impact direction" which is generally parallel to the direction of traffic flow. The term "lateral," as used herein, means directed between or toward (or perpendicular to) the sides of the crash attenuator in a sideways direction <NUM>. The term "front," "forward," "forwardly," and variations thereof refer to the position or orientation relative to the attachment end <NUM>, <NUM>, which connects the crash attenuator <NUM>, <NUM> to a shadow vehicle <NUM> or the like, while the term "rear, "rearward," "rearwardly," and variations thereof refer to the position or orientation relative to the impact end <NUM> of the crash attenuator <NUM>, which receives an impacting vehicle <NUM>. The term "downstream" refers to the position or orientation moving away from the impact end <NUM> and toward the attachment end <NUM>, <NUM> of the crash attenuator <NUM>, while the term "upstream" refers to the position or orientation moving toward the impact end <NUM> and away from the attachment end <NUM>, <NUM> of the crash attenuator <NUM>. Therefore, for example, a component positioned downstream of another component is closer to the attachment end <NUM>, <NUM>, and vice versa, a component positioned upstream of another component is closer to the impact end <NUM>. The term "outboard" refers to the direction or orientation towards the outermost edges of the crash attenuator <NUM>, <NUM>, while the term "inboard" refers to the direction or orientation away from the outermost edges and towards the center of the crash attenuator <NUM>, <NUM>. The term "upper" refers to the vertical direction or orientation towards the top most edge of the crash attenuator <NUM>, <NUM>, while the term "lower" refers to the vertical direction or orientation towards the ground. The term "coupled" means connected to or engaged with, whether directly or indirectly, for example with an intervening member, and does not require the engagement to be fixed or permanent, although it may be fixed or permanent, and includes both mechanical and electrical connection. It should be understood that the use of numerical terms "first," "second" and "third" as used herein does not refer to any particular sequence or order of components; for example "first" and "second" frame members may refer to any sequence of such frame members, whether end, side, or mid frame members. The term "frangible," as used herein means to break into two or more pieces. The term "yield" means to bend or deform, without breaking.

<FIG> shows a crash attenuator <NUM> attached to a shadow vehicle <NUM>, wherein the weight of the crash attenuator <NUM> is supported and carried by the shadow vehicle <NUM>. As shown in <FIG>, the crash attenuator <NUM> is supported by a pair of wheels <NUM> rotatable on an axle. The attachment end <NUM> includes a lunette eye <NUM>, or pintle ring, that may be engaged by a pintle hook mounted on the shadow vehicle <NUM> (shown in <FIG>). In both embodiments of <FIG> and <FIG>, the crash attenuator <NUM>, <NUM> includes a frame defining a rear bay <NUM> and a front bay <NUM>. The rear bay <NUM> includes an impact frame member <NUM> and a rear mid frame member <NUM> connected by side frame members <NUM>, otherwise referred to as arm assemblies. Cartridges <NUM> and <NUM> are disposed inside of rear bay <NUM>. Front bay <NUM> is composed of a front mid frame member <NUM> and a backup frame member <NUM> connected by side frame members <NUM>, otherwise referred to as arm assemblies. Cartridge <NUM> is disposed inside of front bay <NUM>. It should be understood that the cartridge <NUM>, <NUM> and <NUM> are also disposed in the bays <NUM>, <NUM> of the crash attenuator <NUM> shown in <FIG>, but have been omitted in the drawings for the sake of clarity in showing the frame structure of that embodiment. It should also be understood that only a single cartridge, or more than two cartridges, may be disposed in the rear bay <NUM>, and the front bay <NUM> may be configured with two or more cartridges.

Of course it should be understood that a wide range of changes could be made to embodiments described above. For instance, the crash attenuator may be formed into more than two bays and each bay could have one, many, or no cartridges disposed within it. Likewise, the crash attenuator may also be designed as described in <CIT>, where the attenuator does not hinge between bays, but instead hinges at the back of the support vehicles. Other embodiments would take the form of a trailer attenuator <NUM> as shown in <FIG>, and/or as described in <CIT>, or a single bay with an attached cartridge, as described in <CIT>.

In preferred embodiments, frame members <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are constructed from welded steel, including structural steel tubing, plate, angle, and other steel shapes as appropriate. Other embodiments may use other structural materials for these elements, such as aluminum, plastics, fiberglass, and etc. In preferred embodiments, cartridges <NUM>, <NUM>, and <NUM> are made from aluminum cells, for instance as was described <CIT> and <CIT>. Other embodiments may use other appropriate crushable materials such as steel sheet, tin plated steel, plastic, or cardboard covered with an appropriate shell.

As shown in <FIG>, the crash attenuator <NUM> includes hinge assemblies <NUM> which join rear mid frame member <NUM> to front mid frame member <NUM>. Hinge assemblies <NUM> have a rotation axis <NUM>. The rear bay <NUM> rests on bumpers <NUM> when it has rotated approximately <NUM> degrees around rotation axis <NUM>. Fasteners <NUM> join side frame members <NUM> to impact frame member <NUM> and rear mid frame member <NUM>. Fasteners <NUM> also join side frame members <NUM> to front mid frame member <NUM> and backup frame member <NUM>.

<FIG> is a detail view of the connection of side frame members <NUM> and <NUM> to mid-frame members <NUM> and <NUM> shown in the embodiment of <FIG>. The mid frame members <NUM>, <NUM> of the crash attenuator <NUM> are coupled with cross members <NUM>, for example by welding, so as to define a center frame member <NUM>. The ends of the mid frame members <NUM>, <NUM> are joined with upper and lower box end brackets <NUM>, each having upper and lower walls <NUM>, <NUM> joined with side walls <NUM>, <NUM>. The side walls <NUM>, <NUM> are angled to form an angle α therebetween, which ensures that frame members <NUM>, <NUM> defining the side frame members <NUM>, <NUM> that are attached to the side walls are angled relative to each other, which promotes hinging of various hinge assemblies and subsequent collapse of the crash attenuator frame as further explained below. In one embodiment, the angle α defined between the side walls <NUM>, <NUM> is <NUM> degrees, although it should be understood that other embodiments may use angles that are greater or lesser than <NUM> degrees.

In the embodiment of <FIG> and <FIG>, the mid frame members <NUM>, <NUM> are connected with the hinge assemblies <NUM>, with separate upper and lower end brackets <NUM> connected to the ends of the mid frame members <NUM>, <NUM>. The end brackets <NUM> have upper and lower walls <NUM>, <NUM> joined with outer side walls <NUM>, <NUM>. The inner edges of the upper and lower walls are configured with upturned and downturned flanges <NUM>, <NUM> that abut when the crash attenuator is in the deployed configuration. The side walls <NUM>, <NUM> are angled to form an angle α therebetween, which ensures that frame members <NUM>, <NUM> defining the side frame members <NUM>, <NUM> are angled relative to each other, which promotes hinging of various hinge assemblies and subsequent collapse of the crash attenuator frame as further explained below. In one embodiment, angles α is <NUM> degrees, although it should be understood that other embodiments may use angles that are greater or lesser than <NUM> degrees.

Side frame members <NUM> and <NUM> include frame members <NUM>, configured and otherwise referred to as forward tubes, joined with frame members <NUM>, configured and otherwise referred to as rear tubes, with hinge assemblies <NUM>, including outer hinge members <NUM> and inner hinge members <NUM>, configured as bent steel plates overlapping the first and second frame members. It should be understood that the frame members <NUM>, <NUM> may be the same, or different lengths, for example with forward frame members <NUM> being shorter or longer than rear frame members <NUM>. In one embodiment, the outer hinge members <NUM> may be made from a thinner (or different) material than the inner hinge members <NUM>, and are configured as plates in one embodiment. Although two hinge members <NUM> and <NUM> are shown in <FIG> and <FIG>, it should be understood that some designs may only contain one hinge member, for instance, by eliminating either outer hinge member <NUM> or inner hinge member <NUM>. As show in the embodiment of <FIG>, the inner plates <NUM> are longer than the outer plates <NUM>, with each of the plates being wider at the junction between the first and second frame members <NUM>, <NUM>, e.g., at the virtual hinge axis.

Vertical members <NUM> join corresponding pairs of frame members <NUM> and frame members <NUM>, giving the side frame members <NUM>, <NUM> additional rigidity and constraining/spacing top tube members relative to bottom tube members. The various elements of the side frame members <NUM>, <NUM> are held together by welding, however other methods of assembly including bolting, riveting, brazing, and etc. may be used. Although the vertical members <NUM> are beneficial in many designs, there are other designs that may make use of additional vertical members, or no vertical members at all, resulting in two separate pairs of arm members. There may also be designs that make use of angled members, as disclosed in <CIT>. It should also be understood that other types of structural elements may be substituted for tubes <NUM>, <NUM>, and <NUM>, such as angles, round sections, C-channels, T-sections, I-sections, Σ-sections and etc. It should also be understood that other shapes or materials may be used for hinge members <NUM> and <NUM>.

Referring to <FIG>, the ends of the frame members <NUM>, <NUM> are joined to the frame members <NUM>, <NUM> and <NUM> with hinge assemblies <NUM>, <NUM>, each configured with an inner release plate <NUM>, <NUM> laterally spaced apart from an outer hinge plate <NUM>, <NUM>, for example by a distance equal to the thickness of the frame member <NUM>, <NUM>. It should also be understood that in some embodiments, release plates and hinge plates could be integrally formed with the first and second frame members <NUM> and <NUM>, for example by extending a side wall thereof.

Referring to <FIG> and <FIG>, which shows the hinge assemblies joining the mid frame members <NUM>, <NUM> or central frame member <NUM>, to the frame members <NUM>, <NUM>, each of the release plates and hinge plates are configured with first and second flanges <NUM>, <NUM>, <NUM>, <NUM>, with the first flanges <NUM>, <NUM> fixedly connected to opposite first and second sides of the frame members <NUM>, <NUM>, for example by welding, or with fasteners such as bolts. As mentioned, the first flanges may be integrally formed as a side wall of the frame members. The first flanges <NUM>, <NUM> are parallel as shown in <FIG> and <FIG>. The second flanges <NUM>, <NUM> are secured to the side walls <NUM>, <NUM>, <NUM>, <NUM> of the end brackets <NUM>, <NUM>, which are secured to and define a portion of the mid frame members <NUM>, <NUM> and or central frame member <NUM>. The second flanges <NUM>, <NUM> are substantially flush relative to each other, and are orthogonal to the first flange <NUM>, <NUM>. In other embodiments, the second flanges are oblique relative to the first flanges, meaning they are neither orthogonal nor parallel to the first flanges. Rather, the second flange of the hinge plate extends outwardly from the first flange (and away from the release plate) and forms an angle, for example, of <NUM> degrees relative thereto, while the second flange of the release plate extends inwardly from the first flange (and away from the hinge plate) and forms an angle, for example of <NUM> degrees relative thereto. It should be understood that other angles may also be suitable, and are defined by the relative angle of the frame members <NUM>, <NUM> to the end bracket side walls <NUM>, <NUM>, <NUM>, <NUM>, which define in part the frame members <NUM>, <NUM>, <NUM>. For example, in one embodiment, where the side walls are angled relative to each other, the first and second flanges are orthogonal in the pre-impact configuration.

Referring to <FIG> and <FIG>, which shows the hinge assembly <NUM> joining one side of the backup frame member <NUM> to the frame members <NUM>, <NUM>, the release plate <NUM> is again configured with first and second flanges <NUM>, <NUM>, with the first flange <NUM> fixedly connected to an inner sides of the frame members <NUM>, <NUM>, for example by welding, or with fasteners such as bolts. As mentioned, the first flange may be integrally formed as a side wall of the frame members. It should be understood that a hinge assembly <NUM>, with a release plate <NUM>, may also join the end impact frame member <NUM> to the frame members <NUM>, <NUM>. The hinge plate <NUM> is configured as a flat plate, but may be thought of as having first and second flanges <NUM>, <NUM> that are parallel and flush, with the first flange <NUM> being the portion overlying the frame member <NUM>, <NUM>, and the second flange <NUM> being the portion overlying the ends of the frame members <NUM>. Or, the hinge plate <NUM> may be bent, with first and second flanges. The first flanges <NUM>, <NUM> of the hinge and release plates are parallel as shown in <FIG>. The second flanges <NUM>, <NUM> of the hinge plate and release plate are secured to the frame members <NUM>. The second flanges are substantially orthogonal relative to each other, but with the second flange <NUM> of the release plate extending inwardly from the first flange (and away from the hinge plate) and forming an angle of <NUM> degrees relative thereto, so as to mate with end portions of the frame member <NUM>. In other embodiments, the flanges of the release plate may form an angle of <NUM> degrees relative to each other. It should be understood that other angles may also be suitable, and are defined by the relative angle of the frame members <NUM>, <NUM> to the end frame members <NUM>. The release plate <NUM> further includes a gusset plate <NUM>, or stiffening rib, fixedly coupled to the first flange, for example by welding <NUM>, and extending inwardly therefrom, preferably with an orthogonal relationship. The gusset flange has a triangular shape, with an angled side edge <NUM> and an end free edge <NUM>, which is disposed along a slip surface <NUM> of the second flange <NUM>.

As shown in <FIG> and <FIG>, the welding <NUM> extends along the length of the interface between the gusset plate <NUM> and the face of the first flange <NUM>, and along a portion of the interface between the gusset plate <NUM> and the second flange <NUM> between the junction of (corner between) the first and second flanges and an indicator notch <NUM>. In this way, the assembler knows to run the weld line up to the notch <NUM> and provides certainty as to the amount of weld provided between the gusset plate <NUM> and second flange <NUM>. This leaves a length (L) defining the free edge <NUM> of the gusset plate <NUM> abutting the second flange <NUM>, which is not welded or otherwise fixed, and which is measured between the notch and the end of the gusset plate <NUM>. In operation, the unfixed portion, or free edge <NUM>, of the gusset may abut and bear against the second flange <NUM> in compression so as to prevent and limit any inward bending of the frame member <NUM> relative to the end frame <NUM>. The gusset assists in making the connection more robust over the life of the system, for example resisting relative movement during vehicle turning and/or when the system is folded during transport. Conversely, the portion of the weld between the gusset plate <NUM> and second flange <NUM> may tear during an impact event so as to allow the first and second flanges <NUM>, <NUM> to bend relative to each other. It should be understood that gussets may also be provided at the connections between the flanges <NUM>, <NUM>, including welding portions thereof as described herein.

The second flange <NUM>, <NUM> of each hinge plate <NUM>, <NUM> is fixedly (non-releasably) secured to the end bracket/mid frame members or end frame members <NUM>, <NUM> with fasteners extending through mounting holes <NUM> to allow fasteners <NUM> to attach the side frames <NUM>, <NUM> to the mid frames. In one embodiment, the fasteners <NUM> are configured as bolts secured with nuts. Other embodiments may use other assembly methods, such as riveting welding, brazing, and etc. instead of bolts.

Referring to <FIG>, the second flange <NUM>, <NUM> of the release plates <NUM>, <NUM> are releasably secured to the end brackets <NUM>, <NUM>, which define in part the mid frame members <NUM>, <NUM>, center frame member <NUM>, or end frames <NUM> with fasteners <NUM> extending through mounting holes <NUM> (shown in <FIG>) to allow fasteners <NUM> to attach the side frames <NUM>, <NUM> to the mid frame members or end frame members. The mounting holes <NUM> include a fastener opening <NUM> and a slot <NUM> extending between the fastener opening and an inner side edge <NUM> of the release plate. The fasteners <NUM> are configured as bolts having a head <NUM> and a shank <NUM>, with the shank being inserted through the fastener opening and engaged with a nut <NUM>. A backing washer <NUM> is disposed between the head <NUM> and a "slipping" surface <NUM>, <NUM> of the second flange <NUM>, <NUM>. Preferably, the washer <NUM> is round, or circular, such that it offsets the points of the head <NUM>, which may have a hex shape, from the surface of the release plate. In this way, the washer <NUM> ensures that the orientation of the head will not require indexing for the slipping function to remain constant. The washer <NUM> may be configured as a split lock washer.

The shank <NUM> has an outer diameter allowing for it to pass through the fastener opening <NUM>, having an inner diameter D. The slot <NUM> has a width W defined between the opposite side edges <NUM>, <NUM> thereof, with the width W being less than the inner diameter D and outer diameter of the shank in one embodiment. In other embodiments, the width W and inner diameter D may be the same. In one embodiment, W is a <NUM> (<NUM>/<NUM> inch) while D is <NUM> (<NUM>/<NUM> inch) or <NUM> (<NUM>/<NUM> inch). The fastener opening <NUM> has a central axis <NUM>. The slot <NUM> communicates with the fastener opening <NUM> offset from the central axis <NUM>. In one embodiment, one side edge <NUM> of the slot defines a tangent to the outer edge of the fastener opening <NUM>. In this embodiment, the fastener opening <NUM> and slot <NUM>, in combination, are P shaped, or define a P-shaped release opening. As shown in <FIG>, each release plate <NUM>, <NUM> has a pair of fastener openings <NUM> and slots <NUM>, although it should be understood that a single fastener opening and slot, or more than two fasteners openings and slots, may be suitable. As show in <FIG>, the upper mounting hole <NUM> has the slot <NUM> oriented along a bottom of the opening <NUM>, while the lower mounting hole <NUM> has the slot <NUM> oriented along a top of the opening <NUM>, with the distance between the slots <NUM> thereby being minimized. By having the slots offset from the opening centerline and oriented on opposite sides thereof, the fasteners will not tend to both work their way out of the slots, for example if they became inadvertently loosened. It should be understood that the orientation may be switched, with the distance between the slots <NUM> being maximized, or the slots may be arranged along some other portion of the openings, for example along a midpoint thereof.

The fasteners may be torqued, and have a predetermined coefficient of friction, or range thereof, between the washer and release plate to assist in providing a controlled and consistent release force during an impact event. For example and without limitation, in one embodiment, the coefficient of friction (e.g., µ =. <NUM>) is between powder-coated steel (coated, or painted steel), which provides a desired static coefficient of friction. In combination with the coefficient of friction, the controlled clamping pressure between the components, in the form of torque applied to the holding fasteners <NUM>, provides a stable system during the life of the product by holding the arms in their pre-impact state. The torque and coefficient of friction, also help to ensure the release of the arms during impact. In one embodiment, the fasteners <NUM> securing the hinge plates are torqued to <NUM>-<NUM> (<NUM>-<NUM> ft lbs), while the fasteners <NUM> securing the release plates are torqued to <NUM>-<NUM> (<NUM>-<NUM> ft lbs). It should be understood that the number and dimensions of the fasteners <NUM>, the relative dimension of the slots <NUM> and fasteners <NUM>, the type and thickness of the material of the release plates, the torque applied to the fasteners, and many other variables may play a role, and may be varied, to allow the system to collapse at various predetermined impact forces and angles.

Although rear frame members <NUM> and front frame members <NUM> are shown as being similar in length in the embodiments of <FIG> and <FIG>, it should be understood that these frame members could be different in length depending upon the needs of a specific design. For instance, in some designs of side frame member <NUM>, front frame members <NUM>, or tubes, may be longer or shorter than rear frame members <NUM>, or tubes. Other designs may vary the length of the frame members of the front frame member <NUM> and still other designs may vary the length of both sets of frame members.

As shown in <FIG> and <FIG>, rear frame members <NUM> are angled from a longitudinal direction <NUM> by the angle β. Likewise, front frame members <NUM> are angled from a longitudinal direction <NUM> by the angle φ. In this way, the front and rear frame members form an obtuse angle therebetween. Angling the frame members, or arms, as shown in <FIG> and <FIG> promotes hinging of the hinge assemblies and subsequent collapse of the crash attenuator frame. Angling the frame members also promotes hinging of the inner hinge plate <NUM> and failure of outer hinge member <NUM>. In the embodiments of <FIG> and <FIG>, angle β is <NUM> degrees, although it should be understood that other embodiments may use angles that are greater or lesser than <NUM> degrees. It should also be understood that some embodiments may use angles that are unequal, for instance, angle β could be greater than angle φ, or vice versa.

Although the release plates <NUM>, <NUM> include release slots <NUM>, other methods could be used to provide weakened regions to promote the release of the fasteners <NUM>, as is needed in certain designs. For instance, the material and/or thickness of the release plate may be different than the material and/or thickness of the hinge plate <NUM>, <NUM>. <FIG> and <FIG> and <FIG> are sequential views of one embodiment of hinge assemblies <NUM> moving between a pre-impact configuration and an impact configuration during a vehicle impact.

Referring to <FIG>, the impact causes relative rotation of arms <NUM> and <NUM>, which creates tensile forces in outer hinge member <NUM> and compressive forces in inner hinge member <NUM>. Because outer hinge member <NUM> is made of thinner material, the tensile forces cause higher stresses in outer hinge member <NUM> than are present in inner hinge member <NUM>. This causes outer hinge member <NUM> to fail and break into two pieces. Meanwhile, inner hinge member <NUM> has formed a living hinge, allowing the rotation of rear tube <NUM> in relation to front tube <NUM>. The phrase "living hinge" refers to an integral piece of material having an intermediate region that flexes, including for example and without limitation, a thin flexible plate having opposite end portions and an intermediate portion. The hinge member may be thinned or cut to allow the rigid pieces to bend along the line of the hinge.

<FIG> and <FIG> shows hinge assemblies <NUM> in an initial, pre-impact condition or configuration. In <FIG>, mid frame members <NUM>, <NUM>, or central frame member <NUM>, move, or begin to rotate relative to the frame members <NUM>, <NUM> due to an impact by a vehicle into crash attenuator <NUM>, <NUM>, as shown in <FIG>. The impact causes rotation of the front and rear frame members <NUM>, <NUM> relative to the frame members <NUM>, <NUM>, <NUM>, <NUM>. The rotation of frame members <NUM>, <NUM>, as shown in <FIG>, causes the release plates <NUM> to bend/deform, and open up, with the first flange <NUM> moving relative to the second flange <NUM>. The tensile force applied to the release plate <NUM> causes the washer <NUM> to slide along the slip surface <NUM> of the release plate and the fastener shank <NUM> to pull through the slot <NUM> and eventually release the release plate <NUM> from the frame member <NUM>, <NUM>, <NUM> (see <FIG>), thereby allowing the hinge plate <NUM> to bend/deform and function as a living hinge. <FIG> shows the frame members at the end of the crash event, where the hinge plates <NUM>, defining living hinges, in the hinge assemblies permit continued rotation of rear and front frame members <NUM>, <NUM>.

During the same impact event, the rotation of frame members <NUM>, <NUM>, as shown in <FIG>, causes the release plates <NUM> to bend/deform, and open up, with the first flange <NUM> moving relative to the second flange <NUM>. The tensile force applied to the release plate <NUM> causes the washer <NUM> to slide along the slip surface <NUM> of the release plate and the fastener shank <NUM> to pull through the slot <NUM> and eventually release the release plate <NUM> from the frame <NUM> (see <FIG>), thereby allowing the hinge plate <NUM> to bend/deform and function as a living hinge. At the same time, the portion of the weld <NUM> between the gusset plate <NUM> and second flange <NUM> may tear, again allowing the hinge plate <NUM> to bend and deform. <FIG> shows the frame members at the end of the crash event, where the hinge plates <NUM>, defining living hinges, in the hinge assemblies permit continued rotation of rear and front frames <NUM>, <NUM> relative to the end frames <NUM>. As the hinge plates <NUM> bend along a preferred vertical axis, the release plates <NUM> slide and bend, thereby releasing from the grip of the bolts and backing washers. The release of the release plates is allowed due to the slot <NUM> in the release plate widening just enough for the release plate to bend away from and release the fastener <NUM>.

In the pre-impact configuration, which may constitute the entire life of the TMA, the side frames <NUM>, <NUM> are held in static location without relative motion between the components of the TMA. The release plates <NUM>, <NUM> function as part of the holding strength within the arms of the TMA. The release plates <NUM>, <NUM> maintain their original shape, and the static angle throughout the frame and structure of the TMA.

As a highway safety device, the TMA functions as an energy absorbing crash attenuator. When this occurs, the TMA absorbs the energy of an impacting vehicle during an impact event. As the impacting vehicle <NUM> is brought to rest, the energy is absorbed through the compression of energy absorbing cartridges, the motion of the frame, and the bending of the frame arms <NUM>, <NUM> as they collapse towards the support/host vehicle <NUM>.

During arm folding, the hinge plates <NUM>, <NUM> will bend as a hinge between the arm tube and the mating rigid assembly (mid-frame/central member or end frame member). As the arms <NUM>, <NUM> bend, the arms swing outward and do so by bending the hinge plates <NUM>, <NUM> as shown in <FIG> and <FIG>. As the hinge plates <NUM>, <NUM> bend along a preferred vertical axis, the release plates <NUM>, <NUM> slide and bend, releasing from the grip of the bolts and backing washers. The release is allowed due to the slot in the release plate widening just enough for the release plate to bend away from the bolt. Once the release plate has been fully released from the bolts and backing washers, the arms <NUM>, <NUM> are free to rotate through the bending axis of the hinge plates <NUM>, <NUM>.

Claim 1:
A crash attenuator (<NUM>, <NUM>) comprising:
a frame comprising a first frame member (<NUM>, <NUM>) having opposite first and second sides and a second frame member (<NUM>-<NUM>, <NUM>) having opposite first and second sides moveable relative to the first frame member (<NUM>, <NUM>) between a pre-impact configuration and an impact configuration, wherein the first (<NUM>, <NUM>) and second (<NUM>-<NUM>, <NUM>) frame members are rigidly connected with a hinge assembly (<NUM>, <NUM>) in the pre-impact configuration and wherein the first (<NUM>, <NUM>) and second (<NUM>-<NUM>, <NUM>) frame members are hingedly connected with the hinge assembly (<NUM>, <NUM>) in the impact configuration, characterised in that the hinge assembly (<NUM>, <NUM>) comprises:
a release plate (<NUM>, <NUM>) fixedly connected to the first side of the first frame member (<NUM>, <NUM>), wherein the release plate (<NUM>, <NUM>) comprises a fastener opening (<NUM>) and a slot (<NUM>) extending between the fastener opening (<NUM>) and an edge (<NUM>) of the release plate (<NUM>, <NUM>);
a hinge plate (<NUM>, <NUM>) spaced apart from the release plate (<NUM>, <NUM>), wherein the hinge plate (<NUM>, <NUM>) is fixedly connected to the second side of the first frame member (<NUM>, <NUM>) and is fixedly connected to the second side of the second frame member (<NUM>-<NUM>, <NUM>); and
a fastener (<NUM>) extending through the fastener opening (<NUM>) and connecting the release plate (<NUM>, <NUM>) to the second frame member (<NUM>-<NUM>, <NUM>) at a location spaced apart from and free of any engagement with the hinge plate (<NUM>, <NUM>) when the first (<NUM>, <NUM>) and second (<NUM>-<NUM>, <NUM>) frame members are in the pre-impact configuration, wherein the fastener (<NUM>) is releasable through the slot (<NUM>) as the first (<NUM>, <NUM>) and second (<NUM>-<NUM>, <NUM>) frame members are moveable from the pre-impact configuration to the impact configuration.