U.S. patent application number 10/290080 was filed with the patent office on 2003-11-20 for highway crash cushion.
Invention is credited to Cobb, Lincoln C., Leonhardt, Patrick A., Machado, John V..
Application Number | 20030215285 10/290080 |
Document ID | / |
Family ID | 22712081 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030215285 |
Kind Code |
A1 |
Leonhardt, Patrick A. ; et
al. |
November 20, 2003 |
Highway crash cushion
Abstract
A highway crash cushion provides a novel system response profile
that reduces the stopping distance of an impact event. This crash
cushion includes a frame that forms at least two bays arranged one
behind another in an anticipated impact direction. The frame
includes at least three transverse frames and side frames extending
between adjacent transverse frames. Each of the side frames is
outwardly bowed and includes first and second side frame elements
coupled to the respective transverse frames, and a hinge coupled
between the first and second side frame elements. At least one
energy absorbing element is disposed in one of the bays, and at
least first and second restraints are coupled to the side frames to
resist movement of the hinges at an early stage in an impact event.
The crash cushion is partially collapsed automatically as the crash
cushion is raised from a horizontal to a vertical position, and
then extended automatically to its operational position as the
crash cushion is lowered from the vertical to the horizontal
position. The energy absorbing elements can include tapered
frusto-conical sheet metal elements that are stacked with the
smaller ends facing first and second opposed sides of the energy
absorbing element.
Inventors: |
Leonhardt, Patrick A.; (Yuba
City, CA) ; Cobb, Lincoln C.; (Auburn, CA) ;
Machado, John V.; (Antelope, CA) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60611
US
|
Family ID: |
22712081 |
Appl. No.: |
10/290080 |
Filed: |
November 7, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10290080 |
Nov 7, 2002 |
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09561477 |
Apr 28, 2000 |
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6481920 |
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09561477 |
Apr 28, 2000 |
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09193046 |
Nov 16, 1998 |
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6092959 |
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Current U.S.
Class: |
404/6 |
Current CPC
Class: |
B60R 19/00 20130101;
B60R 2019/005 20130101; E01F 15/148 20130101 |
Class at
Publication: |
404/6 |
International
Class: |
E01F 013/00 |
Claims
1. A highway crash cushion comprising: a frame forming at least
first and second bays arranged one behind another in an anticipated
impact direction, said frame comprising: at least first, second and
third transverse frames spaced from one another along the
anticipated impact direction such that the first bay is between the
first and second transverse frames and the second bay is between
the second and third transverse frames; at least first, second,
third and fourth side elements, said first and second side elements
extending between the first and second transverse frames on
respective sides of the first bay, and said third and fourth side
elements extending between the second-and third transverse frames
on respective sides of the second bay; at least one energy
absorbing element disposed in at least one of the bays; in an
initial condition each of said side elements bowing outwardly from
the respective bay; in a collapsed condition after an impact of
sufficient seventy, at least some of the side elements bowing
outwardly to a greater extent than in the initial condition to
accommodate movement of the respective transverse frames toward one
another.
2. The invention of claim 1 wherein the first-mentioned energy
absorbing element is disposed in the first bay, and further
comprising a second energy absorbing element disposed in the second
bay, wherein the first and second energy absorbing elements are
shorter than the respective bays by respective first and second
distances in the anticipated impact direction, and wherein the
first and second distances differ from one another.
3. The invention of claim 1 wherein the first-mentioned energy
absorbing element is disposed in the first bay, and further
comprising a second energy absorbing element disposed in the second
bay, wherein the first and second energy absorbing elements differ
in stiffness in the anticipated impact direction.
4. The invention of claim 1 wherein the side elements and the
transverse frames are joined together to form a unit adapted to be
cantilevered from a vehicle.
5. A highway crash cushion comprising: a frame forming at least
first and second bays arranged one behind another in an anticipated
impact direction, said frame comprising: at least first, second and
third transverse elements spaced from one another along the
anticipated impact direction such that the first bay is between the
first and second transverse elements and the second bay is between
the second and third transverse elements; at least first, second,
third and fourth side elements, said first and second side elements
extending between the first and second transverse elements on
respective sides of the first bay, and said third and fourth side
elements extending between the second and third transverse elements
on respective sides of the second bay; at least one energy
absorbing element disposed in at least one of the bays; and in an
initial condition at least some of the side elements bowing away
from a respective line extending between end portions of the
respective side element.
6. A highway crash cushion comprising: a frame forming at least
first and second bays arranged one behind another in an anticipated
impact direction, each of said bays comprising a front and a back,
said frame comprising: at least first, second, third and fourth
side elements, each of said side elements extending between the
front and the back of a respective bay, said first and second side
elements disposed on respective sides of the first bay, and said
third and fourth side elements disposed on respective sides of the
second bay; at least one energy absorbing element disposed in at
least one of the bays; and in an initial condition at least some of
the side elements bowing away from a respective line extending
between end portions of the respective side element.
7. The invention of claim 5 or 6 wherein said at least some of the
side elements bow away from the respective lines to a greater
extent after an impact of sufficient severity than in the initial
condition, thereby accommodating compression of the at least one
energy absorbing element.
8. The invention of claim 5 wherein the side elements and the
transverse elements are joined together to form a unit adapted to
be cantilevered from a vehicle.
9. The invention of claim 5 or 6 wherein each of the side elements
bows outwardly from the respective bay in the initial
condition.
10. The invention of claim 5 or 6 wherein the first-mentioned
energy absorbing element is disposed in the first bay, and further
comprising a second energy absorbing element disposed in the second
bay, wherein the first and second energy absorbing elements are
shorter than the respective bays by respective first and second
distances in the anticipated impact direction, and wherein the
first and second distances differ from one another.
11. The invention of claim 5 or 6 wherein the first-mentioned
energy absorbing element is disposed in the first bay, and further
comprising a second energy absorbing element disposed in the second
bay, wherein the first and second energy absorbing elements differ
in stiffness in the anticipated impact direction.
Description
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 09/193,046, filed Nov. 16, 1988, which is
hereby incorporated by reference in its entirety.
BACKGROUND
[0002] The present invention relates to an improved highway crash
cushion that operates to decelerate an impacting vehicle safely and
efficiently.
[0003] Highway crash cushions are widely used to decelerate
impacting vehicles while limiting deceleration to safe levels for
occupants of the vehicles. Such cushions are used alongside
roadways in many applications, such as in front of bridge piers and
other obstructions. Additionally, highway crash cushions are
positioned on shadow vehicles such as heavy trucks that are parked
in front of work zones. The truck protects the work zone against
intrusion from a vehicle that has left the roadway, and the highway
crash cushion protects the impacting vehicle and the shadow truck
during the collision.
[0004] June U.S. Pat. No. 5,642,794, assigned to the assignee of
the present invention, discloses one highway crash cushion that is
mounted to a truck via a support frame that includes articulated
arms. An energy absorbing element is disposed in the support frame,
which is designed to collapse and to decelerate an impacting
vehicle in a controlled manner.
SUMMARY
[0005] The present invention is directed to an improved highway
crash cushion and associated method that provide important
advantages in terms of improved design flexibility. This allows the
crash cushion designer to tailor the decelerating loads imposed by
the crash cushion on the impacting vehicle to optimize efficiency.
This invention is defined by the following claims, and nothing in
this section should be taken as a limitation on those claims.
[0006] By way of introduction, the crash cushion described below
includes a frame that forms at least first and second bays arranged
one behind the other in an anticipated impact direction. The frame
includes at least first, second and third transverse frames spaced
from one another along the anticipated impact direction such that
the first bay is between the first and second transverse frames and
the second bay is between the second and third transverse frames.
At least four side frames are included in the frame, with the first
and second side frames extending between the first and second
transverse frames on respective sides of the first bay, and the
third and fourth side frames extending between the second and third
transverse frames on respective sides of the second bay. Each of
the side frames is outwardly bowed and includes first and second
side frame elements that are coupled to the respective transverse
frames, and a hinge coupled between the first and second side frame
elements. At least one energy absorbing element is disposed in at
least one of the bays, and at least two restraints are coupled to
the side frames to resist movement of the hinges.
[0007] The energy absorbing elements can take many forms. In one
preferred form the energy absorbing element includes tapered
deformable sheet metal elements. Each sheet metal element defines a
longitudinal axis extending between a smaller and a larger end, and
the longitudinal axes are generally aligned with some of the
smaller ends facing a first side of the energy absorbing element
and others of the smaller ends facing a second side of the energy
absorbing element, opposite the first side.
[0008] The crash cushion described in detail below is one example
of a new type of crash cushion having a system response profile
that provides an unusually efficient operation and stops an
impacting vehicle in an unusually short distance while complying
with controlling regulations. The system response profile of the
disclosed crash cushion is characterized by an initial portion, an
intermediate portion and a final portion. The decelerating force of
the response profile during the final portion has an average value
F; the decelerating force during the initial portion peaks at a
value substantially greater than F; and the decelerating force
during the intermediate portion falls to a value substantially less
than F. This system response profile initially slows the vehicle
markedly, then substantially reduces or eliminates decelerating
forces on the vehicle, and finally provides a controlled
decelerating force to stop the vehicle. In this way, the time and
distance required initially to slow the impacting vehicle by a
specified amount (such as 12 meters per second) is minimized, and
the impacting vehicle quickly reaches the third portion of the
profile, where the impacting vehicle is decelerated at a high
average rate, up to about 20 G in many applications.
[0009] The drawings and detailed description disclose the preferred
embodiments in greater detail, along with many of their
advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a perspective view of a first preferred embodiment
of the highway crash cushion of this invention.
[0011] FIG. 2 is a more detailed perspective view of the crash
cushion of FIG. 1.
[0012] FIGS. 3, 4 and 5 are front, top and side views,
respectively, of the crash cushion of FIG. 2.
[0013] FIG. 6 is a detailed view of a hinge and restraint included
in the embodiment of FIG. 2.
[0014] FIG. 7 is a top view of a second preferred embodiment of
this invention, showing the frame at an initial stage of collapse
during an impact.
[0015] FIGS. 8 and 9 are top views of the embodiment of FIG. 7,
showing the crash cushion in a partially collapsed position (FIG.
8) and an extended position (FIG. 9).
[0016] FIGS. 10 and 11 are side views of the embodiment of FIG. 7,
showing the crash cushion in an operational, horizontal position
(FIG. 10) and a vertical, transport/storage position (FIG. 11).
[0017] FIG. 12 is a graph of deceleration force versus time for two
variants of the embodiment of FIG. 2 during comparable impact
events.
[0018] FIG. 13 is an exploded perspective view of a portion of one
energy absorbing element suitable for use with this invention.
[0019] FIGS. 14 and 15 are a perspective, partially exploded view
and a front view, respectively, of deformable sheet metal elements
suitable for use in another energy absorbing element of this
invention.
[0020] FIGS. 16 and 17 are upper and lower perspective views of a
one-directional array of tapered deformable elements.
[0021] FIG. 18 is a perspective view of a bi-directional array of
tapered deformable elements.
[0022] FIG. 19 is a perspective view of a polygonal tapered
deformable element.
[0023] FIGS. 20 and 21 are perspective views of uni-directional and
bi-directional arrays, respectively, using the polygonal deformable
element of FIG. 19.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0024] Turning now to the drawings, FIG. 1 shows a crash cushion 10
that incorporates a presently preferred embodiment of this
invention. The crash cushion 10 is mounted at the rear of a shadow
vehicle or truck T by means of a mounting structure 18. The crash
cushion 10 includes a frame 12 described in greater detail below.
The frame 12 supports an impact face 14 directed away from the
truck T, and the frame 12 defines two bays that support respective
energy absorbing elements 16. The frame 12 forms a self-supporting
structure, and the energy absorbing elements 16 are designed to
absorb energy in an impact but not to serve a structural function
in the crash cushion 10.
[0025] FIG. 2 shows a more detailed perspective view of the crash
cushion 10, including transverse frames 20, 22 and 24 and side
frames 26, 27, 28, 30. The impact face 14 of FIG. 1 is not shown in
FIG. 2 for clarity of illustration, but the face 14 is mounted on
the transverse frame 20. In some embodiments, the face 14 can be
non-structural or even eliminated.
[0026] As best shown in FIG. 4, each of the side frames 26, 27, 28,
30 includes two separate side frame elements 32 that are
interconnected by a pair of central hinges 34. Additionally, each
of the side frame elements 32 is connected by additional hinges 36
to a respective one of the transverse frames 20, 22, 24. As shown
in FIG. 4, the side frame elements 32 are bowed outwardly, and the
hinges 34 are positioned to allow the side frame elements 32 to
move outwardly in an impact.
[0027] The transverse frames 20, 22 and the side frames 26, 27 form
a first bay 38 that contains the first element 16. Similarly, the
transverse frames 22, 24 and the side frames 28, 30 form a second
bay 40 that contains the second element 16. The energy absorbing
elements 16 are attached to and cantilevered from respective
transverse frames 22, 24.
[0028] As shown in FIG. 5, one or more hydraulic cylinders 52 can
be provided in the mounting structure 18 to pivot the frame 12
between the horizontal, operational position shown in FIGS. 5 and
10, and the vertical, storage/transport position shown in FIG. 11.
Cross braces 44 are mounted between the transverse frames as shown
in FIGS. 4 and 5 to provide stability prior to impact. These cross
braces 44 have been left out of the remaining figures for clarity
of illustration.
[0029] FIG. 6 provides an exploded perspective view of one of the
hinges 34 and the associated side frame elements 32. The hinge 34
is shown in a rotated position for clarity of illustration.
Normally the hinges 34 are oriented with vertical hinge axes, as
shown in FIGS. 2 and 4.
[0030] As shown in FIG. 6, a restraint 46 is associated with each
of the hinges 34. In this embodiment, the restraint 46 takes the
form of a bolt 48 and a nut 50. The bolt 48 is passed through
openings in mounting blocks 52, and the mounting blocks are rigidly
secured in place on respective ones of the side frame elements 32.
The hinge 34 in this embodiment is formed by a pin 56 that is
received within openings 54, 55. The opening 55 may be formed by a
sleeve 57 received in one of the hinge parts.
[0031] When the crash cushion 10 is in the operational position
shown in FIGS. 1 through 5, each of the eight hinges 34 is held in
the closed position by the respective restraint 46. Note that the
hinges 34 are positioned in such a way that compressive forces
applied to the frame 12 by an impacting vehicle (not shown)
striking the transverse frame 20 along the impact direction I (FIG.
4) apply tensile forces to the respective restraints 46. When these
tensile forces exceed the strength of the respective bolts 48 (FIG.
6), the bolts are broken, thereby freeing the hinges 34 to open
outwardly, and allowing the transverse frames 20, 22, 24 to
approach one another and to compress the energy absorbing elements
16.
[0032] FIGS. 7 through 11 relate to a second preferred crash
cushion, which is in many ways similar to the first crash cushion
described above. Comparable elements are given comparable reference
numbers. The crash cushion of FIGS. 7 through 11 differs from the
crash cushion 10 described above in that the side frame elements 32
secured to the first transverse frame 20 are additionally provided
with auxiliary hinges 58. As shown in FIG. 7, during a normal
impact the hinges 58 remain closed and the embodiment of FIGS. 7
through 11 operates quite similarly to the embodiment described
above in conjunction with FIGS. 1 through 6.
[0033] As shown in FIGS. 8 and 9, this embodiment also includes
cables 60 and 62. The cables 60 are connected to respective ones of
the forward side frame elements 32 adjacent to the auxiliary hinges
58. When the cables 60 are tightened and the cable 62 is loosened,
forces are applied to the forward side frame elements 32 to close
the auxiliary hinges 58 and to extend the first transverse frame 20
away from the second transverse frame to the operational position
shown in FIG. 9. Conversely, when the cables 60 are loosened and
the cable 62 is tightened, the first transverse frame 20 is pulled
toward the second transverse frame 22 as the auxiliary hinges are
opened, as shown in FIG. 8. In this way the overall length of the
crash cushion is reduced. The hinges 58 may be spring biased toward
the opening direction to facilitate this movement.
[0034] Preferably, the cables 60, 62 are attached to a mounting
structure similar to that discussed above in such a way that the
cables 60, 62 are loosened and tightened as described above
automatically as the crash cushion is rotated between the
horizontal, operational position of FIG. 10 and the vertical,
travel/storage position of FIG. 11. Thus, when the crash cushion is
raised to the vertical position of FIG. 11, the cables 60 are
automatically loosened and the cable 62 is automatically tightened
to shorten the travel height of the crash cushion automatically.
Conversely, as the crash cushion is lowered to the operational
position shown in FIG. 10, the cables 60 are automatically
tightened and the cable 62 is automatically loosened to extend the
first transverse frame 20 to the operational position shown in FIG.
9. In this way, the overall height of the crash cushion 10 in the
travel position can be maintained at the desired level, such as no
more than about 13 feet above the roadway.
[0035] The cables 60, 62 and the auxiliary hinges 58 function as a
means for automatically collapsing the first bay as the crash
cushion is rotated from the horizontal to the vertical position,
and as a means for automatically extending the first bay as the
crash cushion is rotated from the vertical to the horizontal
position. These elements also function as a means for at least
partially collapsing the frame 12 to shorten its length for
storage.
[0036] The means for automatically extending and retracting the
frame 12 can take many other forms. For example, the means for
extending the frame may include a spring-biased system that causes
the first bay of the frame 12 to remain fully extended when the
retraction cables are loosened. If desired, one or more latches can
be provided so that in the travel position and/or the operational
position the configuration of the crash cushion 10 is maintained by
some means other than tension on the cables.
[0037] FIG. 13 shows a preferred structure for one of the energy
absorbing elements 16. As shown in FIG. 13, a plurality of sheet
metal rectangular cells 90 are disposed between cover plates 92. In
an impact, these sheet metal elements are crushed to provide a
controlled decelerating force. The cells 90 and the cover plates 92
of FIG. 13 are similar to corresponding elements of U.S. Pat. Nos.
4,711,481 and 5,199,755, assigned to the assignee of the present
invention and hereby incorporated by reference in their
entirety.
[0038] Another preferred structure for the energy absorbing element
of FIG. 1 includes a plurality of tapered deformable elements.
Tapered deformable elements can take many forms, and several
examples are shown in FIGS. 14-21. In general, the tapered
deformable elements can be formed as separate, stand-alone tapered
elements that are stabilized by fastening both ends of the tapered
elements to a frame of some type, such as for example by use of
rivets, welds, adhesives or other fasteners. Alternately, the
tapered deformable elements can be formed in one or two dimensional
arrays.
[0039] FIGS. 14 and 15 relate to a first type of tapered deformable
element 94 in which the elements are generally conical in shape and
each includes a small end 98 and a large end 100 spaced along a
longitudinal axis 96. As shown in FIG. 14, in this embodiment the
tapered deformable elements 94 are closely stacked with some of the
small ends 100 oriented toward a first side 102 of the array, and
others of the small ends 98 facing the second, opposed side 104 of
the array.
[0040] In the end view of FIG. 15, the deformable elements are
identified as 94' and 94". The elements 94' have their small ends
98' facing the view plane, while the elements 94" have their small
ends 98" facing away from the view plane.
[0041] Returning to FIG. 14, in this embodiment the deformable
elements 94 are formed from two stamped sheets 106, 108 of a sheet
material such as sheet aluminum. Depending upon the desired
stiffness of the deformable elements, any appropriate gauge and
alloy of material can be used. As shown in the uppermost row of
FIG. 14, each of the sheets 106, 108 is stamped or otherwise formed
to create an array of half cones. The sheets 106, 108 may be
physically identical if the half cones are positioned properly on
the sheets. When the sheets 106, 108 are mated together, the
frustoconical shapes of the individual tapered elements 94 are
formed, as shown in the lower two rows of FIG. 14. The sheets 106,
108 can be held together in any suitable manner, as by spot
welding, riveting, fastening, or adhesively holding them together
or to an external frame (not shown).
[0042] FIGS. 16-18 relate to another preferred embodiment, in which
the tapered deformable elements 111 are each formed from a single
sheet 110 of a sheet material such as sheet aluminum. In this case
the tapered deformable elements 111 are stamped or drawn from the
sheet 110 in a conventional stamping or drawing operation. Thus,
the single sheet 110 forms all of the associated tapered elements
111, along with the remaining planar portion of the backing
sheet.
[0043] As shown in FIGS. 16 and 17, a single sheet 110 of the
tapered deformable elements 111 can be used to form a
uni-directional array. Alternatively, as shown in FIG. 18, two of
the sheets 110 can be nested together to form a bidirectional
array, in which the smaller ends of the elements 111 of one sheet
face a first direction, while the smaller ends of the tapered
elements 111 of the second sheet face the reverse direction.
[0044] It is not essential in all embodiments that the tapered
deformable elements be circular in cross section. As shown in FIGS.
19-21, various polygonal cross sectional shapes can be used. The
tapered deformable element 116 of FIG. 19 has a rectangular cross
sectional shape. Other polygonal shapes including polygons with
more or fewer sides arranged as regular or irregular polygons can
be used. As shown in FIGS. 20-21, polygonal tapered deformable
elements 116 can be arranged in a uni-directional array 118 or a
bi-directional array 120.
[0045] Though not shown in FIGS. 14-21, conventional cover plates
can be used to house and secure the tapered deformable elements in
place, if desired, and multiple rows of the illustrated elements
can be used in a single energy absorbing element.
[0046] The tapered deformable elements provide the advantage of an
increased stroke and thereby increased efficiency. This is because
the tapered deformable elements 94, 111, 116 can be crushed to a
small fraction of their original length before metal-to-metal
contact of the crushed element provides substantial increases in
the forces required for further crushing
[0047] The crash cushion 10 reacts to the impact of a vehicle in
the following way. First the impacting vehicle contacts the rear
impact face 14. This face provides a uniform surface for the
vehicle to interact with and transfers the loading from the vehicle
to the crash cushion 10. The side frame elements 32 begin to flex
because of this loading and then continue to flex until the
restraints 46 fail. The amount of loading that is applied to an
impacting vehicle can be tuned by taking into account the several
factors that determine when the restraints release the respective
hinges. These factors may include the geometry of the hinges 34 and
the side frame elements 32 in relation to the location of the
restraints 46, the ultimate strength of the bolts 48, the stiffness
of the side frame elements, and the mass of the side frame
elements, the transverse frames and the face 14.
[0048] Once the restraints 46 fail, the side frame elements 32
begin to rotate in response to the force supplied by the impacting
vehicle to the transverse frame 20. The translation of transverse
frame 20 and the rotation of the side frame elements 32 cause a
transfer of kinetic energy that was originally in the impacting
vehicle into the frame 12, thereby slowing the impacting vehicle.
The side frame elements 32 continue to collapse until the gaps G1,
G2 between the energy absorbing elements 16 and the transverse
frames 20, 22 have closed (FIG. 4). The energy absorbing elements
16 are then deformed as they collapse until the design level of
kinetic energy has been dissipated by the system or the vehicle has
been brought to a stop.
[0049] The crash cushion 10 is designed so that under many impacts
most of the components of the frame 12 are reusable. The energy
absorbing elements 16 are expendable and are intended to be
replaced after an impact.
[0050] The initial decelerating forces applied by the crash cushion
10 to an impacting vehicle are determined as a function of (1) the
linear inertia of the component elements of the frame 12 (e.g. the
mass of the transverse frame 20), (2) the linear and rotational
inertia of the side frame elements 32, and (3) the angular offset
of each side frame element 32 with respect to the collapsing loads
applied during an impact. Note that both the linear and the
rotational inertial responses of the system do not involve any
planned deflection of, tearing of, or other damage to the frame
12.
[0051] The initial impact response of the crash cushion 10 also
depends on the use of mechanical or electromechanical restraints
that limit release of the collapsible bays until some desired
minimum threshold level of impact severity is achieved. The system
described above is completely passive, and relies on the breaking
of bolts placed in tension by the impact to control the release of
the frame 12. Other passive means such as shear pins, breakaway
cables, or high-friction brakes in each of the hinges 34 can also
be used. Alternatively, restraints suitable for use with this
invention may involve sensors and/or controls that adjust the
properties of the release to best suit the particular
characteristics of the impacting vehicle, after some determination
is made about the conditions of the impact. For example, a
restraint may include an electromechanical device. When a load (as
measured by an integral load cell) reaches a threshold value, a
locking pin may be pulled out of a joint by an actuator, thus
releasing the hinge. Thus, the restraints that limit collapse of
the frame may or may not be reusable and they may be passive or
active. The key characteristic is that the collapse of the system
is released under specific and predictable conditions, but not
otherwise. Active restraints may allow collapse of the frame to be
conditional on any desired combination of impact conditions such as
force, velocity, and displacement.
[0052] By adjusting the inertial properties of the transverse
frames 20, 22 and the side frame elements 32, by adjusting the
geometry of the side frame elements 32 (i.e. the amount the side
frame elements 32 are bent at their hinges 34 in their deployed,
operational position), and by adjusting the characteristics of the
restraints 46, the response of the crash cushion 10 can be tailored
to optimally trigger onboard airbags or other onboard safety
systems of an impacting vehicle. One particular challenge for
airbags is the distinguishing of conditions requiring deployment of
the airbag, for example a high-speed accident, from conditions
under which the airbag is not required, for example a low speed
bump into a parking bollard or another vehicle. By adjusting the
response of the crash cushion, the problem of non-deployment, or
inappropriate deployment of airbags can be reduced. For example, by
adjusting crash cushion parameters to obtain a relatively high
initial deceleration spike, the crash cushion 10 can provide an
initial force on the impacting vehicle that is large enough and
shaped to tend to ensure the deployment of an airbag early in the
impact, thus maximizing the benefit of the airbag to the vehicle
occupants.
[0053] The crash cushion 10 can also be designed to reduce the
overall length of the crash cushion 10. It is generally true that
the greater the length of a crash cushion, the lower the forces of
impact will be. However, additional length limits the sites at
which a particular crash cushion may be properly applied. In the
application of a crash cushion mounted to the back of a truck, the
length of the crash cushion is of particular sensitivity, in that
additional length adds weight that must be supported by the frame
of the truck. Further, the weight of the truck-mounted crash
cushion is generally cantilever-mounted to the truck, so that
additional length increases the moment of the weight of the crash
cushion on the mounting structure 18. Also, as the length of a
truck-mounted crash cushion increases, the rearmost end of the
crash cushion will tend to swing widely as the truck turns. For
these reasons, reducing the length of truck-mounted crash cushions
is of particular benefit.
[0054] As the length of a crash cushion is reduced, it is important
that the impact response of the crash cushion is very carefully
designed so to continue to provide optimal safety performance. The
ability of the designer to tune the response of the crash cushion
allows this delicate balance between the system's length and its
impact performance to be established.
[0055] Another advantage of the frame 12 is that it can be
collapsed to a very compact size for shipping and storage. If the
included energy absorbing elements 16 are themselves collapsible
(e.g. formed of hydraulic or pneumatic elements), then the frame 12
can be collapsed while mounted on the truck T so that the crash
cushion 10 can be made very compact when the truck T is in
transit.
[0056] Actual crash tests have shown that the crash cushion 10 can
readily be tuned by adjusting the parameters described above to
obtain a desired deceleration curve. FIG. 12 shows two curves 80,
82 of decelerating force versus time as an impacting vehicle
strikes the crash cushion 10. The principal differences between the
tests that resulted in the curves 80 and 82 relate to selected ones
of the variables described above. For the curve 80, two energy
absorbing elements 16 were used, but the energy absorbing element
16 in the first bay was shorter and less stiff than the energy
absorbing element in the second bay. In particular, the gap G1 was
33 inches while the gap G2 was seven inches. The conditions used
for the curve 82 included no energy absorbing element in the first
bay and a gap of only one inch between the energy absorbing element
of the second bay and the second transverse frame 22. Note that the
curve 80 provides a second peak after the initial spike that occurs
substantially earlier during the crash than the second peak in the
curve 82. The magnitudes and locations in time of the peaks can be
controlled by properly choosing the system parameters discussed
above.
[0057] From the foregoing it should be apparent that an improved
highway crash cushion has been described that lends itself to being
tuned by the designer for particular impact characteristics. For
the crash cushion 10, there are at least five variables that can be
selected for each of the two bays: linear inertia, rotational
inertia, stiffness of the energy absorbing element in the bay, gap
between the energy absorbing element and the respective transverse
frames, and release load of the restraints. Any of these variables
can be set at different levels for the two bays. Furthermore, the
two bays cooperate with one another in a complex way.
[0058] The preferred crash cushion of this invention arranges these
variables to achieve a novel system response profile that meets
currently-prevailing regulatory standards while providing a
dramatically shortened crash cushion.
[0059] Impact testing of crash cushions is guided in North America
by the National Cooperative Highway Research Program Report 350
(NCHRP-350). The NCHRP-350 guidelines rely on the flail space model
for evaluation of occupant risk during an impact test. The flail
space model assumes an unrestrained occupant in the front seat of
the vehicle. At the beginning of the crash event, the vehicle is
decelerated by the impact with the crash cushion, while the
occupant continues forward in an unimpeded manner. At some point,
the occupant makes contact with the inside of the vehicle, and the
NCHRP-350 guidelines specify limits on the velocity of the occupant
relative to the vehicle at the moment of contact. Once the occupant
has come into contact with the vehicle interior, he or she is
assumed to remain in contact with the vehicle as it is decelerated
to a stop. The NCHRP-350 guidelines specify that while the occupant
is in contact with the vehicle interior, the magnitude of
deceleration of the vehicle must not exceed 20 G. These guidelines
also specify that the occupant shall not come into contact with the
vehicle at a relative speed greater than 12 meters per second.
[0060] For the purposes of this discussion, the portion of an
impact event or crash up to the instant of occupant impact with the
interior of the vehicle will be referred to as the delta-V segment
or portion, and the remainder of the event (from occupant impact
until the vehicle comes to rest) will be referred to as the
ride-down segment.
[0061] The delta-V segment and the ride-down segment for one impact
are shown in FIG. 12. The delta-V segment is divided into an
initial portion and an intermediate portion, and the ride-down
segment corresponds to the final portion of the impact event. These
legends are relevant only to the curve 80. The curve 82 has been
tuned for other characteristics and is not relevant in this
discussion.
[0062] As shown in FIG. 12, the initial portion of the system
response profile is characterized by a high peak deceleration, that
is associated with a peak decelerating force exceeding 3F in this
embodiment. The initial portion is followed by an intermediate
portion in which vehicle deceleration falls. The intermediate
portion is characterized by a substantial reduction in decelerating
forces on the vehicle. In this case, the decelerating forces
approximately reach zero.
[0063] Once the vehicle has been decelerated by the desired
velocity (such as 12 meters per second), the crash cushion then
provides a controlled deceleration below the regulatory limit of 20
G during the final portion. In the final portion the average
decelerating force is at the level F shown in FIG. 12.
[0064] The curve 80 is provided by way of example. In general, it
is preferred to apply high decelerating forces to the impacting
vehicle that peak at F1 during the initial portion of the impact
event. F1 is preferably at least about 150% of F, more preferably
at least about 200% of F, and most preferably at least about 300%
of F. This provides a sharp deceleration to the vehicle which
contributes to a short stopping distance for the impact event.
However, if the high peak deceleration of the initial portion of
the impacting event were continued, the vehicle would be
decelerated to such an extent that the occupant would strike the
interior of the vehicle with an excessively high velocity. In order
to prevent this undesired result, the intermediate portion of the
impact event or the response profile falls to a decelerating force
that is substantially less than F. Preferably, the decelerating
force falls to a value F2 that is less than 50% of F, more
preferably less than 20% of F, and most preferably less than 10% of
F. The decelerating force preferably remains below this value for
at least 20 mS, more preferably at least 30 mS, and most preferably
at least 40 mS. The foregoing values are provided for force levels
and time durations as independent parameters, and are not intended
to indicate a preference for any specific combination of force
level and time duration.
[0065] The inventors of the present invention have discovered that
by taking the counterintuitive step of substantially reducing
decelerating forces on the vehicle during the intermediate portion
of the impact event, following the sharp peak in decelerating
forces during the initial portion, the total elapsed time and the
total elapsed distance of the impact event can be reduced. Because
a short impact event is important for many applications, this
represents a significant advance in the art.
[0066] Simply by way of example, significant system parameters
associated with the system that produced the deceleration curve 80
of FIG. 12 are described in Table I.
1TABLE I Preferred Crash Cushion Parameters A. Mass of Frame
Elements transverse frame 20 129 kg transverse frame 22 58 kg side
frame element 32 32 kg B. Moment of Inertia side frame element 32
1.92 kg-m.sup.2 C. Bolts 48 Hex bolt, 3/8", coarse thread, grade 8
D. Gaps G1 = .229 m G2 = .178 m E. Front Energy Absorbing Element
16 Number of cells per row Material thickness (mm) Row 1 (Front) 4
.81 Row 2 4 .81 Row 3 8 .81/1.02 (4 cells of each) Row 4 8 .81/1.02
(4 cells of each) Row 5 (Rear) 8 1.02 F. Rear Energy Absorbing
Element 16 Number of cells per row Material thickness (mm) Row 1
(Front) 8 .81 Row 2 12 1.27 Row 3 12 1.27 Row 4 12 1.27 Row 5
(Rear) 12 .81/1.02 (6 cells of each)
[0067] In the crash cushion of Table I, the energy absorbing
elements 16 each include five rows of sheet aluminum cells. FIG. 13
shows a twelve cell row, and the other rows were similar, but with
fewer cells per row where appropriate.
[0068] The crash cushions described above represent only one
approach to achieving the desired system response profile. Many
other approaches are possible. For example, a large inertial mass
can be placed at a selected distance in front of a conventional
crash cushion, such as the truck-mounted attenuator described in
U.S. Pat. No. 5,199,755. Alternately, a brake-based crash cushion
such as that described in U.S. Pat. No. 5,022,782 can be provided
with an intermediate portion of the stroke in which the braking
efficiency, and thereby the decelerating force, are substantially
reduced. This can be done by properly adjusting the dimension,
material or lubrication of the brake cable. As yet another example,
the high peak deceleration during the initial portion of the impact
event can be provided by a pneumatic or hydraulic energy absorbing
system that is followed after a specified gap by a second, less
stiff energy absorbing system.
[0069] In a further example of such a system provided with a
pneumatic or hydraulic energy absorbing system, the energy
absorbing means can be valved to provide an initial force peak,
followed by a dramatic reduction in resistive force, then finally
followed by a second, lower resistive force. More specifically, the
initial peak force can be provided by a pre-pressurized pneumatic
element, for example a gas-containing bag, with the pneumatic
element allowed to rapidly vent immediately after that initial peak
force so that the resistive force of the crash cushion falls
dramatically during the intermediate segment of the crash event,
after which the gas-containing bag can be explosively
re-pressurized to provide the necessary resistive force during the
final segment of the crash event. Another approach is to use a
stiff crushable element to provide the ideal response profile. A
mechanical release, as disclosed by June U.S. Pat. No. 5,642,794
would then release after a specified amount of crush had taken
place.
[0070] Another approach to generating the desired system response
profile is to support the impact face of the crash cushion with a
sacrificial mechanical support that provides the needed initial
peak force but is then completely crushed or shattered so that its
resistance drops to near zero for the intermediate segment of the
crash event, after which the impacting vehicle engages a more
conventional crash element for the final segment of the crash
event. The crushable element can be replaced by elements that are
extruded, split, curled, kinked, or otherwise mechanically
deformed.
[0071] A suitable crash cushion can also be made with bays that
collapse via sliding elements instead of or in addition to some of
the hinged elements of the crash cushion 10.
[0072] In general, the widest variety of energy absorbing systems
can be used to provide the desired system response profile, and
different energy absorbing technologies can be used to achieve
different portions of the system response profile. The widest
possible range of material bending, material tearing, material
crushing, material shattering, friction, hydraulic, pneumatic, and
inertial systems can be used either alone or in various
combinations to achieve the response profile discussed above.
[0073] Of course, many changes and modifications can be made to the
preferred Embodiments described above. For example, the frame can
be made in whole or in part of solid panels as opposed to the
illustrated construction. Similarly, the transverse frames can
include solid panels and may differ from one another in thickness
and in mass. If desired, the folding sides of the frame may be
positioned at the top and the bottom of the crash cushion instead
of on the lateral sides. Living hinges can be substituted for the
multiple-component hinges illustrated, and as described above many
alternatives are available for the restraints. Any suitable energy
absorbing element technology can be adapted for use with this
invention, including hydraulic, pneumatic, material-deforming,
tearing, or pulverizing and other approaches. Both passive and
active systems may be employed. By "active" is meant systems in
which sensors provide information to the crash cushion which is in
some manner evaluated and used to alter the performance of the
crash cushion prior to and/or during the impact. Furthermore, it is
not essential that each energy absorbing element be confined to a
single bay. If desired, the transverse frames can define central
openings that allow a single energy absorbing element to occupy
space in two or more bays. This invention is not limited to use in
truck mounted attenuators, but can also be used in front of other
roadside obstructions, including fixed roadside obstructions such
as bridge piers for example. Also, more than two bays may be used
if desired.
[0074] As used herein the term "conical" is intended broadly to
include frusto-conical shapes and the term "storage" is intended
broadly to include transport as well as storage. The term "cable"
is intended broadly to cover tension members generally, including
chains, wire ropes, ropes, and the like.
[0075] The foregoing detailed description has described 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 by way of limitation. It is only the following claims,
including all equivalents, that are intended to define the scope of
this invention.
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