Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to absorption of impact energ~
and more particularly to a resilient energy absorbing matrix
for vehicles having longitudinally e:~t~nding cells formed from
a lattic~ork of intersecting walls which taper from an inter-
mediate parting line to the outer and inner ends of the cells
to provide a new and improved energy management medium.
Prior to the present invention soft face energy
absorbers for vehicle application such as for front and rear
bumpers have been made from resilient plastic materials and
injection molded to have longitudinally extending cells. The
cells of these energy absorbers as usually installed are gen-
erally parallel to the longitudinal axis of the vehicle. On
impact of sufficient magnitude the walls of these cells twist
and buckle to absorb impact energy. on removal of the impact
load the cell walls gradually recover toward tlleir original
configuration, usually with no apparent damaga. Generally the
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cells of these prior energy absorbers have walls with a draft
angle which taper from a minimum thickness at one end of the
cells to a maximum thickness of the other end of the cells.
In cross-section, the walls of each cell have a wedge ox
triangle-like formation. This construction results from the
draft of the mold cores to facilitate ejection of the cellular
matrix from the mold. In such an energy absorbing construction
the thinner wall portion of the cells tend to deflect and knee-
over before the thick wall portions of the cell so that in most
impact situations only a limited portion of the impacted cells
are worked to absorb impact energy. Generally the thick wall
portions of the impacted cells remain undeflected and, there-
fore, ineffective for energy absorption.
In this invention the energy absorber is molded with
a split core mold, i.e., with mold cores extending from both
sides and meeting at a parting line, to provide a multicelled
energy absorbing matrix. The walls of the cells of this
matrix taper from a minimum thickness at either end thereof to
a maximized thickness at the parting line intermediate the ends
of the cells. The cross-sectional configuration of such walls
is generally diamond shaped so that longitudinally extending
inner and outer portions of each cell of the matrix as deter-
mined by the parting line form separate working zones which
buckle on impact. While the walls forming one zone may have a
thickness and draft angle different from the walls of the other
zone for tailoring the energy absorbing capability of the
matrix, it is generally the object of this invention to provide
a new and improved energy absorber with generally parallel open
cells which deflect from both ends on impact so that more
effective use is made of the energy absorbing abili~y of multi-
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1055~554
celled mediums. By appropriately changing the core heights
in the mold, the working zone depths of the cells can be
changed from equal to unequal zones to meet design and energy
management requirements. With the cells having walls which
progressively reduce in thickness from a maximized inter-
mediate thickness, a new and improved energy absorber cellu-
lar construction is provided which has reduced weight and
increased efficiency as compared to prior art multicelled
units. With the double tapered cellular walls, a new and
improved multicelled and molded energy absorbing unit is
provided which can be readily formed and easily removed from
the mold in a short cycle time. This invention provides for
saving in material and production costs. Additionally, this
invention provides for increased design flexibility with
added numbers of variable parameters such as having double
wall thicknesses, two draft angles and two core heights.
These and other features, objects and advantages of
this invention will be more apparent from the following
detailed description and drawing in which: ~ -
FIGURE 1 is a perspective view, with parts broken
away, of the preferred embodiment of this invention.
FIGURE 2 is an enlarged view of a portion of FIGURE
1. .
FIGURE 3 is a cross-sectional view taken along line
; 3-3 of FIGURE 2.
FIGURE 4 is a plot of force versus deflection
illustrating operation of this invention.
Turning now in greater detail to the drawing, there
is diagrammatically shown in FIGURE 1 a vehicle bumper assem-
bly 10 having a resilient energy absorbing matrix 12 formed
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from a suitable thermoplastic material such as a blencled
olefin. The matrix 12 has a plurality of longitudinally
extending and generally parallel cells 14 open throughout
their length which are formed by a latticework of inter-
secting horizontal and vertical]y extending walls 16 and
18. As best shown in FIGURES 2 and 3 the horizontal
and vertical walls 16 and 18 of the cells 14 taper from
a maximum thickness at a centralized split or dividing
line 20 intermediate the ends thereof to a minimized
thickness at their respective outer and inner ends. Thus,
horizontal walls 16 have a maximum thickness at split
line 20 and taper fr~ this line to a minimum thickness on
the outer and inner ends 24 and 26 respectively. Vertical
walls 18 have a maximum thickness at the split line 20
and taper from this line to a minimum thickness at their
respective inner and outer ends 28 and 30. With this
tapered construction, each cell will have outer and inner
deflecting zones Zl and Z2 illustrated best in FIGURE 3.
In the preferred embodiment of the invention shown in
FIGURE 1, the matrix 12 has an arcuate outer end surface
but this surface may be styled to have other configurations
as desired. Preferably, the inner and end surface of
matrix 12 is flat to seat against a substantially rigid
backing beam 32 which is suitable secured to the side rails
of a frame of a vehicle which is not shown. Additionally
any suitable fastener means may be employed to secure the
energy absorbing matrix to the bumper beam. For example,
some of the cells 14 can be modified and formed with
integral end walls for receiving fastener means such as
described in copending United States Patent No. 3,926,463
to DeWayne A. Landwehr et al for Energy Absorbing Cellular
Grid for Vehicles issued
1059S54
December 16, 1975. ~lso, to provide a finely finished
vehicle appearance a resilient plastic facia 36 may
be employed to cover the matrix as described in the
above-identified application. Attachment of the facia
to the vehicle body work and to the matrix 12, if
desired, can be any suitable fastener means.
In operation, assuming the energy absorbing unit
is impacted at a low vehicle speed, such as 5mph, the
inner and outer wall portions of the cells in the
impact area will simultaneously deflect to absorb im-
pact energy. With both inner and outer zones deflecting,
energy absorbing efficiency is improved as compared to
prior art units having cell walls that taper in thickness ;
progressively from one end to the other. This is illus-
trated in the force versus deflection plots of FIGURE 4.
Full line curve C represents the force deflection curve
of the cellular matrix of this inventioh and it will be -
seen that with both zines Zl and Z2 active the ideal square
wave force deflection curve D is approached. The energy
managed by resilient media is the work done in deforming
or compressing the media and, in the case of this invention
is represented by the area under curve C. This area is
larger than the area under dashed-line curve-E which
represents the force deflection of prior art cellular
energy absorbing media. Accordingly, there is increased
energy absorption potential with this invention with im-
proved efficiency as compared to conventional prior art
medai with longitudinally extending cells. After removal
of the impact load, the cell walls of this invention
gradually recover toward their original configuration so
that the facia is filled out and backed for subsequent
impact loads.
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If desired, the thickness of the Wall9 ~f the cells
14 could be varied to have two different wall thicknesses.
For example, the outer end 30 of the vertical walls 18 may
have a thickness greater than the corresponding thickness of
the inner end 28. With similar provisions being made for the
horizontal walls 16, it will be appreciated that the inner
zone Z2 will be of a thinner wall construction as compared to
outer zone Z~. With such an arrangement zone Z2 will buckle
and deflect at a diferent rate than the outer zone Zl
Accordingly, this construction provides new and improved means
for tailoring the matrix to absorb impact energy at predeter-
mined rates. If desired one zone such as Z2 could be thick
walled to have much greater resistance to deflection so that
zone Zl would buckle before any appreciable deflection in
zone Z2- Thus, a one-piece two-stage energy absorbing matrix
is provided for added protection in the event of high speed
impacts. While the split line 20 has been shown in the
center of the energy absorbing matrix, it can be readily
varied to be at any position inwardly or outwardly with respect
to the illustrated locationO This requires two different core
heights for each cell in forming the split line at other than
a central location. In any event tailoring and styling flexi- -
bility provided by the dual tapered cells provides increased
design potential. This lighter weight cellular construction
further improves molding cycle time since the cooiing period
after initial in~ection of heated material into the mold is
much shorter by virtue of the thinner outer and inner wall
portions of each cell.
While a preferred embodiment has been shown and
described for purposes of illustrating this invention, other
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embodiments embodying the concepts of this inVentiGn may be
adopted by thos~ skilled in the art, such as falls within
the scope of the appended claims.
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