U.S. patent application number 09/811712 was filed with the patent office on 2001-09-27 for damped crash attenuator.
Invention is credited to Breed, David S..
Application Number | 20010024043 09/811712 |
Document ID | / |
Family ID | 27370980 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024043 |
Kind Code |
A1 |
Breed, David S. |
September 27, 2001 |
Damped crash attenuator
Abstract
A crash attenuator for protecting a truck or stationary
structure from damage resulting from impact of an object such as a
vehicle including a frame mountable to a truck or stationary
structure, a bumper having an impact-receiving face adapted to
receive an impact from an object in a crash, a movable displacement
structure coupled to the frame and interposed between the frame and
the bumper and having a first position in which the bumper is
relatively distant from the frame and a second position in which
the bumper is relatively proximate to the frame, and an energy
dissipation system coupled to the displacement structure for
dissipating the impact energy of the object into the bumper which
causes the displacement structure to be moved from the first
position toward the second position.
Inventors: |
Breed, David S.; (Boonton
Township, NJ) |
Correspondence
Address: |
BRIAN ROFFE, ESQ
366 LONGACRE AVENUE
WOODMERE
NY
11598
|
Family ID: |
27370980 |
Appl. No.: |
09/811712 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09811712 |
Mar 19, 2001 |
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09200367 |
Nov 23, 1998 |
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6203079 |
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60066486 |
Nov 24, 1997 |
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Current U.S.
Class: |
293/119 |
Current CPC
Class: |
F16F 9/0472 20130101;
B60R 21/0134 20130101; B60R 19/00 20130101; B60R 2019/005 20130101;
E01F 9/662 20160201; B60R 21/0136 20130101; B60R 2019/007 20130101;
E01F 15/148 20130101; B60R 19/40 20130101; B60R 19/20 20130101;
F16F 7/121 20130101 |
Class at
Publication: |
293/119 |
International
Class: |
B60R 019/40 |
Claims
I claim:
1. A crash attenuator which receives an impact force from a moving
object and dissipates the impact energy of the object to thereby
reduce the velocity of the object comprising a frame mountable to a
truck or stationary structure, a bumper having an impact-receiving
face adapted to receive the impact from the object in a crash, a
movable displacement structure coupled to said frame and interposed
between said frame and said bumper and having a first position in
which said bumper is relatively distant from said frame and a
second position in which said bumper is relatively proximate to
said frame, and energy dissipation means coupled to said
displacement structure for dissipating at least some of the impact
energy of the object received by said bumper which causes said
displacement structure to be moved from the first position toward
the second position and thereby reducing the velocity of the
object, wherein said energy dissipation means are structured and
arranged to provide an energy dissipation force for dissipating the
impact energy of the object based on deceleration of the
object.
2. The crash attenuator of claim 1, wherein said displacement
structure is a collapsible structure composed of a plurality of
members arranged to provide said collapsible structure with a
contracted position corresponding to the second position of said
displacement structure and an expanded position corresponding to
the first position of the displacement structure.
3. The crash attenuator of claim 1, wherein said displacement
structure is movable back to the first position from the second
position such that the crash attenuator is reusable.
4. The crash attenuator of claim 1, wherein said energy dissipation
means are arranged to regulate movement of said displacement
structure from the first position toward the second position such
that the energy dissipation force for dissipating the impact energy
of the object is variable.
5. The crash attenuator of claim 1, further comprising deceleration
sensing means for continuously sensing the deceleration of the
object after impact into said bumper to determine an instantaneous
deceleration of the object and said energy dissipation means are
arranged to vary the energy dissipation force based on the
instantaneous deceleration of the object.
6. The crash attenuator of claim 1, wherein said energy dissipation
means comprise at least one hydraulic mechanism mounted on said
displacement structure, said at least one hydraulic mechanism
comprising at least one hydraulic cylinder including a housing and
a piston movable into and out of said housing.
7. The crash attenuator of claim 6, wherein said at least one
hydraulic cylinder includes an electronically controlled valve
having a variable orifice such that the flow of the fluid out of a
space between said piston and said housing is controlled by varying
the size of said orifice.
8. The crash attenuator of claim 1, wherein said energy dissipation
means comprise at least one inflatable airbag arranged between said
bumper and said frame, further comprising a pump for inflating said
at least one airbag with fluid.
9. The crash attenuator of claim 8, wherein said energy dissipation
means further comprise a pneumatic device having a flow line in
flow communication with an interior of said at least one airbag,
the flow of fluid through said flow line from the interior of said
at least one airbag being regulatable based on the sensed
deceleration of the object.
10. The crash attenuator of claim 1, further comprising
anticipatory sensing means for sensing impending impact of the
object with said bumper prior to actual impact of the object with
said bumper and determining information about the object, said
energy dissipation means being controlled to provide the energy
dissipation force based on the determined information about the
object.
11. The crash attenuator of claim 10, wherein said energy
dissipation means are set to provide an energy dissipation force
based on the determined information about the object prior to
actual impact of the object with said bumper.
12. The crash attenuator of claim 1, wherein said energy
dissipation means comprise at least one inflatable airbag arranged
between said bumper and said frame, further comprising a pump for
inflating said at least one airbag with fluid.
13. The crash attenuator of claim 12, further comprising
anticipatory sensing means for sensing impending impact of the
object into said bumper prior to actual impact of the object into
said bumper, and gas-injecting means responsive to the sensed
impact of the object for injecting additional gas into said at
least one airbag prior to the impact of the object.
14. The crash attenuator of claim 13, wherein said gas-injecting
means comprises a pyrotechnic material.
15. A method for protecting a truck or fixed structure from damage
resulting upon impact of a moving object with the truck or
structure, comprising the steps of: mounting a movable displacement
structure to the truck or structure, the displacement structure
having an expanded position and a contracted position, arranging a
bumper having an impact-receiving face adapted to receive the
impact from the moving object on the displacement structure,
expanding the displacement structure to its expanded position, and
dissipating at least some of the impact energy of the moving object
and reducing the velocity of the moving object by adjusting an
energy dissipation force which dissipates the impact energy of the
moving object.
16. The method of claim 15, further comprising the step of:
expanding the displacement structure after the impact energy of the
object is dissipated such that the crash attenuator is
reusable.
17. The method of claim 15, further comprising the step of: sensing
deceleration of the object after impact into the bumper, and
adjusting the energy dissipation force based on the sensed
deceleration of the object.
18. The method of claim 15, further comprising the steps of:
mounting at least one hydraulic mechanism on the displacement
structure, the at least one hydraulic mechanism comprising at least
one hydraulic cylinder including a housing and a piston movable
into and out of the housing, and adjusting the energy dissipation
force by controlling the flow of a fluid out of a space between the
piston and the housing.
19. The method of claim 15, further comprising the steps of
arranging at least one inflatable airbag on the displacement
structure; inflating the at least one airbag with fluid; and
adjusting the energy dissipation force by regulating the flow of
the fluid from the at least one airbag.
20. The method of claim 15, further comprising the steps of:
arranging at least one inflatable airbag on the displacement
structure; inflating the at least one airbag with fluid; sensing
deceleration of the object after impact into the bumper; and
initiating a pyrotechnic inflator to increase the pressure in the
airbag based on the sensed deceleration of the object.
21. The method of claim 15, further comprising the steps of:
sensing motion of the object after impact into the bumper, and
adjusting the energy dissipation force in order to decelerate the
object at a calculated rate.
22. A crash attenuator which receives an impact force from a moving
object and dissipates the impact energy of the object to thereby
reduce the velocity of the object, comprising a frame mountable to
a truck or stationary structure, a bumper having an
impact-receiving face adapted to receive the impact from the object
in a crash, a movable displacement structure coupled to said frame
and interposed between said frame and said bumper and having a
first position in which said bumper is relatively distant from said
frame and a second position in which said bumper is relatively
proximate to said frame, energy dissipation means coupled to said
displacement structure for dissipating at least some of the impact
energy of the object received by said bumper which causes said
displacement structure to be moved from the first position toward
the second position and thereby reducing the velocity of the
object, and means for sensing motion of the object after impact
with said bumper and controlling said energy dissipation means to
provide a variable energy dissipation force in order to decelerate
the object at a calculated rate.
23. A crash attenuator which receives an impact force from a moving
object and dissipates the impact energy of the object to thereby
reduce the velocity of the object, comprising a frame mountable to
a truck or stationary structure, a bumper having an
impact-receiving face adapted to receive the impact from the object
in a crash, a movable displacement structure coupled to said frame
and interposed between said frame and said bumper and having a
first position in which said bumper is relatively distant from said
frame and a second position in which said bumper is relatively
proximate to said frame, energy dissipation means coupled to said
displacement structure for dissipating at least some of the impact
energy of the object received by said bumper which causes said
displacement structure to be moved from the first position toward
the second position and thereby reducing the velocity of the
object, said energy dissipation means being arranged to provide an
energy dissipation force for dissipating the impact energy of the
object, control means for controlling the energy dissipation
force.
24. The crash attenuator of claim 23, wherein said control means
comprises a pyrotechnic inflator.
25. The crash attenuator of claim 23, wherein said energy
dissipation means comprise at least one hydraulic mechanism mounted
on said displacement structure, said at least one hydraulic
mechanism comprising at least one hydraulic cylinder including a
housing and a piston movable into and out of said housing, the flow
of a fluid out of a space between said piston and said housing
being controlled in order to vary the energy dissipation force,
said control means comprising a valve having a variable orifice
such that the flow of the fluid out of a space between said piston
and said housing is controlled by varying the size of said orifice.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/200,367 filed Nov. 23, 1998.
[0002] This application claims domestic priority of U.S.
provisional patent application Ser. No. 60/066,486 filed Nov. 24,
1997 through the '367 application.
FIELD OF THE INVENTION
[0003] The present invention relates in general to crash
attenuators, and more particularly to medium-damped crash
attenuators that use the flow of a medium such as a liquid or gas
to dissipate the energy of an object such as a vehicle impacting
the crash attenuator. Still more particularly, the invention
relates to attenuators enabling active control of the rate of
energy dissipation thereof to better control the deceleration of
vehicles impacting the attenuator having widely varying kinetic
energy.
[0004] The present invention also relates to method for protecting
fixed structures from damage caused by the impact of objects such
as vehicles, e.g., structures situated alongside highways.
BACKGROUND OF THE INVENTION
[0005] Many commercial products exist and numerous patents have
been issued directed to the design and construction of impact
attenuators or barriers to control the deceleration of an errant
vehicle as it approaches an obstruction or hazard on, or adjacent
to, a highway. Several prior art patents will be discussed below.
This invention is concerned primarily with impact attenuators that
are mounted on the rear of a construction vehicle, commonly called
truck-mounted attenuators (TMA), although it is not limited
thereto. The invention also has applicability to more permanent
attenuator installations such as those of the type used around
fixed highway structures especially where space is limited.
[0006] A review of some patents and commercial literature of TMAs
illustrates a wide variety of designs which appear to have evolved
by trial and error with little attempt to optimize the design to
handle a wide variety of impacting vehicle kinetic energies. Thus,
such existing devices generally have a fixed force versus
deflection function that provides the same resisting force to the
impacting vehicle regardless of that vehicle's mass or
velocity.
[0007] The primary purpose of a TMA is to protect construction
personnel from death or injury caused by a vehicle which mistakenly
or accidentally intrudes into a construction zone. Secondarily, the
TMA is designed to minimize the death and injury to the occupants
of the errant vehicle. Ideally, the TMA should capture the
impacting vehicle preventing it from being diverted either into
adjacent traffic or off the road where it might impact a roadside
structure such as a utility pole. Preferably, the TMA should even
decelerate the vehicle at an acceptable level, such as 15 Gs,
regardless of the mass or velocity of the impacting vehicle.
Additionally, it is desirable for the TMA to be low cost, reusable
after an impact, easily transported, light weight, easily shipped,
easily stored, etc. No TMA on the market today satisfactorily meets
all of these requirements. Therefore, there is a dire need for such
a TMA that is the subject of this invention.
[0008] It is clear from the patents and commercial literature that
many mechanisms exist for absorbing energy of an impacting vehicle
into a TMA. These include a variety of structures that depend on
the bending of metal or plastic, devices that utilize water, foam
rubber, plastic etc. in a variety of energy absorption modes.
Frequently, the energy dissipated by the system is part of the
structure of the device. In fact, the prior art inventions have
frequently confused the functions of structure and energy
absorption. The instant invention therefore centers on the
separation of these two functions of supporting structure and
energy dissipation and optimizing these functions separately.
[0009] The basic problem to be solved by a TMA design is to capture
an impacting vehicle and to decelerate it at an approximate
constant value that is relatively independent of the velocity and
mass of the impacting vehicle. It is also desirable for the
impactor to be resetable and that it can be easily collapsed for
transportation, shipping, storage etc. It is noteworthy that none
of the TMAs on the market today are reusable and therefore
invariably require replacement after an impact.
[0010] Review of the Prior Art
[0011] U.S. Pat. No. 3,674,115 to Young et al. describes a liquid
filled shock absorber comprised of many tubes each with a fixed
orifice. On impact of a vehicle into the shock absorber, the fluid
is forced to flow through the orifices which provides the energy
dissipation. Since the orifices are fixed, the system will not
adjust to vehicle impacts of varying kinetic energy to provide a
constant deceleration. Also, since the device is substantially
composed of such cylinders, it is heavy if used as a TMA. It is
designed, therefore, for use in fixed installations.
[0012] U.S. Pat. No. 4,190,275 to Mileti describes a light weight
reusable TMA which is self restoring and thus immediately available
to receive an additional impact. The impact attenuator is
constructed from a plurality of expanded plastic sheets sandwiched
between plywood stiffeners. The expanded plastic sheets form air
filled cells. The energy dissipation mechanism is not disclosed but
it appears that the energy is stored as compressed gas within the
cells rather than dissipated. Thus, there is a substantial force at
the end of the crash to cause the impacting vehicle to change its
direction and rebound at a substantial velocity off of the TMA thus
substantially increasing the velocity change of the vehicle above
the initial vehicle impact velocity. This increases the severity of
the crash and thus the potential for injury to the construction
crew and the vehicle occupants. There is no provision in this
patent to adjust the force on the impacting vehicle so that
substantially the same deceleration is achieved for vehicles of
different kinetic energy. This has the effect of substantially
increasing the length required of the device in order to handle
both light and heavy impacting vehicles at high velocities. The
first part of the TMA must be designed to decelerate a light, high
speed vehicle at a safe level. This same force is then all that is
available for the heavy vehicle which is then decelerated at a much
lower level during the initial part of the crush and then at a
higher level later.
[0013] U.S. Pat. No. 4,635,981 to Friton describes an attenuator
including a series of chambers made from sheet metal with some of
the chambers containing crushable plastic foam, which, along with
the plastic deformation of the sheet metal, dissipates the kinetic
energy of the impacting vehicle. The system is not reusable and
does not adjust to impacting vehicles having different kinetic
energies.
[0014] U.S. Pat. No. 4,674,911 to Gertz describes a crash cushion
which uses the compression of air to act as a spring to provide an
ever increasing force acting against the impacting vehicle. This
system is reusable but does not adjust to impacting vehicles having
different kinetic energies. By having the function of an ever
increasing force with displacement, it is particularly inefficient
in decelerating a vehicle where a constant force is desired.
[0015] U.S. Pat. No. 4,711,481 to Krage et al. describes an
attenuator that uses the crushing or plastic deformation of sheet
metal to provide the energy dissipation. This system is not
reusable and does not adjust to impacting vehicles having different
kinetic energies. By having the function on an ever increasing
force with displacement, it is particularly inefficient in
decelerating a vehicle where a constant force is desired.
[0016] U.S. Pat. No. 5,052,732 to Oplet et al. describes an
attenuator which uses a plurality of layers of fibrous hexagonal
elongate cells which provides energy absorption during crushing. It
suffers from the same defects at Krage et al. (U.S. Pat. No.
4,711,481).
[0017] U.S. Pat. No. 5,101,927 (Murtuza) describes an automatic
brake actuation device including a "feeler" which extends forward
of a vehicle and detects objects that the vehicle is about to
strike. Upon detecting an object, the device actuates the brakes of
the vehicle to bring the vehicle to rest. Also, upon impact with
the object, the feeler is retracted without applying any force
against such retraction. One stated object of the Murtuza invention
is to provide an improved automatic brake actuation system wherein
the extendable detector is retracted upon impacting an object. More
particularly, in the embodiment shown in FIGS. 13 and 14, the
device includes a support member 112 mounted to the vehicle and a
feeler cylinder 114 having a piston 118 therein. Movement of the
piston 118 controls expansion and retraction of a parallel-bar
expanding feeler 130. Movement of the piston is obtained by forcing
fluid into a retracting portion 128 of the cylinder 114 while fluid
is vented from the extending portion 126 and vice versa. This is
achieved by providing fluid controls to act as extending means or
devices and retracting means or devices for supplying fluid under
pressure to the feeler cylinder.
[0018] U.S. Pat. No. 5,192,157 to Laturner describes a fixed
installation vehicle crash barrier that attempts to make use of a
more efficient method of deforming metal to absorb energy. It also
suffers from the same limitations as Krage et al. (U.S. Pat. No.
4,711,481).
[0019] U.S. Pat. No. 5,199,755 to Gertz describes a TMA that also
uses the bending of metal as the main energy absorption mechanism
and thus has the same limitations as Krage et al. (U.S. Pat. No.
4,711,481).
[0020] U.S. Pat. No. 5,403,112 to Carney describes a TMA where part
of the structure is a scissors mechanism. The bending of metal is
the energy absorption mechanism and thus has the same limitations
as Krage et al. (U.S. Pat. No. 4,711,481).
[0021] U.S. Pat. No. 5,642,792 to June describes a TMA using large
drum shaped plastic cylinders to provide an energy absorption
system. The system is not reusable and does not adjust to the
kinetic energy of the impacting vehicle.
[0022] Accordingly, none of the prior art patents mentioned above
discloses a TMA having the sought after properties and thus, a
critical need exists for such a device. A central issue is that
since prior art TMAs are not optimally designed, they must be made
very long in order to handle both low and high mass vehicles at
high speed. This makes the devices expensive, difficult to maneuver
and less than optimum as a life saving device.
OBJECTS OF THE INVENTION
[0023] It is an object of the present invention to provide a new
and improved crash attenuator for mounting on a truck or a
stationary structure.
[0024] It is another object of the present invention to provide a
new and improved crash attenuator for mounting on a truck of
stationary structure which is reusable.
[0025] It is another object of the present invention to provide a
new and improved crash attenuator for mounting on a truck or a
stationary structure which adjusts to the kinetic energy of a
vehicle impacting into the same.
[0026] It is still another object of the present invention to
provide a new and improved crash attenuator for mounting on a truck
or a stationary structure which is efficient in decelerating a
vehicle impacting into the attenuator where a constant deceleration
is desired.
[0027] It is yet another object of the present invention to provide
a new and improved crash attenuator for mounting on a truck or a
stationary structure that separates the functions of the supporting
structure and the energy dissipation and optimizes these functions
separately.
[0028] It is another object of the present invention to provide a
new and improved crash attenuator for mounting on a truck or a
stationary structure which enables active control of the rate of
energy dissipation in order to better control the deceleration of
vehicles impacting the attenuator having widely varying kinetic
energy.
[0029] It is a further object of the present invention to provide a
new and improved crash attenuator for mounting on a truck or a
stationary structure which is low cost, reusable after an impact,
easily transported, light weight, easily shipped and easily
stored.
SUMMARY OF THE INVENTION
[0030] The crash attenuators in accordance with this invention are
first designed as a structural mechanism which is capable of
supporting the loads arising from the impact of a vehicle and the
resulting reaction loads arising from the truck inertial loading
and the energy dissipation or damping device. The damping device is
then designed which may be either one or more hydraulic cylinders
and/or one or more inflatable/deflatable airbags. This separates
the structural function from the energy dissipation function and
permits the optimization of each separately. In both cases, a
movable displacement structure is provided to enable movement of a
bumper having an impact-receiving face toward and away from a frame
connected to the truck or stationary structure. The displacement
structure may comprise a scissors mechanism that has an expanded
condition in which the bumper is distant from the frame and a
contracted condition in which the bumper is relatively close to the
frame. Similar scissors mechanisms have found a successful
application for cases of load lifting in industrial settings. The
energy dissipation device is coupled to the scissors mechanism and
can be either hydraulic or pneumatic, although the hydraulic design
is preferred for most applications.
[0031] This approach was only partially implemented in U.S. Pat.
No. 5,248,129 to Gertz wherein a scissors mechanism is coupled with
energy absorbing elements and in U.S. Pat. No. 5,642,792 to June
wherein a hinged support frame supports an energy absorbing
rectangular box-like structure. The preferred design of a crash
attenuator in accordance with the invention combines a scissors or
other expandable structure containing a plurality of sections,
preferably at least three or four sections, with hydraulic damping
cylinders. In a second design of a crash attenuator in accordance
with the invention, the scissors mechanism houses at least one
inflatable airbag which may be in the form of an accordion
structure with the various sections of the airbag internally
tethered for shape retention. Other shape retention means may also
be provided in connection with the airbag(s).
[0032] An electronic control module may be incorporated onto the
scissors mechanism in order to sense the motion of an impacting
vehicle and control the opening of exhaust orifices associated with
the hydraulic or pneumatic energy dissipation device in order to
achieve a substantially constant deceleration of the vehicle
regardless of the mass and velocity of the impacting vehicle. The
cross section area of the airbag(s) will be made as large as
possible in the pneumatic case in order to minimize the initial
compression of the airbag(s) before maximum pressure is obtained.
The motion sensing system may be ultrasonic, radar or lidar based,
or preferably accelerometer based. An electronically controlled
valve is used to control the flow of either the hydraulic fluid or
other medium from hydraulic cylinders in the hydraulic case, or gas
or other medium out of the airbag(s) for the pneumatic case, during
impact.
[0033] The system functions as follows. In the collapsed state, the
TMA will occupy a space of typically approximately 25% of its
expanded state making it easy to transport, store and ship. It
could occupy any amount less than about 50% of its expanded state.
This is facilitated by the use of a scissors mechanism comprises
linked members articulated to one another. Upon arrival at the work
site, a hydraulic pump in the hydraulic case, or small vacuum
cleaner type pump for the pneumatic case, will be activated to
expand the TMA to its extended state where it is ready to receive
an impact. The scissors mechanism will thus be expanded as the
hydraulic pump is actuated to extend pistons associated therewith,
the cylinder and piston of each hydraulic cylinder being connected
to different parts of the scissors mechanism, or the airbag(s)
is(are) inflated.
[0034] Bumpers at the end of the TMA, made from a material such as
polyurethane foam, provide a low level of energy absorption for low
speed impacts. At higher speeds, a deformable sub-bumper structure
can be used to help channel the vehicle into the center of the TMA
and capture it to prevent it from being deflected off of the TMA.
Accelerometers located in the rear of the bumper structure sense
the deceleration of the bumper, and thus the deceleration of the
impacting vehicle. These accelerometers send signals to the control
module, which then adjusts the valve or orifice openings to control
the fluid outflow from the hydraulic cylinders or medium outflow
from the airbag(s) and thereby vary the energy dissipation force
provided by the energy dissipation device and as a result, the
vehicle deceleration. In the hydraulic embodiment, the rate of
fluid outflow will be reflected in the movement of the piston back
into the cylinder. In this manner, the system will provide a large
energy dissipation force when the impacting vehicle is a heavy
vehicle and a lower energy dissipation force for light vehicles,
thus approximately stopping both types of vehicles in the same
distance for the same velocity of impact. This permits a more
efficient utilization of the available crush space and thus
minimizes the size of the TMA.
[0035] Some loss of efficiency results from the initial
compressibility of the gas in the airbag for the pneumatic case.
However, calculations set forth in Appendix 1 show that this loss
of efficiency is manageable without greatly increasing the length
of the TMA if atmospheric pressure is used. To the extent that the
airbag can be pressurized, this effect will become smaller. Other
energy absorption mechanisms that provide a force in parallel at
least during the compression stage can of course be added to help
compensate for this compressibility effect.
[0036] Another concern of the pneumatic system is in the compliance
of the airbag itself. Once again, calculations indicate that this
should not be a significant problem if the airbag is properly
designed. In some cases, an accordion design with simple tethering
will prove to be insufficient and a design based on a self-shaping
airbag design, as disclosed in U.S. Pat. No. 5,653,464 incorporated
herein by reference, which solves the problem by properly shaping
the airbag to cause it to naturally take on the desired shape.
[0037] Although the preferred design uses electronics to control
the valve associated with the hydraulic cylinders or orifice
opening(s) associated with the airbag(s), other variations include
the use of a mechanical system to sense the acceleration and
control the opening of the flow restrictors, i.e., the valve or
orifice openings. This results in an all-mechanical system by
eliminating the electronics. The all-mechanical system is
particularly applicable for fixed installations in addition to
truck mounted applications.
[0038] In one method for protecting a truck or fixed structure in
accordance with the invention, a movable displacement structure is
mounted to the truck or structure and has an expanded position and
a contracted position. A bumper having an impact-receiving face
adapted to receive an impact from an object in a crash is arranged
on the displacement structure. The displacement structure is
preferably stored and transported in its contracted condition and
when readied for use, it is expanded to its expanded position. In
use, impact of an object into the bumper which causes the
displacement structure to be moved from the expanded position
toward the contract position is sensed and at least some, if not
all, of the impact energy of the object is dissipated by adjusting
an energy dissipation force such that the object is brought to
rest. In some preferred embodiments, the displacement structure may
be expanded after the impact energy of the object is dissipated
such that the crash attenuator is reusable.
[0039] It is possible to sense deceleration of the object after
impact into the bumper and adjust the energy dissipation force
based on the sensed deceleration of the object. The hydraulic and
pneumatic systems described herein may be applied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The invention will be described with reference to the
accompanying non-limiting drawings wherein:
[0041] FIG. 1 shows a first embodiment of a crash attenuator in
accordance with the invention in its contracted condition;
[0042] FIG. 2 shows an enlarged view of the first embodiment of the
crash attenuator in accordance with the invention in its contracted
condition;
[0043] FIG. 3 shows the first embodiment of the crash attenuator in
accordance with the invention in its expanded condition;
[0044] FIG. 4 shows another view of the first embodiment of the
crash attenuator in accordance with the invention in its expanded
condition;
[0045] FIG. 5 shows a second embodiment of a crash attenuator in
accordance with the invention in its expanded condition;
[0046] FIG. 6 shows the airbag used in the second embodiment of the
crash attenuator in accordance with the invention; and
[0047] FIG. 7 shows a modified embodiment of the crash attenuator
in accordance with the invention having an accordian design for the
airbag.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Referring to the accompanying drawings wherein like
reference numerals refer to the same or similar elements, FIGS. 1-4
show a first embodiment of a crash attenuator in accordance with
the invention denoted generally as 10. The crash attenuator 10 is
mounted to a vehicle such as a truck 12, most often so that it
faces rearward of the truck 12. As such, it will protect the truck
12 from damage resulting from a vehicular impact from the rear of
the truck 12. The crash attenuator 10 is secured to the truck 12 by
conventional mounting means, e.g., bolts, screws, welding,
clamps.
[0049] The typical size of the crash attenuator 10 when mounted to
a standard size truck is about eight feet wide, fifteen feet long
and two and one half feet high in the expanded condition. The crash
attenuator 10 is preferably designed so that the center of pressure
is about 23 inches off ground.
[0050] The crash attenuator 10 includes a rigid frame 14 comprising
a pair of spaced apart, parallel beams 16 extending substantially
perpendicular to the rear of the truck 12, a cross beam 18 for
connecting the beams 16 to provide stability thereto and a rigid
support beam structure 20 arranged at a rearward end of the beams
16 and connected thereto. Beams 16 are connected to a suitable
surface of the truck 12. A diagonal beam 22 is arranged at each
side of the frame 14 (only one of which is shown) and is connected
to the beam structure 20 to provide stability for the same. The
beam structure 20 comprises an upper horizontal beam 24, a lower
horizontal beam 26 parallel to the upper horizontal beam 24 and
spaced therefrom and three spaced apart, parallel vertical beams 28
connecting the upper and lower horizontal beams 24, 26. A
substantially rigid plate 30 is connected to one or more of the
beams 24, 26, 28 and serves as a connecting surface to which ends
of the beams 16 and 22 are attached. The connections between the
beams and plates, which are preferably made of a metal material,
may be in any suitable manner, e.g., by welds, screws, etc.
[0051] FIGS. 1 and 2 show the crash attenuator 10 in its compressed
or contracted condition or position that is also the storage and
transport position and is as small as 25% of the length of the
crash attenuator in its expanded condition or position. Generally,
the length of the crash attenuator 10 in its contracted state can
be 50% or less of the length in its expanded state. To enable the
expansion or extension of the crash attenuator 10, the crash
attenuator 10 includes a movable displacement structure such as a
scissors mechanism 32 which comprises a plurality of elongate
members 34a-34h on each side of the crash attenuator 10 (FIG. 3).
Elongate members 34 are substantially rigid and have a rectangular
body section and projecting links 36 at each end. Member 34a is
connected via its link 36 at its upper end to a link 38 which in
turn is connected to a link 40 fixedly mounted on the upper
horizontal beam 24 of the beam structure 20. The connection between
the links 36, 38, 40 is designed so that each link is rotatable
relative to each of the links connected therewith, e.g., through a
pin 42 extending through each pair of connected links and defining
a pivot axis. As such, link 36 and thus member 34a can rotate
relative to link 38 and link 38 is also rotatable relative to link
40 so that as a result, the lower end of member 34a is swingable
outward away from the beam structure 20 by virtue of the rotation
of the link 36 at the upper end of member 34a relative to the link
38 which in turn is rotatable relative to the link 40. In a similar
manner, member 34b is movably coupled to the lower horizontal beam
26 via links 36a, 38a, 40a so that the upper end of member 34b is
swingable outward away from the beam structure 20. A pin 44 is
arranged at the center point of the members 34a, 34b to connect the
same while enabling rotation of both members 34a, 34b, i.e., both
members are rotatable about the axis defined by the pin 44.
[0052] Member 34c is connected to member 34a via the links 36 at
the lower end of each member whereby a pin 45 extends through the
links to enable rotation of both members 34a, 34c about the axis
defined by the pin. Member 34e is connected to member 34c via the
links 36 at the upper end of each member whereby a pin extends
through the links to enable rotation of both members 34c, 34e about
the axis defined by the pin. Member 34e is connected to member 34g
via the links 36 at the lower end of each member whereby a pin
extends through the links to enable rotation of both members 34e,
34g about the axis defined by the pin.
[0053] Member 34b is connected to member 34d via the links 36 at
the upper end of each member whereby a pin extends through the
links to enable rotation of both members 34b, 34d about the axis
defined by the pin. Member 34f is connected to member 34d via the
links 36 at the lower end of each member whereby a pin extends
through the links to enable rotation of both members 34d, 34f about
the axis defined by the pin. Member 34h is connected to member 34f
via the links 36 at the upper end of each member whereby a pin
extends through the links to enable rotation of both members 34f,
34h about the axis defined by the pin.
[0054] Overall, by means of the links 36 and pins connecting
adjoining links 36, the scissors mechanism 32 is movable between
the contracted position shown in FIGS. 1 and 2 and the expanded
position shown in FIGS. 3 and 4. The scissors mechanism 32 should
be sufficiently rigid and sturdy to maintain a bumper 70 arranged
at the end of the scissors mechanism 32 at a desired level from the
ground without excessive sag. Note that in general permanently
lubricated journal bearings are used at each rotation joint which
is the convention in the art. Naturally, other types of bearings
such as ball or roller bearings can also be used.
[0055] Bumper 70 as shown in FIG. 1 is a flat plate. In FIGS. 2-5,
the bumper 70 is shown as a rather, large bumper, additional
details of the construction of which are provided below.
[0056] In the embodiment shown in FIGS. 1-4, a support structure is
included for supporting a hydraulic system which facilitates the
expansion and contraction of the attenuator 10 and also enables the
controlled contraction of the attenuator after a crash to enable
the attenuator to be responsive to the kinetic energy of the
impacting vehicle, i.e., provide a variable resistive or energy
dissipation force depending on the mass and velocity of the
impacting vehicle.
[0057] To this end, pin 44 is formed integral with or connected to
a transverse rod 46 that extends from one side of the crash
attenuator 10 to the other side. At the other side of the crash
attenuator 10, the rod 46 is connected to or formed integral with
the pin connecting the corresponding members 34a, 34b at that side.
A pin 48 is also arranged at the center point of the members 34c,
34d to connect the same while enabling rotation of both members
34c, 34d, i.e., both members are rotatable about the axis defined
by the pin 48. Pin 48 is formed integral with or connected to a
transverse rod 50 that extends from one side of the crash
attenuator 10 to the other side. At the other side of the crash
attenuator 10, the rod 50 is connected to or formed integral with
the pin connecting the corresponding members 34c, 34d at that side.
A pin 52 is also arranged at the center point of the members 34e,
34f to connect the same while enabling rotation of both members
34e,34f, i.e., both members are rotatable about the axis defined by
the pin 52. Pin 52 is formed integral with or connected to a
transverse rod 54 that extends from one side of the crash
attenuator 10 to the other side. At the other side of the crash
attenuator 10, the rod 54 is connected to or formed integral with
the pin connecting the corresponding members 34e, 34f at that side.
Similarly, a pin 56 is arranged at the center point of the members
34g, 34h to connect the same while enabling rotation of both
members 34g, 34h, i.e., both members are rotatable about the axis
defined by the pin 56. Pin 56 is formed integral with or connected
to a transverse rod 58 that extends from one side of the crash
attenuator 10 to the other side. At the other side of the crash
attenuator 10, the rod 58 is connected to or formed integral with
the pin connecting the corresponding members 34g, 34h at that
side.
[0058] Rods 46, 50, 54, 58 thus constitute a support structure for
the energy dissipation system described below. Other support
arrangements are of course encompassed within the invention without
deviating from the scope and spirit thereof. Rods 46, 50, 54, 58
are shown as being elongate and substantially cylindrical. However,
it is pointed out that the rods 46, 50, 54, 58 may be any shape
whatsoever and further, that not all of the rods are required,
i.e., it is possible to dispense with one or more of the rods
connecting the pins on opposite sides of the crash attenuator 10.
Also, each of the transverse rods may be formed integral with the
associated pins.
[0059] In the embodiment shown in FIGS. 1-4, the energy dissipation
system is a hydraulic actuating mechanism 100 arranged in
connection with the scissors mechanism 32 and which serves to
expand and contract the same. Hydraulic actuating mechanism 100 is
designed to provide an energy dissipation force to dissipate at
least some, if not all, of the energy of the vehicle impacting the
bumper by controlling the contraction or compression of the
scissors mechanism 32, i.e., the movement of the scissors mechanism
32 from its expanded condition shown in FIGS. 1 and 2 toward its
contracted condition shown in FIGS. 3 and 4. The energy dissipation
force is ideally adjustable and determined, e.g., based on the
kinetic energy of the impacting vehicle.
[0060] To mount the hydraulic actuating mechanism 100, at each side
of the crash attenuator 10, a mounting plate 61 is attached to the
transverse rod 46 and a mounting plate 63 is attached to transverse
rod 58. Mounting plates 61, 63 may be formed with a projecting part
having an aperture designed to receive the respective rod 46, 58. A
pair of actuators 60 are coupled to the mounting plate 61 and via
rigid mounting links 65 to transverse rod 50. Similarly, a pair of
actuators 64 are coupled to mounting plate 63 and via rigid
mounting links 67 to transverse rod 54. Mounting links 65, 67
include an aperture designed to receive the respective transverse
rod 50, 54. Each actuator 60, 64 includes a cylinder having a
hollow interior, a piston rod which is movable within the interior
of the cylinder and means for passing a fluid into the hollow
interior into a space between a head of the piston rod and an end
of the cylinder so as to cause the piston to move outward from the
cylinder when the fluid is passed into the space and to move back
into the cylinder when the fluid is removed from the space. The
construction of the cylinders is conventional. Actuators 60 each
have a piston rod 62 that is connected to the mounting plate 61,
whereas the cylinder itself is connected to mounting links 65. In a
like manner, actuators 64 each have a piston rod 66 which is
connected to the mounting plate 63, whereas the cylinder itself is
connected to mounting links 67.
[0061] The actuators 60, 64 are positioned so as not to interfere
with the transverse rods 46, 50, 54, 58 when the scissors mechanism
32 is in its contracted position. Thus, as shown in FIGS. 3 and 4,
the actuators 60, 64 are situated above and below the transverse
rods 46, 50, 54, 58 that are essentially in the same horizontal
plane. Also, by virtue of the connections of the cylinders of the
actuators 60, 64 to the transverse rods 50, 54 and the connection
of the piston rods 62, 66 to the mounting plates 61, 63, which are
connected to the transverse rods 46, 58, the transverse rods 54, 58
are movable relative to each other upon actuation of the actuators
64 and the transverse rods 46, 50 are movable relative to each
other upon actuation of the actuators 60.
[0062] In operation, the piston rods 62, 66 start out housed within
the respective cylinder 60, 64 as shown in FIGS. 1 and 2.
Thereafter, when it is desired to expand the scissors mechanism 32,
a hydraulic medium is directed into the actuators 60, 64 to force
the respective piston rod 62, 66 out of the interior of the
cylinder. In this manner, the transverse rods 46, 50, 54, 58 are
moved apart from one another which causes the members 34a-34h to be
forced into the expanded position shown in FIGS. 3 and 4 in view of
the connection between the transverse rods 46, 50, 54, 58 and the
members 34a-34h via the pins connecting the center regions of
crossing members.
[0063] Note that the hydraulic hoses and reservoirs have not been
shown in the drawings in order to permit the concepts to be more
easily understood.
[0064] Although a scissors mechanism has been illustrated for the
supporting structure in the above-described embodiment, other
linkage designs would also work for some applications without
deviating from the scope and spirit of the invention. Thus, instead
of the scissors mechanism described above, other collapsible
structures composed of a plurality of members arranged to provide
the collapsible structure with a contracted position and an
expanded position may be used. Such structures could include
members linked and articulated to one another. One such design uses
a bifold door type structure, using hinged vertical frames, and
another is based on 4-bar linkages. Although a vertical scissors
structure has been illustrated employing two such structures, in
some applications as many as four or more such mechanisms are used.
Similarly, although the scissors are shown lying in a vertical
plane, they can be combined with scissors mechanisms that are on
top and bottom of the device, or, alternately, only horizontal
scissors mechanisms are used with appropriate vertical bracing.
Even with the illustrated design, many types of cross bracing can
be added as needed.
[0065] A variety of added supporting structures or apparatus could
be used including wheels and cables. The system may even be
designed to deflect downward when impacted so as to obtain some
support from the ground. This would also add a certain amount of
lateral stability to the system.
[0066] The crash attenuator 10 also comprises a bumper 70 mounted
via links 72 to the upper link 36 of members 34g and via links 74
to the lower link 36 of members 34h. Bumper 70 is made from a
material that can provide a low level of energy absorption for low
speed impacts, such as polyurethane foam. The extreme rear end of
the bumper 70 may include reflectors 76. Bumper 70 may also be made
of fibrous hexagonal elongate cells, or a series of chambers made
from sheet material, or any other known construction for providing
energy absorption.
[0067] To provide the damping of the crash attenuator 10 during a
crash, the hydraulic actuating mechanism 100 includes control means
associated with the actuators 60, 64 for controlling the release of
fluid therefrom, the release of fluid from the actuators 60, 64
determining the movement of the piston rod 62, 66 back into the
respective cylinder and thus the energy dissipation force effective
to decelerate the vehicle. Initially, in the expanded condition,
the actuators 60, 64 include enough fluid to provide for the
desired length of the attenuator 10, and thus in a crash, some of
this fluid will be released. The hydraulic actuating mechanism 100
may comprise a valve having a variable opening or variable size
orifice through which the fluid from the actuators 60, 64 flows. An
electronic control module 80 is arranged at the rear of the bumper
70 to detect the deceleration of the vehicle and is coupled to
control means for the valve. Accordingly, the orifice of the valve
has an initial size that will result in a predetermined outflow of
fluid from the actuators 60, 64 and thus a predetermined energy
dissipation force to the impacting vehicle. If the electronic
control module 80 determines that the deceleration of the vehicle
is too rapid or too slow, it adjusts the size of the orifice to
obtain a desired deceleration rate of the vehicle. As such, by
adjusting the size of the orifice, the attenuator 10 provides a
substantially constant deceleration rate of all vehicles regardless
of their mass and velocity. Alternately, once the mass and velocity
of the impacting vehicle has been determined, the control module 80
can adjust the deceleration of the impacting vehicle so as to use
up nearly all of the stroke of the TMA. In this manner, injury to
the vehicle occupants, damage to the impacting vehicle and risk of
airbag deployment is minimized especially for low velocity
crashes.
[0068] FIG. 5 shows a pneumatic system 110 for providing an energy
dissipation force for dissipating the energy from the impact of the
vehicle into the attenuator 10A. The pneumatic system 110 comprises
one or more inflatable airbags 112 defined by a material 114, and
if a plurality of such compartments is provided, then the
compartments may be fluidly separated from one another or coupled
to one another. The scissors mechanism 100 is essentially the same
as that described above with respect to FIGS. 1-4, except that the
transverse rods 46, 50, 54, 58 are not provided since it is not
necessary to couple actuators to the same. Rather, the links 36 at
the ends of each member 34a-34h are mounted to intermediate
supports 116 and the material 114. Tethers 118 may also be provided
to maintain a desired shape of the airbags 112.
[0069] The airbag 112 is closed and to this end, has a face at one
end adjoining the plate 30 of the beam structure 20 connected to
the truck 12 and a face at an opposite end connected to the bumper
70. A pneumatic device 120 is arranged on the frame 14 and has an
outlet into the airbag 112. To initially expand the airbag 112, the
pump is activated to direct air or another medium into the airbag
112. The outlet from the pneumatic device 120 has a variable size
and the pneumatic device 120 is also designed to allow outflow of
air from the airbag 112.
[0070] In a crash, the airbag 112 will experience a controlled
deflation thereby providing a desired deceleration to a vehicle
impacting the attenuator 10A regardless of that vehicle's mass and
velocity. To this end, the electronic control module 80 is arranged
on the rear of the bumper 70 and senses deceleration of the
vehicle, as conveyed through the bumper 70. The outlet of the
pneumatic device 120 has an initial size which allows air to be
expelled from the airbag 112 reducing the pressure in the airbag
112 yet still enabling the airbag 112 to provide a energy
dissipation force to the impacting vehicle and decelerate the same.
If the deceleration rate of the vehicle is too high or too low,
i.e., beyond safe ranges, as detected by the electronic control
module 80, then the electronic control module 80 causes an
adjustment in the size of the outlet of the pneumatic device 120,
i.e., increases or decreases the same. In this manner, the airbag
will deflate at a controlled rate, or more appropriately maintain a
specific pressure in order to decelerate the impacting vehicle at
the desired rate.
[0071] The airbag 112 may be made with tethers 118 alone to provide
its shape in its expanded condition, without any intermediate
supports.
[0072] As shown in FIG. 7, the airbag 112 may be encased within an
accordian like housing 122 which thus serves to provide the shape
of the airbag 112. In this embodiment, the scissors mechanism 126
only comprises two expanding sections and a bumper 124 having a
concave face for directing the vehicle into the center of the crash
attenuator.
[0073] Energy Absorption
[0074] Although the hydraulic system shown in FIGS. 1-4 is
preferred, the pneumatic system shown in FIGS. 5-7 has some
advantages especially where space is not as limited. A large airbag
that can be injected with additional gas just prior to an impact,
possibly in response to the anticipatory sensing of a vehicle about
to impact the attenuator, also partially solves the loss of space
problem which occurs due to the compressibility of air during
impact. Alternately, a sacrificial plastically deformable metal
structure can be provided to compensate for the compression of the
air during the initial stages of the impact. The design of such
structures is known in the art but their use in this manner is
unique.
[0075] Both the hydraulic and the pneumatic systems can be affected
by the mass of the TMA structure. This may or may not be an
advantage and in some cases it is desirable to add additional mass
which must be accelerated by the impacting vehicle as part of the
system. The crush characteristics of the impacting vehicle should
also be taken into account in the design of the TMA The vehicle
crush has the effect of giving a lower deceleration during the
initial portion of the impact and a higher deceleration in the
later portion when the vehicle is subjected to a constant force.
This should be compensated for in the TMA algorithm since the
sensing system 80 measures the deceleration of the front of the
impacting vehicle rather than, as desired, its center of
gravity.
[0076] Interception of Impacting Vehicle
[0077] Current TMAs make little provision for effecting the
trajectory of the impacting vehicle. This is important since it is
not desirable to deflect the vehicle off of the TMA if this can be
avoided. Such a deflection could result in further accidents by
allowing the impacting vehicle to leave the road and impact a tree,
for example, or direct it into the path of oncoming traffic. When
possible, therefore, the impacting vehicle should be captured by
the TMA.
[0078] In accordance with the invention, means for guiding the path
or trajectory of the object after impact into the bumper may be
provided. For example, this can be done to some extent through the
design of the TMA where the sides of the bumper 70 are made stiffer
than the center. As shown in FIGS. 2-5, this is achieved by forming
a recessed area 78 in the center region of the bumper 70 facing the
impacting vehicle. In the alternative, in some cases it is
desirable to provide wing-like structures, which extend laterally
beyond the TMA, to further guide the vehicle into the center of the
TMA.
[0079] Additionally, some local structure associated with the end
of the TMA that is impacted can be designed to grab the impacting
vehicle to prevent it from sliding off of the face of the TMA. One
example of such a structure is shown in FIG. 7 wherein the bumper
124 is concave.
[0080] An alternate solution is to permit local plastic deformation
of the face of the TMA so that it conforms to the surface of the
impacting vehicle to oppose sliding of the vehicle off of the TMA
face. This will result in some permanent "damage" to the TMA face.
In this case, the face should be made as a replaceable part.
[0081] Electronics & Functional
[0082] The TMA is designed to provide a constant deceleration to
any object that impacts it. This design deceleration is a
particular value that is chosen to minimize injuries to vehicle
occupants. A potential problem exists in that the deceleration must
also be sufficient to trigger deployment of the airbags within the
vehicle. This poses a problem since the airbag crash sensor
algorithms are generally considered proprietary and therefore are
unknown to the TMA designer. The TMA designer must be careful that
an optimum design of one safety system does not defeat another
safety system and thereby result in more injury than would
otherwise occur.
[0083] Basically, if the TMA is designed to provide a constant
deceleration of typically 15 Gs, for example, the force exerted
onto the vehicle by the TMA should be proportional to the mass of
the impacting vehicle regardless of its impacting velocity. Since
the mass of possible impacting vehicles varies by a factor of three
or more, the TMA must be capable of supplying forces having a
similar variation in magnitude. This is accomplished by having
sensors that are capable of sensing the deceleration of the
impacting vehicle as described above. Sensor technologies which are
capable of this function include mechanical seismic devices, radar,
accelerometers, string potentiometers, laser optical ranging
sensors (lidar), ultrasonic ranging sensors, and mechanical probes,
among others. Although the preferred embodiment uses sensors that
sense the deceleration of the impacting vehicle, or the face of the
TMA which is assumed to approximately represent the impacting
vehicle, anticipatory sensing using a neural network derived
algorithm can also be used beneficially. In all cases, in the
instant invention the sensors provide information to the control
module which adjusts the opening of the airbag valve or the
hydraulic cylinder orifices (the flow restrictors) to adjust the
force of the TMA face against the vehicle to achieve the desired
constant deceleration.
[0084] It is believed that the invention disclosed herein is the
first adaptive crash attenuator system. Namely, it is believed that
it is the first system to vary the force of the impactor against
the impacting vehicle in response to the vehicle deceleration. It
is the first electronic system applied to impactors. It is also the
first adjustable or adaptive impact attenuator system.
[0085] Restrictor
[0086] The restrictor which is used to control the flow of the
fluid from the airbag(s) (pneumatic embodiment shown in FIGS. 5-7)
or the fluid from the actuators 60, 64 (hydraulic embodiment shown
in FIGS. 1-4) is an important part of this invention. The size of
the restrictor opening, along with the pressure within the chamber,
determines the flow of the fluid out of the airbag(s) or hydraulic
cylinders. This in turn determines the force that the TMA applies
to the impacting vehicle and thus the deceleration of the impacting
vehicle. The size of the restrictor opening is determined by an
actuator and associated Electronic Control Unit (ECU) 80 that
contains a microcomputer and associated algorithm. In operation,
accelerometers coupled to the ECU 80 first determine that the
impact-receiving face of the TMA is being impacted as the face
initially achieves the velocity of the impacting vehicle. The TMA's
impact-receiving face, and the impacting vehicle, then begin
decelerating at substantially the same rate, which deceleration is
measured by the accelerometers or other types of sensors as
described above. The accelerometer or other sensor signal(s) is/are
fed into the ECU, which determines the rate of deceleration of the
face and vehicle. If this rate is above the predetermined value,
the restrictor is opened allowing more fluid to flow out which
reduces the pressure in the chamber (hydraulic cylinder or airbag)
and thus reduces the resistive force of the TMA repelling or
opposing the movement of the impacting vehicle. If the deceleration
is too great, that fact is determined by the ECU and the restrictor
opening is made smaller to reduce the outflow of fluid from the
chamber in the hydraulic actuators 60, 64 (FIGS. 1-4) or airbag(s)
112 (FIGS. 5-7). In this manner, the deceleration of the TMA face
and thus the impacting vehicle is controlled to the prescribed,
predetermined value.
[0087] The algorithm in the ECU includes corrections for the mass
and thus the dynamics of the truck on which the TMA is mounted as
well as, to the extent possible, for the crush of the impacting
vehicle. In some implementations when multiple accelerometers or
other sensors are present permitting a measurement of the rotation
of the vehicles, that fact can also be taken into account in the
algorithm and used to more accurately adjust the restrictors to
attempt to reduce the vehicle rotation.
[0088] Pressurization (Pneumatic Case)
[0089] For the pneumatic case shown in FIGS. 5-7, the airbag(s) 112
is/are expanded when the truck arrives at the work site using a
pump or other pneumatic pressurizing device 120 such as a vacuum
cleaner type pump or a small turbine. If desired, the pump can
increase the airbag pressure to a value above atmospheric pressure
thereby reducing the compressibility effects described above.
Additionally, if an anticipatory crash sensor such as a radar or
lidar system is used, or another sensor or sensor system (which may
be based on pattern recognition techniques) which will detect the
impending impact of a vehicle into the attenuator 10A, a
pyrotechnic inflator can also be employed which will substantially
increase the pressure in the airbag immediately prior to the impact
in much the same manner as interior airbag inflators supply gas to
a driver or passenger airbag during a crash. Instead of a
pyrotechnic inflator, other available inflators can also be used.
The pressure in the airbag should be about 15 psi, which may be
achieved by using a pump, a compressor, a turbine and/or by heating
a gas using an inflator after impact has been predicted by, for
example, an anticipatory sensor, or after the impact has started
(the impact has been detected).
[0090] Applications
[0091] The primary application for the TMA of this invention is for
mounting onto movable platforms such as trucks to provide
protection for highway work crews. Naturally, the teachings are
also applicable to fixed installations especially where there is
limited available space. This invention is the first "smart" crash
attenuator which adjusts the restraining force automatically in
response to the kinetic energy of the impacting vehicle or object.
The application of such sensing systems to other safety barriers
will now be possible and, thus, the invention disclosed here is not
limited to crash attenuators. In particular, in many cases there is
insufficient space to deploy even the attenuators described herein
in their expanded state and thus anticipatory sensing, i.e.,
sensing an impending impact of a vehicle into the attenuator,
coupled with pyrotechnic inflators may be used to permit an airbag
crash attenuator to be deployed in anticipation of a crash to
cushion an impacting vehicle. This is the first use of an airbag
mounted on a fixed structure which inflates to cushion the impact
of a vehicle. Alternatively, in the hydraulic embodiment shown in
FIGS. 1-4, the hydraulic cylinders 60, 64 may be actuated to extend
the scissors mechanism upon a determination of an impending crash
by an anticipatory sensor system.
[0092] Such a device will find wide application along with the
development of smart highways where vehicles are automatically
guided at high speeds. On such highways, a vehicle may suffer a
catastrophic failure and go out of control. An anticipatory sensor
with a deployable crash attenuator would then cushion the impact of
the troubled vehicle. For the cases of anticipatory sensors, a
neural network based algorithm such as disclosed in U.S. patent
application Ser. No. 08/247,760 may be used.
[0093] Other Advantages
[0094] A key advantage of the attenuators of this invention is that
they are for the most part collapsible to a length substantially
shorter than their expanded or deployed length. In some cases, the
collapsed length is less than about 25% of the expanded length.
This permits the attenuator to be easily stored, shipped and
transported to the work site. To decrease their length, current
TMAs are rotated into a vertical position during transportation to
the work site. This not only requires expensive hydraulic apparatus
to be mounted onto the vehicle to provide the power to rotate the
TMA to and from the vertical position but it also limits the length
of the TMA and thus the degree of protection afforded by the
device.
[0095] The attenuator of the present invention also has a
relatively lighter weight than current attenuators of comparable
capacity. This is a result of the structural optimization in the
design of this invention.
[0096] Finally, providing the attenuator is impacted within its
design capabilities, the device can be reused shortly after an
impact.
[0097] Although several preferred embodiments are illustrated and
described above, there are possible combinations using other
geometries, sensors, materials and different dimensions for the
components that perform the same functions. This invention is not
limited to the above embodiments and should be determined by the
following claims.
[0098] It will be understood that numerous modifications and
substitution can be made to the above-described embodiments without
deviating from the scope and spirit of the invention. Accordingly,
the above-described embodiments are intended for the purpose of
illustration and not as limitation.
[0099] The preferred embodiments of the invention are described
above and unless specifically noted, it is the applicants'
intention that the words and phrases in the specification and
claims be given the ordinary and accustomed meaning to those of
ordinary skill in the applicable art(s). If applicants intend any
other meaning, they will specifically state they are applying a
special meaning to a word or phrase.
[0100] Likewise, applicants' use of the word "function" here is not
intended to indicate that the applicant seeks to invoke the special
provisions of 35 U.S.C. .sctn.112, sixth paragraph, to define their
invention. To the contrary, if applicant wishes to invoke the
provisions of 35 U.S.C..sctn.112, sixth paragraph, to define his
invention, he will specifically set forth in the claims the phrases
"means for" or "step for" and a function, without also reciting in
that phrase any structure, material or act in support of the
function. Moreover, even if applicant invokes the provisions of 35
U.S.C. .sctn.112, sixth paragraph, to define his invention, it is
the applicant's intention that his inventions not be limited to the
specific structure, material or acts that are described in the
preferred embodiments herein. Rather, if applicant claims his
inventions by specifically invoking the provisions of 35 U.S.C.
.sctn.112, sixth paragraph, it is nonetheless his intention to
cover and include any and all structure, materials or acts that
perform the claimed function, along with any and all known or later
developed equivalent structures, materials or acts for performing
the claimed function.
Appendix 1
Analysis of Air-Damped Truck Mounted Attenuator (AD-TMA)
[0101] The AD-TMA in accordance with the invention s a buffer that
is positioned behind a highway truck to absorb some or all of the
energy of an impacting vehicle. In certain embodiments, the buffer
is a substantially rectangular airbag that is designed to bring the
speed of the impactor (which is most likely an impacting vehicle)
to the speed of the highway truck by the time the airbag is fully
collapsed. Initially, the highway truck is at rest with the
transmission in gear and the brake set. After impact, the energy
absorption occurs in 4 stages: in the first stage, the truck
remains stationary and the pressure in the buffer increases as the
buffer shortens. At the end of the first stage, the pressure in the
buffer is high enough that the force the buffer exerts on the truck
overcomes the friction between the truck tires and the road, and
the truck begins to slide forward. During the second stage, the
buffer continues to shorten, its pressure continues to build, and
the impactor and truck are both moving. At the end of the second
stage, the pressure reaches its maximum value. The third stage is
similar to the second except that a vent valve opens to allow air
to flow out of the buffer at a rate such that the pressure remains
constant. At the end of the third stage, the buffer is completely
collapsed and the impactor and truck are moving at the same speed.
In the fourth stage, the impactor and truck move together and both
come to rest due to the friction between the truck tires and the
road.
[0102] For the analysis the following parameters are
introduced:
[0103] W.sub.T=weight of highway truck,
[0104] W=weight of impactor,
[0105] x=displacement of impactor after the impact,
[0106] X.sub.T=displacement of highway truck after impact,
[0107] L=initial (uncompressed) length of buffer,
[0108] A=cross-section area of buffer (remains constant),
[0109] V=volume of buffer=A( L-x+X.sub.T),
[0110] p=absolute pressure in the buffer,
[0111] P.sub.a=initial (atmospheric) pressure,
[0112] P.sub.1=pressure at end of stage 1,
[0113] P.sub.2=pressure at end of stage 2 (maximum),
[0114] .mu.=coefficient of friction between truck tires and
road,
[0115] .gamma.=ratio of specific heats of air.
[0116] Equations
[0117] In Stages 1, 2 and 3 1 W g x = - A ( p - p a ) , ( 1 )
[0118] In Stage 1
X.sub.T=0 (2)
[0119] In Stages 2 and 3 2 W T g x T = A ( p - p a ) - W T , ( 3
)
[0120] In Stages 1 and 2 3 p = ( p a ( L L - x + x T ) ) , ( 4
)
[0121] In Stage 3
p=p.sub.2 (5)
[0122] Initially
x=x.sub.T=0{dot over (x)}={dot over (x)}.sub.0, {dot over
(x)}.sub.T=0 (6)
[0123] At the end of Stage 1 A
(p.sub.1-p.sub.a)=.mu.W.sub.T (7)
[0124] At the end of Stage 3
x-x.sub.T=L, dx/dt=dx.sub.T/dt (8)
[0125] Stage 1
[0126] Equation (7) yields 4 p 1 = p a ( 1 + W T p a A ) , ( 9
)
[0127] and then (4) and (2) give 5 x 1 L = 1 - ( 1 + W T p a A ) -
1 / ( 10 )
[0128] Equation (1) with (4) and (2) can be integrated and then
Equation (9) used to get 6 x . 1 2 = x . 0 2 - ( 2 g W ) ( W T ( L
- x 1 ) - Ap a x 1 - 1 ) . ( 11 )
[0129] Stage 2
[0130] Equations (1), (3), and (4) can be combined and integrated
to yield 7 ( x . 2 - x . T2 ) 2 = x . 1 2 - 2 gA ( 1 W + 1 W T ) [
( p 2 - 1 + p a ) ( L - x 2 + x T2 ) - ( p 1 - 1 + p a ) ( L - x 1
) ] + 2 g [ ( L - x 2 + x T2 ) ] ( 12 )
[0131] and Equation (4) gives 8 p 2 = p a ( L - x 2 + x T2 L ) - (
13 )
[0132] Stage 3
[0133] Here 9 ( x 2 - x T ) = - gA ( 1 W + 1 W T ) ( p 2 - p a ) +
g = constant .
[0134] This can be integrated twice and conditions (8) used to get
10 ( x 2 - x T2 ) 2 = [ 2 gA ( 1 W + 1 W T ) ( p 2 - p a ) - 2 g ]
( L - x 2 + x T2 ) ( 14 )
[0135] and when this is combined with Equations (12) and (13), 11 -
1 ( 1 W + 1 W T ) p a AL ( L - x 2 + x T2 L ) - ( - 1 ) = x . 1 2 2
g + A ( 1 W + 1 W T ) ( p 1 - 1 + p a ) ( L - x 1 ) + ( L - x 1 ) (
15 )
[0136] Also, 12 x . - x . T = ( x . 2 - x . T2 ) L - x + x T L - x
2 + x T2 ( 16 )
[0137] during Stage 3.
[0138] Now when W, W.sub.T, A, L, {dot over (x)}.sub.0, .mu.,
.gamma., p.sub.a, and g are given, x.sub.1, p.sub.1, {dot over
(x)}.sub.1, x.sub.2.multidot.x.sub.T2, pd.sub.2, and {dot over
(x)}.sub.2- {dot over (x)}.sub.T2 can be calculated.
[0139] The final step is to calculate the orifice size needed to
maintain constant pressure during Stage 3. First, assuming
adiabatic conditions (no heat transfer), during this Stage, if m is
the mass of air in the buffer, C.sub.V and C.sub.P are the constant
volume and constant pressure specific heats, and T and V are the
air temperature and volume in the buffer, then
d(mC.sub.VT)=.multidot.pdV+C.sub.pTdm. But since p=p.sub.2 is
constant, pdV=d(p.sub.2V)=d(mRT) and C.sub.P-C.sub.V=R, where R is
the gas constant, this becomes d(mC.sub.pT)=C.sub.pTdm which shows
that T also is constant, T=T2 during Stage 3. With constant
temperature and pressure the air density also will remain constant,
.rho.=.rho..sub.2. 13 T 2 = T a ( L L - x 2 + x T2 ) - 1 ( 17 )
[0140] Then using the standard orifice equations, 14 - m . = C D A
o 2 ( p a p 2 ) 1 2 C p T 2 [ 1 - ( p a p 2 ) - 1 ] if p 2 p a ( +
1 2 ) - 1 or ( 18 ) - m . = C D A o 2 ( 2 + 1 ) 1 2 ( + 1 - 1 ) RT
2 if p 2 p a ( + 1 2 ) - 1 . ( 19 )
[0141] Using -{dot over (m)}=-.rho..sub.2{dot over
(V)}=.rho..sub.2A({dot over (x)}-{dot over (x)}.sub.T) and the
formulas above to get {dot over (x)}-{dot over (x)}.sub.T the
orifice area A.sub.0 can be calculated for any x-x.sub.T. Here
C.sub.D is the orifice coefficient, typically about 0.6. If
Equation (18) holds, then 15 A o = ( + 1 2 ) 1 2 ( + 1 - 1 ) A ( x
. - x . T ) C D RT 2 = ( + 1 2 ) 1 2 ( + 1 - 1 ) A ( x . 2 - x . T2
) C D RT 2 L - x + x T L - x 2 + x T2 ( 20 )
Motion of Truck
[0142] Equations (1) and (3) show that the increment in system
kinetic energy is 16 d ( W g x . 2 2 + W T g x . T 2 2 ) = W g x dx
+ W T g x ... T dx T = - A ( p - p a ) d ( x - x T ) - W T dx T = (
p - p a ) dV - W T dx T = - d ( mC V T ) + C p T 2 dm - p a dV - W
T dx T
[0143] The last form holds since dm is non-zero only when
T=T.sub.2. This equation can be integrated from the initial state
to the final state where both vehicles are at rest. Since the air
mass m in the final state is zero, the integral of d(mC.sub.VT) is
-m.sub.0C.sub.VT.sub.a, where m.sub.0 is the initial mass
p.sub.aAL/(RT.sub.a). The integral of C.sub.pT.sub.2dm is
-C.sub.pT.sub.2m.sub.0. The integral of P.sub.adV is -p.sub.aAL,
and the integral of .mu.W.sub.Tdx.sub.T is .mu.W.sub.TX.sub.T,
where X.sub.T is the total motion of the truck. When these are
substituted in and the relations C.sub.v+R=C.sub.p and
(.gamma..multidot.1)C.sub.p=.gamma.R are used, the equation can be
rearranged to yield 17 x T = 1 W T [ W g x . 2 2 - - 1 p a AL T 2 -
T a T a ] ( 21 )
Example
[0144] With the input W.sub.T=16000 lbs, W=4400 lbs, A=24 square
feet (3 feet by 8 feet), L=10 feet, {dot over (x)}.sub.0=62 mph,
.mu.=0.7, p.sub.a=14.7 psia, T.sub.a=68 F, C.sub.D=0.6,
.gamma.=1.4, R=1716.5 fps.sup.2 /R,
1 P+HD,1 = 17.94 psia Equation (9) X.sub.1 = 1.33 feet Equation
(10) {dot over (x)}.sub.1 = 61.6 mph Equation (11) x.sub.2 -
x.sub.T2 = 4.41 feet Equation (15) p.sub.2 = 33.2 psia Equation
(13) {dot over (x)}.sub.2 - {dot over (x)}.sub.T2 = 54.6 mph
Equation (14) T.sub.2 = 206 F Equation (17) A.sub.o,max = 4.37
square feet Equation (20) X.sub.T = 8.9 feet Equation (21)
* * * * *