A vehicle impact attenuator includes an array of resilient, self-restoring tubes arranged along a longitudinal axis. This array includes two or more tubes per row. The tubes each include a respective compression element oriented at an acute angle with respect to the longitudinal axis of the array, and an elongated structure such as a set of cables or rails is positioned between the tubes and in alignment with the longitudinal axis. The tubes are guided for sliding movement along the rail or cables in an axial impact, and the tubes, compression elements, guides, and rail cooperate to redirect a laterally impacting vehicle.
SUMMARY
By way of introduction, the impact attenuators described below include a central, elongated structure that is designed to resist lateral deflection. Tubes are mounted on either side of this elongated structure to slide along the structure in an axial impact and to react against the structure and redirect the vehicle in a lateral impact. The tubes are formed of a resilient, self-restoring material such as an elastomer or a high-density, high-molecular-weight polyethylene. Compression elements are mounted in the cylinders, and these compression elements are oriented at an angle of about 60.degree. to the longitudinal axis of the array to improve the redirection capabilities of the system.
The foregoing paragraph has been provided by way of general introduction, and it should not be used to narrow the scope of the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an impact attenuator that incorporates a first preferred embodiment of this invention.
FIG. 2 is a perspective view of a pair of tubes and associated guide and compression elements of the system of FIG. 1.
FIGS. 3, 4, 4a, and 5 are perspective, enlarged elevation, perspective, and plan views, respectively, showing portions of one of the transverse elements of FIG. 1.
FIG. 6 is a perspective view of one of the tubes of FIG. 1, showing the internal compression element.
FIG. 7 is a perspective view of the compression element of FIG. 6;
FIG. 8 is a perspective view of portions of an alternative guide that allows sliding attachment between the guide and the adjacent tubes.
FIG. 9 is a top view of a second preferred embodiment of the impact attenuator of this invention.
FIGS. 10 and 11 are top views of a third preferred embodiment of the impact attenuator of this invention, before and after axial compression, respectively.
FIGS. 12 and 13 are top views of one of the cylinders of FIGS. 10 and 11 and the associated compression element, before and after axial compression, respectively.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
FIG. 1 shows an overall view of a vehicle impact attenuator 10 in an initial condition, prior to impact. The attenuator 10 is shown positioned forwardly of a backup 12, which can be any hazard alongside a roadway from which vehicles are to be protected. For example, the backup 12 can be a bridge pier, a wall, or other obstruction positioned alongside the roadway.
The attenuator 10 includes an array 14 of tubes 16. In this embodiment, all of the tubes 16 are cylindrical in shape, and they are oriented with their cylinder axes positioned vertically. The tubes 16 are preferably formed of a resilient, polymeric material, such as high density polyethylene (HDPE), such that the tubes 16 are self-restoring after an impact. As used herein, the term "self-restoring" signifies that the tubes return substantially (though not in all cases completely) to their original condition after at least some impacts. Thus, the tube does not have to return to exactly its original condition to be considered self-restoring.
The array 14 defines a longitudinal axis 18 extending forwardly from the backup 12, and the array 14 includes a front end 20 positioned farther from the backup than the back end 22.
As described in greater detail below, the tubes 16 are secured together and to the backup 12, and at least the majority of the array 14 includes rows of the tubes 16, each row having at least two tubes. In this example, each of the rows includes two adjacent tubes, each disposed on a respective side of the longitudinal axis 18. Each of these tubes includes a compression element 24 that is designed to resist compression of the respective tube 16 along a respective compression axis 26, while allowing elongation of the tube 16 along the same axis 26 and collapse of the tube along the longitudinal axis of the array.
In this embodiment, an elongated structure 28 takes the form of a rail 30 that is secured in place in alignment with the longitudinal axis 18, for example, by bolting the rail 30 to the support surface. This rail may take the form of the rail described in U.S. Pat. No. 5,733,062, assigned to the assignee of the present invention and hereby incorporated by reference. The attenuator 10 also includes a plurality of guides 32. In this embodiment, each of the guides 32 includes a transverse element 34 that is secured to adjacent ones of the tubes 16 and is configured to slide along the length of the rail 30, in an axial impact.
In an axial impact, the transverse elements 34 slide along the rail 30, and the tubes 16 are flattened along the longitudinal direction. Deformation of the tubes 16 absorbs kinetic energy and decelerates the impacting vehicle.
In a lateral impact, the compression elements 24 transfer compressive loads to the transverse elements 34, which in turn transfer these compressive loads to the rail 30. This provides substantial lateral stiffness to the attenuator
such that the attenuator 10 redirects an impacting vehicle that strikes the attenuator 10 laterally. Because the guides 32 and the elongated structure 28 are positioned centrally, a vehicle traveling down the side of the attenuator 10 encounters few snagging surfaces that might adversely affect the stability or trajectory of the impacting vehicle.
FIG. 2 provides a more detailed view of selected elements of the attenuator 10. Note that the transverse element 34 in this embodiment is shaped as a frame with substantial stiffness, and that it is provided with plates 38 shaped to fit under an uppermost flange of the rail 30 (FIG. 1) such that the transverse element 34 is restrained from all translation other than axial sliding movement along the length of the rail 30. Each transverse element includes two legs 40 that rest on the support surface on opposite sides of the rail. In the event of a lateral impact, the leg on the side of the rail opposite the impact cooperates with the plates 38 and the rail 30 to resist rotation and lifting of the transverse element 34. Preferably, the plates 38 are shaped to allow twisting of the transverse element 34 about a vertical axis over a desired range (e.g., .+-.25.degree.) to reduce binding with the rail 30.
FIGS. 3 and 4 show details of construction of the plates 38 and the rail 30. Note that the fit between the plates 38 and the rail 30 is loose, and this fit allows the desired degree of twisting of the transverse element without binding. The range of allowed twisting is preferably greater than .+-.10.degree., more preferably greater than .+-.20.degree., and most preferably about .+-.25.degree., all measured with respect to the longitudinal axis of the rail 30. The dimensions of Table 1 have been found suitable in one example, in which the plates 38 were shaped as shown in FIG. 4a, and the plates 38 extended 7.6 cm along the rail (including the chamfered corners).
TABLE 1
Parameter Dimension (cm)
A 0.47
B 1.59
C 1.11
FIG. 5 shows one of the transverse elements 34 twisted by 25.degree. with respect to the rail 30. Many alternatives are possible, including other shapes for the plates 38. For example, the plates 38 may present a curved bullet nose to the rail.
This approach can be used in vehicle impact attenuators of other types, e.g., the attenuator of U.S. Pat. No. 5,733,062, and a wide variety of energy absorbing elements can be used between the transverse elements, including sheet metal elements, foam elements, and composite elements of various types. See, e.g. the energy absorbing elements of U.S. Pat. Nos. 5,733,062, 5,875,875, 4,452,431, 4,635,981, 4,674,911, 4,711,481 and 4,352,484.
As shown in FIG. 2, the tubes 16 are each secured in two places to each adjacent transverse element 34, as for example by suitable fasteners such as bolts passing through the holes 37. Also as shown in FIG. 6, each of the compression elements 24 is secured at one end only to the respective tube 16, as for example by suitable fasteners such as bolts. Each compression element 24 extends substantially completely across the respective tube 16 in the initial condition (e.g., by more than about 80% of the tube diameter), and it is designed to resist compression while allowing extension of the tube 16 along the compression axis 26. As shown in FIG. 6, one end of each of the compression elements 24 is free of tension-resisting attachment to the respective tube 16.
FIG. 6 shows a perspective view of one of the tubes 16 and the associated compression element 24. The compression element 24 is shown in greater detail in FIG. 7. As shown in FIG. 7, the compression element 24 is shaped as a frame in this embodiment, and the compression element includes openings 25 that receive fasteners (not shown) that secure one end only of each compression element 24 to the respective tube 16.
Though FIG. 2 shows only two tubes 16 secured to the transverse element 34, when fully assembled there are a total of four tubes 16 secured to each of the transverse elements 34: two on one side of the rail 30, and two on the other. Thus, each tube 16 is bolted in place between two adjacent transverse elements 34. This arrangement is shown in FIG. 1.
In the event of an axial impact, the impacting vehicle first strikes the front end 20. The momentum of the impacting vehicle causes the transverse elements 34 to slide along the rail 30, thereby compressing the tubes 16 such that they become elongated transverse to the longitudinal axis and flattened along the longitudinal axis. In order to prevent any undesired binding, it is preferred that the tubes 16 within any given row be spaced from one another in an initial condition, e.g., by about one-half the diameter of tubes 16. After the impact, the system can be restored to its original configuration by pulling the forward transverse element 34 away from the backup 12. In many cases, nothing more is required by way of refurbishment.
In the event of a lateral impact at a glancing angle, e.g. 20.degree., the impacting vehicle will strike the side of the array 14. The compression elements 24 transfer compressive loading to the transverse elements 34, which transfer this compressive loading to the rail 30. In this way, the attenuator 10 provides substantial lateral stiffness and effective redirection of an impacting vehicle.
In the preferred embodiment described above, the orientation of the compression elements at approximately 60.degree. with respect to the longitudinal axis of the array has been found to provide advantages in terms of improved vehicle redirection. In this configuration, the outboard end of each compression element is positioned forwardly of the in board end of each compression element, at the illustrated angle with the longitudinal axis. Of course, other angles can be used.
In the embodiment of FIGS. 1-7, the array 10 may have a length of 9.1 meters, and each of the tubes may have a height of 102 cm and a diameter of 61 cm. The tubes 16 may be formed of Extra High Molecular Weight Polyethylene resin (e.g., EHMW PE 408 ASTM F714) with a wall thickness of 1.875 (for tubes 16 at the front of the array) and 2.903 cm (for tubes 16 at the rear of the array), all as specified by ASTM F714. All of these dimensions may be varied to suit the particular application.
Of course, many alternatives are possible to the preferred embodiment described above. FIG. 8 shows an alternative form of the transverse element 34. In this alternative, the transverse element 34 is provided with slots positioned to receive the fasteners that secure the tubes to the transverse element. The slots allow the tubes to move laterally outwardly as necessary during an axial impact to prevent any undesired binding between the tubes within a row at the centerline.
FIG. 9 relates to another alternative embodiment in which the elongated structure that provides lateral rigidity is implemented as a set of cables 44. These cables 44 are positioned to support a central portion of the tubes 16, and the tubes 16 are secured to the cables 44 by means of guides 45 that may take the form of eye-bolts or U-bolts. In this example, the compression elements 24 are positioned transversely to the longitudinal axis 18 and are secured to the guides 45. Load-sharing diaphragms 46 are provided to transfer lateral loads from one of the cables to the other. The cables are anchored rearwardly to the backup 12 and forwardly to ground anchors 46. If desired, extra redirecting cylinders 48 may be positioned between the tubes 16.
FIGS. 10 and 11 relate to a third embodiment that is similar to the embodiment of FIG. 9 in many ways. FIG. 10 shows the system prior to impact with a vehicle, and FIG. 11 shows the system following an axial impact. Note that the compression elements 24 are designed to resist collapse of the tubes 16 in the lateral direction, while allowing expansion of the tubes 16 in the lateral direction.
The embodiment of FIGS. 10 and 11 uses a modified compression element 24 that is telescoping and is secured at both ends to the tube 16. FIG. 12 shows the telescoping compression element in its initial condition, and FIG. 13 shows the telescoping compression element during an axial impact when the tube 16 is elongated. If desired a tension spring 50 can be provided to restore the distorted tube 16 to the initial condition of FIG. 12 after an impact. The telescoping compression element of these figures can be used in any of the embodiments described above.
Of course, many changes and modifications can be made to the preferred embodiments described above. For example, when the elongated structure is implemented as a rail, two or more rails can be used rather than the single rail described above. The tubes 16 can be formed of a wide variety of materials, and may be non-circular in cross section (e.g. rectangular, oval, or triangular). The compression elements can be shaped either as frames or struts, as described above, or alternately as panels or other shapes designed to resist compression effectively. In some cases, a single compression element can be placed within each tube. In other cases, multiple compression elements may be placed within each tube, for example at varying heights.
Similarly, the guides described above can take many forms, including guides adapted to slide along a cable as well as guides adapted to slide along one or more rails. The guides may or may not include transverse elements, and if so the transverse elements may be shaped differently than those described above. For example, rigid panels may be substituted for the disclosed frames.
As another alternative, a separate guide may be provided for each tube rather than having a single transverse element to which multiple tubes are mounted. Also, there may be a smaller ratio of guides to tubes such that some of the tubes are coupled only indirectly to one or more guides (e.g. via intermediate tubes). In this alternative, two or more tubes that are spaced along the longitudinal axis of the array may have no guide therebetween.
The angle of the compression axes, the number of transverse elements 34 per system, the number of tubes per system, the location of the compression elements within the tubes, and the number of compression elements per tube may all be varied as appropriate for the particular application. Also, it is not essential that every tube include a compression element or that every tube be directly connected to a guide, and selective use of compression elements and/or guides with only some of the tubes is contemplated.
As used herein, the term "tube" is intended broadly to encompass tubes of any desired cross-section. Thus, a tube does not have to be circular in cross-section as in the illustrated embodiment.
The term "set" is used in its conventional way to indicate one or more.
The term "compression element" is intended to encompass a wide variety of structures that effectively resist compressive loads along a compression axis while allowing substantial compression transverse to the compression axis.
The foregoing detailed description has discussed only a few of the many forms that this invention can take. For this reason, this detailed description is intended by way of illustration, and not limitation. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.
