U.S. patent application number 11/078848 was filed with the patent office on 2005-12-01 for customizable strut assemblies having variable stroke lengths and articles employing the same.
Invention is credited to Browne, Alan L., Johnson, Nancy L., Jones, Gary L., Mankame, Nilesh D., Stevenson, Robin, Ulicny, John C..
Application Number | 20050263359 11/078848 |
Document ID | / |
Family ID | 34994178 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050263359 |
Kind Code |
A1 |
Mankame, Nilesh D. ; et
al. |
December 1, 2005 |
Customizable strut assemblies having variable stroke lengths and
articles employing the same
Abstract
Disclosed herein is a strut assembly 10 comprising a housing 2;
a piston 3 in slideable communication with the housing 2; an
actuator 16 in operative communication with the piston 3 and/or the
housing 2; wherein the actuator 16 is adapted to change the
location of the housing 2 from a first position to a second
position and/or change in a stroke length of the piston 3.
Disclosed herein too is a method for changing the strut length of a
strut assembly 10 comprising activating an actuator 16 that is in
operative communication with a housing 2 or a piston of the strut
assembly 10; and changing in the location of the housing 2 from a
first position to a second position and/or changing a stroke length
of the piston 3.
Inventors: |
Mankame, Nilesh D.; (Ann
Arbor, MI) ; Stevenson, Robin; (Bloomfield, MI)
; Browne, Alan L.; (Grosse Pointe, MI) ; Johnson,
Nancy L.; (Northville, MI) ; Jones, Gary L.;
(Farmington Hills, MI) ; Ulicny, John C.; (Oxford,
MI) |
Correspondence
Address: |
Geneal Motors Corporation, Legal Staff
Mail Code 482-C23-B21
300 Renaissance Center
PO Box 300
Detroit
MI
48265
US
|
Family ID: |
34994178 |
Appl. No.: |
11/078848 |
Filed: |
March 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60552791 |
Mar 12, 2004 |
|
|
|
Current U.S.
Class: |
188/266.1 ;
188/266.2; 267/120; 267/124; 267/64.12 |
Current CPC
Class: |
F16F 9/46 20130101; F16F
9/56 20130101; F16F 9/368 20130101; E05B 2015/0493 20130101; F16F
9/54 20130101; E05B 51/005 20130101; F16F 9/466 20130101; Y10T
70/5093 20150401; F15B 21/065 20130101; F16F 2224/025 20130101;
F15B 15/204 20130101; Y10T 292/699 20150401; Y10T 292/17 20150401;
E05B 47/0009 20130101; E05B 47/0011 20130101; Y10T 292/1082
20150401; F16F 2224/0258 20130101; F15B 15/26 20130101; F16F
2224/045 20130101; F16F 15/005 20130101; E05B 81/20 20130101; F16F
2224/0283 20130101 |
Class at
Publication: |
188/266.1 ;
188/266.2; 267/120; 267/124; 267/064.12 |
International
Class: |
F16F 005/00 |
Claims
1. A strut assembly comprising: a housing; a piston in slideable
communication with the housing; an actuator in operative
communication with the piston and/or the housing; wherein the
actuator is adapted to change the location of the housing from a
first position to a second position and/or change in a stroke
length of the piston.
2. The strut assembly of claim 1, wherein the customizable strut
assembly is disposed between and in operative communication with a
suspended body and a supporting body, and wherein the actuator upon
actuation facilitates a change in the location of the suspended
body from a first position to a second position.
3. The strut assembly of claim 1, wherein the actuator comprises
one or more active elements 20 that comprise a shape memory
material, a passive material that does not have shape memory
properties, or a combination of the shape memory material and the
passive material.
4. The strut assembly of claim 1, wherein the actuator comprises
more than one active elements, and wherein the active elements are
disposed in series or parallel.
5. The strut assembly of claim 1, wherein the actuator is disposed
inside or outside the housing.
6. The strut assembly of claim 3, wherein the shape memory
materials comprise compositions that have the ability to remember
their original shape, and wherein the original shape can be
recalled by applying an external stimulus, and wherein the shape
memory materials are shape memory alloys, piezoelectrics,
electroactive polymers and/or piezoceramics.
7. The strut assembly of claim 1, wherein the actuator is an
electric stepper motor, an inchworm, a piezoelectric inchworm, an
ultrasonic motor, an electrohydrostatic actuator, a nanomotion
piezoelectric motor, a compact hybrid actuator device or
combinations thereof.
8. The strut assembly of claim 1, wherein the actuator is adapted
to change the stroke length of the piston or adapted to change in
the mean position of travel of the piston.
9. The strut assembly of claim 1, wherein the actuator is adapted
to change the stroke length of the piston while retaining the mean
position of travel of the piston.
10. The strut assembly of claim 1, wherein the actuator is located
outside the housing and is disposed between a supporting body and
the housing or between a suspended body and the piston.
11. The strut assembly of claim 1, wherein the actuator is located
inside the housing and is in operative communication with the
piston and/or within the housing.
12. The strut assembly of claim 11, wherein the actuator comprises
a coil spring manufactured from a shape memory alloy or wherein the
actuator comprises a block of a magnetorheological elastomer.
13. An article that employs the strut assembly of claim 1.
14. The article of claim 13, wherein the article comprises a door
on an automobile, aircraft, water craft or a residential building;
a hood or trunk of the automobile; a jaw of a vice or a press;
platens on machine tools; or arbors and chucks on machine
tools.
15. A method for changing the strut length of a strut assembly
comprising: activating an actuator that is in operative
communication with a housing or a piston of the strut assembly; and
changing in the location of the housing from a first position to a
second position and/or changing a stroke length of the piston.
16. The method of claim 15, wherein the activating of the actuator
occurs by the application of an external stimulus to a shape memory
material employed in the actuator, and wherein the external
stimulus can be an electrical stimulus, a magnetic stimulus, a
thermal stimulus, a chemical stimulus, a mechanical stimulus, an
ultrasonic stimulus or a combination comprising at least one of the
foregoing external stimuli.
17. The method of claim 15, wherein actuating the actuator
facilitates a change in the stroke length of the piston and a
change in the mean position of travel of the piston.
18. The method of claim 15, wherein actuating the actuator
facilitates a change in the stroke length of the piston while
retaining the mean position of travel of the piston.
19. The method of claim 15, wherein the actuator is located outside
the housing and wherein the actuator upon actuation displaces the
housing either towards the supporting body or away from the
supporting body.
20. An article employing the method of claim 15.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/552,791 filed Mar. 12, 2004, the entire
contents of which are hereby incorporated by reference.
BACKGROUND
[0002] This disclosure relates to strut assemblies whose stroke
lengths can be customized depending upon external conditions and
upon user preferences.
[0003] Strut assemblies are often used in automobiles to facilitate
the opening, locking and positioning of doors, trunks, hoods,
tail-gates, or the like. These assemblies have stroke lengths that
are fixed during the design, manufacturing or assembly process.
This can pose a problem for users of articles to which the strut
assembly is attached. For example, a tailgate lift having a large
stroke length can rise beyond the reach of smaller vehicle
users.
[0004] It is therefore desirable to use strut assemblies that offer
opportunities for customizing stroke length after the strut
assembly has been assembled or after the strut assembly has been
installed into an article such as a vehicle.
SUMMARY
[0005] Disclosed herein is a strut assembly comprising a housing; a
piston in slideable communication with the housing; an actuator in
operative communication with the piston and/or the housing; wherein
the actuator is adapted to change the location of the housing from
a first position to a second position and/or change in a stroke
length of the piston.
[0006] Disclosed herein too is a method for changing the strut
length of a strut assembly comprising activating an actuator that
is in operative communication with a housing or a piston of the
strut assembly; and changing in the location of the housing from a
first position to a second position and/or changing a stroke length
of the piston.
DETAILED DESCRIPTION OF FIGURES
[0007] FIG. 1 is a schematic depiction of a strut assembly 10
comprising a housing 2 that is in slideable communication with a
piston head 14 and a piston rod 12;
[0008] FIG. 2 is a schematic representation of an exemplary
embodiment of the improved customizable strut assembly 10 of this
disclosure wherein the assembly 10 comprises an actuator 16
disposed outside the housing 2;
[0009] FIG. 3 is a schematic representation of an exemplary
embodiment of the improved customizable strut assembly 10 wherein
the assembly 10 comprises an actuator 16 disposed inside the
housing 2;
[0010] FIG. 4 is a schematic representation of another exemplary
embodiment of the improved customizable strut assembly 10 wherein
the actuator 16 comprises an active element 20 manufactured from a
magnetorheological elastomer disposed inside the housing 2; and
[0011] FIG. 5 is a depiction of a schematic representation of strut
assembly 10 that comprises a sleeve 30 that is disposed upon the
outer surface of the housing 2. The sleeve 30 can be positioned
along the housing to adjust the effective stroke length. A
mechanical stop 34 can also be used to adjust the effective stroke
length.
DETAILED DESCRIPTION
[0012] Disclosed herein are strut assemblies whose stroke lengths
can be customized to provide the user with effective reach and
control over articles that are in operative communication with the
struts. The article may be any device that utilizes spatial
positioning such as a door in an automobile or a residential
building; the hood, trunk or tailgate of a automobile; the jaws of
a vice or a press; the platens on machine tools such as injection
molding machines, compression molding machines; arbors and chucks
on lathes and drilling machines, or the like.
[0013] The customizable strut assemblies disclosed herein differ
from those that are currently commercially available in that they
comprise active materials that permit some functional attributes of
the assemblies to be adjusted after manufacture. In one example, a
car owner can adjust the stroke length of the customizable strut
assembly to suit his or her anthropometrics. In another example, a
dealer can advantageously adjust the strut length of the strut
assembly at the point of sale to customize certain characteristics
of an otherwise mass produced vehicle to suit the desires of a
specific buyer. In another embodiment, an owner can adjust the
swing of an automobile door to prevent damage to the exterior of
surrounding vehicles when the owner has to park repeatedly in tight
parking spaces. In an exemplary embodiment, the stroke length can
be adjusted either via hardware tuning or via software changes.
[0014] With reference to the FIG. 1, which represents the prior
art, a strut assembly 10 comprises a housing 2 that is in slideable
communication with a piston 3. The piston 3 comprises a piston head
14 and a piston rod 12. The piston head 14 is fixedly attached to
the piston rod 12. The housing 2 contains a fluid 4. The piston
head 14 has disposed in it channels 8 that permit the passage of
fluid through the piston head 14 as it moves forward and backward
in the housing 2. Seals 6 are circumferentially disposed upon the
piston head 14 and seal the space between the piston head 14 and
the cylinder 2. Seals 6 can also be optionally disposed between the
piston rod 12 and the housing 2. The strut assembly 10 is in
operative communication with a supporting body 50 (e.g., the body
of the vehicle) and is also in operative communication with a
suspended body 60 (e.g., a panel that swings back and forth such as
a door). The supporting body 50 and the suspended body 60 are
disposed at opposing ends of the strut assembly 10.
[0015] While the FIG. 1 depicts the suspended body 60 as being
contacted by the housing 2 and the supporting body 50 as being
contacted by the piston rod 12, it is envisioned that the suspended
body 60 can be contacted by the piston rod 12 while the supporting
body can be contacted by the housing 2.
[0016] As the piston rod 12 slides back and forth in the housing 2
during the expansion or contraction of the strut assembly, the
fluid 4 is forced to flow through the channels 8 in the piston head
14. This flow is restricted by the channels 8 and the restricted
flow gives rise to two forces that resist relative motion between
the piston and the cylinder, an elastic force arising out of the
compression of the fluid column that the piston head is pushing
against, and a hydrodynamic force arising from the resistance to
fluid flow through the channels 8 in the piston head 14. Friction
brought on by the presence of the seal 6 between the piston head 14
and the inner wall of the housing 2, or between the piston rod 12
and the housing 2, also resists relative motion between the piston
head and the cylinder.
[0017] As the geometries of the different elements of the strut
assembly displayed in the FIG. 1 are fixed at the time of design
and manufacture of the strut assembly 10, there is no opportunity
to vary the strut stroke-length to suit varying anthropometrics of
the consumer. For example, the swing of a car door that employs the
strut assembly of FIG. 1 cannot be increased to accommodate a very
large person entering or exiting the car. Similarly, the swing of
the door cannot be decreased to prevent the door from opening
beyond the reach of a small person.
[0018] By being able to vary the stroke length of the strut
assembly 10, the distance between the suspended body 60 and the
supporting body 50 can be adjusted accordingly as desired. The
stroke length is generally varied by the inclusion of an actuator
in the strut assembly. The actuator may be disposed within the
housing or external to the housing. The actuator generally
comprises an active element that comprises a shape memory material
(active material). The actuator can comprise one or more active
elements that can be arranged in series or in parallel inside or
outside the housing.
[0019] The actuator can be in operative communication with either
the housing and/or the piston. In one embodiment, the actuator can
cause a change in the stroke length of the strut assembly by
changing the distance between the supporting body and the suspended
body. This is accomplished by changing the location of the housing
with respect to the supporting body and/or the suspended body. By
changing the location of the housing from a first position to a
second position, the supporting body is correspondingly moved from
its first position to a second position. This change in the strut
length brought on by changing the location of the housing can be
manually controlled and effected or it can be computer
controlled.
[0020] In another embodiment, the actuator can cause a change in
the strut length of the strut assembly by changing the effective
stroke length of the piston. Activating the actuator changes the
length of travel of the piston in the housing. In one embodiment,
upon changing the length of travel of the piston in the housing,
the mean position of travel of the piston is changed. The mean
position of travel of the piston is the location of mid-point of
travel of the piston in the housing. For example, f the piston
travels back and forth between points A and B in the housing (i.e.,
A and B represents the extremities of travel of the piston) then
the mean position of travel will be the sum of A and B divided by
2. Thus in one embodiment, upon actuating the actuator, the length
of travel can be changed, while the mean position of travel remains
the same. In another embodiment, the length of travel of the piston
is changed while the mean position of travel is also changed. This
change in the strut length brought on by changing the effective
length of travel of the piston, which can be manually controlled
and effected or it can be computer controlled.
[0021] With reference now to the FIG. 2, which represents an
embodiment of the improved customizable strut assembly 10 of this
disclosure, the assembly 10 comprises an actuator 16 interposed
between the suspended body 60 and the housing 2. The actuator 16 is
in operative communication with the housing 2 and the suspended
body 60. The actuator 16 comprises one or more active elements 20
that can be adjusted to effectively increase the stroke length in a
direction parallel to the direction of travel of the piston rod 12.
The actuator 16 may be used to assist the displacement of the
suspended body 60 away from and/or towards the supporting body 50
depending upon the desires of the user. As noted above, the
actuator 16 can be in operative communication with the housing 2 or
the piston rod 12.
[0022] In one embodiment, a suitable example of actuators 16 that
employ active elements 20 that comprise active materials are
electric stepper motors, inchworms, piezoelectric inchworms,
ultrasonic motors, electrohydrostatic actuators, nanomotion
piezoelectric motors, compact hybrid actuator devices (CHAD), that
may be employed in the actuator 16. These motors can be used in the
customizable strut assemblies 10 external to the housing 2 as
depicted in the FIG. 2 and can facilitate a change in distance
between the suspended body 60 and the supporting body 50. In
another embodiment, the active element 20 can involve a coil
spring, a wire or other geometrical shape manufactured from an
active material that can facilitate a change in distance between
the suspended body 60 and the supporting body 50.
[0023] Shape memory materials generally refer to materials or
compositions that have the ability to revert to a specified
configuration (e.g. crystal structure, shape, or the like) in
response to suitable external stimuli, e.g., an activation signal.
Exemplary shape memory materials suitable for use in the present
disclosure include shape memory alloys, ferromagnetic shape memory
alloys, shape memory polymers and composites of the foregoing shape
memory materials with non-shape memory materials, and combinations
comprising at least one of the foregoing shape memory materials. In
another embodiment, the class of active materials used in the
customizable strut assembly 10 are those that change their shape in
proportion to the strength of the applied field but then return to
their original shape upon the discontinuation of the field.
Exemplary active materials in this category are electroactive
polymers (dielectric polymers), piezoelectrics, and piezoceramics.
Activation signals can employ an electrical stimulus, a magnetic
stimulus, a chemical stimulus, a mechanical stimulus, a thermal
stimulus, or a combination comprising at least one of the foregoing
stimuli. In one embodiment, the return to the original shape is
accomplished by the use of a restoring force such as, for example,
a biasing spring. Exemplary materials that can employ a restoring
force are shape memory alloys.
[0024] For convenience and by way of example, reference herein will
be made to shape memory alloys. Shape memory alloys (SMA's)
generally refer to a group of metallic materials that demonstrate
the ability to return to some previously defined shape or size when
subjected to an appropriate thermal stimulus. Shape memory alloys
are capable of undergoing phase transitions in which their elastic
modulus, yield strength, and shape orientation are altered as a
function of temperature. Generally, in the low temperature, or
martensite phase, shape memory alloys can be plastically deformed
and upon exposure to a specified higher temperature will transform
to an austenite phase, or parent phase, attempting to return to
their shape prior to the deformation. Materials that exhibit this
shape memory effect only upon heating are referred to as having
one-way shape memory. Those materials that also exhibit shape
memory upon re-cooling are referred to as having two-way shape
memory behavior.
[0025] Shape memory alloys can exhibit a one-way shape memory
effect, an intrinsic two-way effect, or an extrinsic two-way shape
memory. Annealed shape memory alloys generally exhibit the one-way
shape memory effect. Sufficient heating subsequent to
low-temperature deformation of the shape memory material will
induce the martensite to austenite type transition, and the
material will recover the original, annealed shape. Hence, one-way
shape memory effects are only observed upon heating.
[0026] Intrinsic two-way shape memory alloys are characterized by a
shape transition both upon heating from the martensite phase to the
austenite phase, as well as an additional shape transition upon
cooling from the austenite phase back to the martensite phase. In
contrast, active connector elements that exhibit the extrinsic
two-way shape memory effects are composite or multi-component
materials that combine a shape memory alloy composition that
exhibits a one-way effect with another element that provides a
restoring force to return the first plate another position or to
its original position. Active elements that exhibit an intrinsic
one-way shape memory effect are fabricated from a shape memory
alloy composition that will cause the active elements to
automatically reform themselves as a result of the above noted
phase transformations. Intrinsic two-way shape memory behavior must
be induced in the shape memory material through thermo-mechanical
processing. Such procedures include extreme deformation of the
material while in the martensite phase, heating-cooling under
constraint or load, or surface modification such as laser
annealing, polishing, or shot-peening. Once the material has been
trained to exhibit the two-way shape memory effect, the shape
change between the low and high temperature states is generally
reversible and persists through a high number of thermal
cycles.
[0027] The temperature at which the shape memory alloy remembers
its high temperature form when heated can be adjusted by slight
changes in the composition of the alloy and through heat treatment.
In nickel-titanium shape memory alloys, for instance, it can be
changed from above about 100.degree. C. to below about -100.degree.
C. The shape recovery process occurs over a range ofjust a few
degrees and the start or finish of the transformation can be
controlled to within a few degrees depending on the alloy
composition.
[0028] Suitable shape memory alloy materials for fabricating the
active elements include nickel-titanium based alloys,
indium-titanium based alloys, nickel-aluminum based alloys,
nickel-gallium based alloys, copper based alloys (e.g., copper-zinc
alloys, copper-aluminum alloys, copper-gold, and copper-tin
alloys), gold-cadmium based alloys, silver-cadmium based alloys,
indium-cadmium based alloys, manganese-copper based alloys,
iron-platinum based alloys, iron-palladium based alloys, or the
like, or a combination comprising at least one of the foregoing
shape memory alloys. The alloys can be binary, ternary, or any
higher order so long as the alloy composition exhibits a shape
memory effect, e.g., change in shape orientation, changes in yield
strength, and/or flexural modulus properties, damping capacity, and
the like.
[0029] The thermal activation signal may be applied to the shape
memory alloy in various ways. It is generally desirable for the
thermal activation signal to promote a change in the temperature of
the shape memory alloy to a temperature greater than or equal to
its austenitic transition temperature. Suitable examples of such
thermal activation signals that can promote a change in temperature
are the use of steam, hot oil, resistive electrical heating, or the
like, or a combination comprising at least one of the foregoing
signals. A preferred thermal activation signal is one derived from
resistive electrical heating.
[0030] The active element 20 may also be an electrically active
polymer. Electrically active polymers are also commonly known as
electroactive polymers (EAP's). The key design feature of devices
based on these materials is the use of compliant electrodes that
enable polymer films to expand or contract in the in-plane
directions in response to applied electric fields or mechanical
stresses. When electroactive polymers are used as the active
element 20, strains of greater than or equal to about 100%,
pressures greater than or equal to about 50 kilograms/square
centimeter (kg/cm.sup.2) can be developed in response to an applied
voltage. The good electromechanical response of these materials, as
well as other characteristics such as good environmental tolerance
and long-term durability, make them suitable for use in active
elements under a variety of manufacturing conditions. Electroactive
polymers are suitable for use as an active element in many
customizable strut assembly 10 configurations.
[0031] Electroactive polymer actuator elements used in customizable
strut assembly 10 may be selected based on one or more material
properties such as a high electrical breakdown strength, a low
modulus of elasticity-(for small deformations), a high dielectric
constant, and the like. In one embodiment, a polymer is selected
such that is has an elastic modulus at most about 100 MPa. In
another embodiment, the polymer is selected such that is has a
maximum actuation pressure between about 0.05 MPa and about 10 MPa,
and preferably between about 0.3 MPa and about 3 MPa. In another
embodiment, the polymer is selected such that is has a dielectric
constant between about 2 and about 20, and preferably between about
2.5 and about 12. The present disclosure is not intended to be
limited to these ranges. Ideally, materials with a higher
dielectric constant than the ranges given above would be desirable
if the materials had both a high dielectric constant and a high
dielectric strength. In many cases, electroactive polymers may be
fabricated and implemented as thin films. Thicknesses suitable for
these thin films may be below 50 micrometers.
[0032] As electroactive polymers may deflect at high strains,
electrodes attached to the polymers should also deflect without
compromising mechanical or electrical performance. Generally,
electrodes suitable for use may be of any shape and material
provided that they are able to supply a suitable voltage to, or
receive a suitable voltage from, an Electroactive polymer. The
voltage may be either constant or varying over time. In one
embodiment, the electrodes adhere to a surface of the polymer.
Electrodes adhering to the polymer are preferably compliant and
conform to the changing shape of the polymer. Correspondingly, the
present disclosure may include compliant electrodes that conform to
the shape of an electroactive polymer to which they are attached.
The electrodes may be only applied to a portion of an electroactive
polymer and define an active area according to their geometry.
Various types of electrodes suitable for use with the present
disclosure include structured electrodes comprising metal traces
and charge distribution layers, textured electrodes comprising
varying out of plane dimensions, conductive greases such as carbon
greases or silver greases, colloidal suspensions, high aspect ratio
conductive materials such as carbon fibrils and carbon nanotubes,
and mixtures of ionically conductive materials.
[0033] Materials used for electrodes may vary. Suitable materials
used in an electrode may include graphite, carbon black, colloidal
suspensions, thin metals including silver and gold, silver filled
and carbon filled gels and polymers, and ionically or
electronically conductive polymers. It is understood that certain
electrode materials may work well with particular polymers and may
not work as well for others. By way of example, carbon fibrils work
well with acrylic elastomer polymers while not as well with
silicone polymers.
[0034] The electroactive polymers used herein are generally
conjugated polymers. Suitable examples of electroactive polymers
are poly(aniline), substituted poly(aniline)s, polycarbazoles,
substituted polycarbazoles, polyindoles, poly(pyrrole)s,
substituted poly(pyrrole)s, poly(thiophene)s, substituted
poly(thiophene)s, poly(acetylene)s, poly(ethylene dioxythiophene)s,
poly(ethylenedioxypyrrole)s, poly(p-phenylene vinylene)s, or the
like, or combinations comprising at least one of the foregoing
electroactive polymers. Blends or copolymers or composites of the
foregoing electroactive polymers may also be used. Similarly blends
or copolymers or composites of an electroactive polymers with an
electroactive polymers precursor may also be used.
[0035] The actuator element 20 used in the customizable strut
assembly 10 may also comprise a piezoelectric material. Also, in
certain embodiments, the piezoelectric material may be configured
for providing rapid deployment. As used herein, the term
"piezoelectric" is used to describe a material that mechanically
deforms (changes shape and/or size) when a voltage potential is
applied, or conversely, generates an electrical charge when
mechanically deformed. As piezoelectric actuators have a small
output stroke, they are usually coupled with a transmission (e.g. a
compliant mechanism) that serves to amplify the output stroke at
the expense of a reduction in the output force. As an example, a
piezoelectric material is disposed on strips of a flexible metal
sheet. The piezo actuators are coupled to the sheet in a manner
that causes bending or unbending of the sheet when the actuators
are activated. The ability of the bending mode of deformation in a
flexible shell to amplify small axial strains into larger rotary
displacements is used to advantage. The strips can be unimorph or
bimorph. Preferably, the strips are bimorph, because bimorphs
generally exhibit more displacement than unimorphs.
[0036] In contrast to the unimorph piezoelectric device, a bimorph
device includes an intermediate flexible metal foil sandwiched
between two piezoelectric elements. Bimorphs exhibit more
displacement than unimorphs because under the applied voltage one
ceramic element will contract while the other expands. Bimorphs can
exhibit strains up to about 20%, but similar to unimorphs,
generally cannot sustain high loads relative to the overall
dimensions of the unimorph structure.
[0037] Suitable piezoelectric materials include inorganic
compounds, organic compounds, and metals. With regard to organic
materials, all of the polymeric materials with non-centrosymmetric
structure and large dipole moment group(s) on the main chain or on
the side-chain, or on both chains within the molecules, can be used
as candidates for the piezoelectric film. Examples of suitable
polymers include, for example, but are not limited to, poly(sodium
4-styrenesulfonate) ("PSS"), poly S-119 (poly(vinylamine) backbone
azo chromophore), and their derivatives; polyfluorocarbons,
including polyvinylidene fluoride ("PVDF"), its co-polymer
vinylidene fluoride ("VDF"), trifluoroethylene (TrFE), and their
derivatives; polychlorocarbons, including poly(vinyl chloride)
("PVC"), polyvinylidene chloride ("PVC2"), and their derivatives;
polyacrylonitriles ("PAN"), and their derivatives; polycarboxylic
acids, including poly(methacrylic acid ("PMA"), and their
derivatives; polyureas, and their derivatives; polyurethanes
("PUE"), and their derivatives; bio-polymer molecules such as
poly-L-lactic acids and their derivatives, and membrane proteins,
as well as phosphate bio-molecules; polyanilines and their
derivatives, and all of the derivatives of tetramines; polyimides,
polyetherimides ("PEI"), and their derivatives; all of the membrane
polymers; poly(N-vinyl pyrrolidone) ("PVP") homopolymer, and its
derivatives, and random PVP-co-vinyl acetate ("PVAc") copolymers;
and all of the aromatic polymers with dipole moment groups in the
main-chain or side-chains, or in both the main-chain and the
side-chains, and mixtures thereof.
[0038] Further, piezoelectric materials can include Pt, Pd, Ni, Ti,
Cr, Fe, Ag, Au, Cu, and metal alloys and mixtures thereof. These
piezoelectric materials can also include, for example, metal oxide
such as SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2,
SrTiO.sub.3, PbTiO.sub.3, BaTiO.sub.3, FeO.sub.3, Fe.sub.3O.sub.4,
ZnO, and mixtures thereof; and Group VIA and IIB compounds, such as
CdSe, CdS, GaAs, AgCaSe 2, ZnSe, GaP, InP, ZnS, and mixtures
thereof.
[0039] The active element 20 can also comprise magnetorheological
(MRE) elastomers. Magnetorheological elastomers (MRE) are
suspensions of micrometer-sized, magnetically polarizable particles
in a polymeric elastomer. When a magnetorheological elastomer is
exposed to a magnetic field, the normally randomly oriented
particles form chains of particles in the direction of the magnetic
field lines. The particle chains increase the effective stiffness
of the elastomer. The change in the effective stiffness of the MRE
is accomplished by changing the shear and compression/tension
modulii of the magnetorheological elastomer by varying the strength
of the applied magnetic field. The magnetorheological elastomers
typically develop structure when exposed to a magnetic field in as
little as a few milliseconds. Discontinuing the exposure of the
magnetorheological elastomer to the magnetic field reverses the
process and the elastomer returns to a lower viscosity state.
[0040] Suitable magnetorheological elastomer materials include an
elastic polymer matrix comprising a suspension of ferromagnetic or
paramagnetic particles, wherein the particles are described above.
Suitable polymer matrices include poly-alpha-olefins, copolymers of
poly-alpha-olefins and natural rubber.
[0041] Suitable ferromagnetic or paramagnetic include iron; iron
alloys, such as those including aluminum, silicon, cobalt, nickel,
vanadium, molybdenum, chromium, tungsten, manganese and/or copper;
iron oxides, including Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4; iron
nitride; iron carbide; carbonyl iron; nickel and alloys of nickel;
cobalt and alloys of cobalt; chromium dioxide; stainless steel;
silicon steel; or the like, or a combination comprising at least
one of the foregoing particles. Examples of suitable iron particles
include straight iron powders, reduced iron powders, iron oxide
powder/straight iron powder mixtures and iron oxide powder/reduced
iron powder mixtures. A preferred magnetic-responsive particulate
is carbonyl iron, preferably, reduced carbonyl iron.
[0042] The particle size should be selected so that the particles
exhibit multi-domain characteristics when subjected to a magnetic
field. Diameter sizes for the particles can be less than or equal
to about 1,000 micrometers, with less than or equal to about 500
micrometers preferred, and less than or equal to about 100
micrometers more preferred. Also preferred is a particle diameter
of greater than or equal to about 0.1 micrometer, with greater than
or equal to about 0.5 more preferred, and greater than or equal to
about 10 micrometer especially preferred. The particles are
preferably present in an amount between about 5.0 and about 50
percent by volume of the total composition.
[0043] With reference now again to the FIG. 2, in one embodiment,
in one manner of operating the customizable strut assembly 10 in
order to vary its stroke length, an external stimulus is applied to
the active element 20. A preferred external stimulus is one derived
from thermal activation preferably one that is derived from
resistive electrical heating. As described earlier, the active
element 20 can be a composite of SMP, an elastic material and one
or more active material based actuators (e.g. SMA or EAP); or a
composite of SMP and an elastic material; or a sub-assembly
comprising one or more active material based actuators that are
mechanically coupled to elastic restoring elements; etc. In each
case, the overall axial dimension of the active element can be
changed in response to the activation signal to achieve the desired
strut stroke adjustment. This change in length facilitates the
displacement of the suspended body 60 with respect to the
supporting body 50, thereby changing the effective stroke length of
the customizable strut assembly 10. The magnitude of the change in
length can be proportioned to the magnitude of the activation
signal.
[0044] FIGS. 3 and 4 depict exemplary embodiments of customizable
strut assemblies that utilize active elements that are disposed
inside the housing 2. With reference now to the FIG. 3, the
customizable strut assembly 10 comprises plates 22 that are in
operative communication with the active element 20. The plates are
perforated to allow easy passage for the fluid. The plates 22 and
the active element 20 are disposed within the housing 2. The active
element 20 for purposed of this embodiment is a coil spring, though
it can be varied in shape and size in other configurations. The
plates 22 are disposed on opposing sides of the piston head 14 and
are in operative communication with the piston head 14. The
perforations in the plate 22 allow for a smooth displacement of the
fluid 4 within the housing 2 as the piston 3 slides back and forth
in the housing 2.
[0045] In the prior art strut assembly (e.g., as shown in FIG. 1),
the ends of the strut stroke are marked by (near) contact between
the flat ends of the piston head and the respective cylinder ends.
In the adjustable strut assembly shown in the FIGS. 3 and 4, the
end of stroke is marked by contact between the elements 22 and the
respective ends of the cylinder. Therefore, it is clear that by
changing the axial length and/or the stiffness of the active
elements 20, the effective stroke of the strut can be adjusted.
[0046] In one embodiment, the active element 20 can be a composite
of a shape memory polymer, an elastic material and one or more
active material based actuators (e.g., a shape memory alloy or and
electroactive polymer); or a composite of shape memory polymer and
an elastic material; or a sub-assembly comprising one or more
active material based actuators that are mechanically coupled to
elastic restoring elements; or the like. In each case, the overall
axial dimension of the actuator can be changed in response to the
activation signal to achieve the desired strut stroke adjustment.
Depending on the active materials and the configuration in which
they are used, the change in the stroke may stay in effect until it
is changed again, or the change may be made just-in-time for an
operation and will remain in effect only for that operation. In
another embodiment, the active element 20 comprises a spring made
of a shape memory alloy in its martensitic-phase over the operating
temperature range for the strut.
[0047] As noted above, the actuator 16 generally comprises an
active element 20 that comprises an active material. An active
material generally refers to a group of materials that demonstrate
an ability to return to some previously defined shape or size when
subjected to an appropriate external stimulus. The active material,
upon activation facilitates the displacement of the suspended body
60 towards and/or away from the supporting body 50 and also permits
control over the magnitude of the displacement.
[0048] In another embodiment, the actuator 16 can also comprise a
composite of an active material. In one embodiment, the composite
can comprise a shape memory alloy and a shape memory polymer. In
another embodiment, the composite can comprise a shape memory alloy
and a material that is not an active material, i.e., a material
that does not return to some previously defined shape or size when
subjected to an appropriate external stimulus. In yet another
embodiment, the composite can comprise two or more active materials
such as for example a shape memory alloy and a shape memory polymer
in addition to and a material that is not an active material.
[0049] For example, an actuator can comprise a composite that
comprises one or more elastic elements made from spring steel
distributed within a shape memory polymer matrix together with one
or more shape memory alloy elements. The shape memory polymer has a
characteristic temperature known as its glass transition
temperature (Tg), such that the elastic modulus of the material
drops significantly e.g., a factor of about 30 to about 150 when it
is heated above its Tg. The shape memory polymer is a soft and
easily pliable polymer above the Tg, and it can be deformed
significantly (up to 200% recoverable strain) by a relatively low
force. On cooling the deformed shape memory polymer below its Tg,
the material reverts back to its stiffer form, while retaining the
deformed shape in a stress-free condition. If a specified limiting
temperature is not exceeded during the heating process, the
aforementioned procedure comprising heating, deforming and cooling
can be repeated multiple times.
[0050] The elastic elements in the above embodiment are
mechanically coupled to the shape memory polymer matrix and, they
determine the overall configuration (i.e. geometry, dimensions,
etc) of the active element. The relative stiffnesses of the elastic
elements and the shape memory polymer matrix are chosen such that,
when the shape memory polymer is below the lower Tg, it is the
dominant contributor to the overall stiffness of the actuator;
whereas when the shape memory polymer is above the Tg, the elastic
elements are the dominant contributors to the overall active
element stiffness. Depending on the manner in which the shape
memory elements are activated, they can either compress or elongate
the elastic elements and thereby, control the overall configuration
of the active element when the shape memory polymer is above the
Tg.
[0051] The use of the actuator can be illustrated by describing the
process in which the actuator is reconfigured to tailor the
strut-stroke. The shape memory polymer is softened by heating it to
a temperature above its Tg. The shape memory alloy elements are
then activated to change the overall configuration of the actuator
while the shape memory polymer is soft. Once the actuator achieves
the desired configuration (e.g. axial dimension), the shape memory
polymer is allowed to cool down to a temperature below its Tg,
whereupon it regains its stiff form. The shape memory alloy
elements are then powered off. As described earlier, the stiffness
of the shape memory polymer matrix dominates that of the elastic
elements, and hence the active element will retain the above
configuration until it is heated above its Tg. The above
reconfiguration process can then be repeated.
[0052] As the piston 3 slides within the housing 2, the active
elements 20 are compressed at one or both ends of the strut's
stroke. If the stiffness of these active elements 20 is small,
e.g., when the shape memory alloy is in its martensitic phase, they
can be easily compressed between the piston 3 and the housing 2.
Hence, they will not affect the length of the stroke. However, if
the stiffness of the active elements is high, e.g., when the shape
memory alloy is in its austenitic phase, they resist relative
motion between the piston 2 and the housing 2 with considerable
force at the extremities of the strut's stroke. The amount of
change in the stroke length is directly proportional to the length
of the active element 20 and its stiffness. Thus a stiffening of
the active element 20 upon activation will result in a reduction of
the effective stroke length for the customizable strut assembly
10.
[0053] In one embodiment, by activating the active element 20, the
length of the active element 20 can be varied, thereby varying the
length of travel of the piston 3 in the housing 2. This will alter
the stroke length of the strut assembly 10. The activation signal
can be a thermal signal brought on by resistive heating of the
spring. Depending on the range of stroke variation required,
similar plates can also be connected to one or both ends of the
housing 2 through active elements 20, whose lengths and/or
stiffnesses can be varied upon activation.
[0054] In addition to changing the stroke of the strut assembly 10,
varying the stiffness of the various active elements in the strut
assembly can enable control over which part of the stroke is
curtailed (e.g., the tailgate lift needs to be reduced for shorter
owners; the tailgate may need to be held partially open when
transporting over size cargo that extends partially out of the
vehicle, in which case the tailgate closure needs to be
restricted), and afford smoother operation of the customizable
strut assembly 10.
[0055] When the active element 20 in the FIG. 3 is a coil spring
made from a shape memory alloy material, the customizable strut
assembly can be modified to function in various modes. In one mode,
when the spring is in its martensitic phase over the temperature
range of operation of the customizable strut assembly 10, it has a
low stiffness and hence a low spring constant than when it is in
the austenitic form. Passage of an electric current through the
spring can induce a martensitic to austenitic transition in the
spring material, thereby increasing its stiffness e.g. three-fold.
The dual-stiffness nature of the SMA spring can be used to vary the
stroke of the strut as described above. Depending on the
composition of the shape memory alloy material, the transition from
soft to stiff can be sharp or gradual, thereby yielding greater
control over the behavior of the strut at the extremities of its
stroke.
[0056] In yet another embodiment, depicted in the FIG. 4,
magnetorheological elastomers can be employed as the active element
20. In this embodiment, the piston 3 comprises an electromagnet 26
that is in mechanical and electrical communication with the
magnetorheological elastomer of the active element 20. The
magnetorheological elastomer is in the form of a block that is
disposed on opposing surfaces of the piston head 14. The active
element 20 has a size effective to vary the length of the stroke as
its stiffness is increased. When an electrical current is passed
through the electromagnet 26, a magnetic field is set up inside the
magnetorheological elastomer. Since the stiffness of the
magnetorheological elastomer can be varied by varying the strength
of the magnetic field, the change in stiffness can be controlled by
varying the electrical current passing through the electromagnet.
By changing the stiffness of the magnetorheological elastomer, the
length of the stroke can be varied in a manner that is conceptually
similar to that described above in the context of SMA springs. As
the elastomer becomes less stiff, it can be easily compressed
between the piston 3 and the inner surface of the housing 2,
thereby permitting a larger stroke length. As the electrical
current is varied to increase the stiffness of the elastomer, it
cannot be easily deformed between the piston 3 and the inner
surface of the housing 2. Thus by varying the magnitude of the
activation signal to the active element 20, the length of travel of
the customizable strut assembly 10 can be adjusted. The use of a
biasing permanent magnet, whose influence on the MRE can be
counteracted by an electromagnet allows this concept to be extended
to both: increase and decrease the effective strut stroke.
[0057] In yet another exemplary embodiment, depicted in the FIG. 5,
the strut assembly 10 comprises a sleeve 30 that is disposed upon
the outer surface of the housing 2. The sleeve 30 is hollow and
comprises a braking mechanism 32 that fixedly attaches it to the
housing 2 depending upon the user's preference. The sleeve 30 can
have any suitable cross-sectional geometry that permits slideable
motion with the housing 2, when the braking mechanism 32 is
released. The braking mechanism is generally released when it is
desirable to change the effective length of the strut assembly 10
after which it is reengaged to fixedly attach the sleeve 32 to the
housing 2. The braking mechanism 32 can be engaged or disengaged by
a suitable stimulus to change the effective length of the strut
assembly. Adjusting the position of the sleeve 32 controls the
distance labeled DS2.
[0058] A mechanical stop 34 is fixedly attached to the piston rod
12 at the user's discretion and can be used to adjust the effective
stroke length by displacing the mechanical stop when desired. The
location of the mechanical stop 34 determines the distance DS1 as
shown in the FIG. 5. The mechanical stop 34 can be adjusted upon
temporary removal of the sleeve 30. When the braking mechanism 32
is disengaged, the sleeve 30 can be freely positioned at any
desirable point over the length of the housing 2 subject to
mechanical interference constraints imposed by the cylinder
dimensions. When the braking mechanism 32 is engaged and the sleeve
30 is mechanically coupled to the housing 2, the effective-length
of the strut assembly is controlled by the larger of the two
distances, DS1 and DS2.
[0059] Once the position of the mechanical stop 34 is fixed
relative to the piston rod 12, the motion of the suspended body 60
is governed by the smaller of the two distances DO1 and DO2 as
shown in the FIG. 5. These correspond to mechanical interference
between the piston 3 and the end of the cylinder proximate to the
supporting body 50, and between the end of the cylinder proximate
to the supporting body 50 and the mechanical stop 34. Changing the
position of the mechanical stop 34 allows the length DO2 to be
adjusted. This affords control over the motion of the suspended
body 60 when it is to be opened completely.
[0060] In an alternative embodiment, the position of the mechanical
stop 34 can be adjusted using an optional biasing spring 36 as
depicted in the FIG. 5. The bias spring can be of a length
effective to keep the mechanical stop in communication with the end
of the sleeve 30 proximate to the supporting body 50. The spring
force (i.e., the spring constant) is negligible compared to the
braking resistance produced when the mechanical stop 32 is engaged.
Therefore, the spring 36 does not affect the position of the
mechanical stop 32, when the brake is engaged. In one embodiment,
in one method of determining the fully open position of the
suspended body 60, the mechanical stop 34 is disengaged and the
braking mechanism 32 is engaged thereby permitting the swing panel
to be displaced into the desired fully-open position. At this point
the mechanical stop 34 is engaged locking in the range of desired
motion for the strut assembly 10. The sleeve 30 moves with the
suspended body 60 during its motion and the mechanical stop 34
moves with the spring 36 to its new location.
[0061] The desired fully-shut position can be set in a similar way.
Here the braking mechanism 32 is disengaged and the suspended body
60 is moved to the desired fully-shut position before the braking
mechanism 32 is engaged again. The piston rod 3 can be used to
displace the sleeve 30 to the desired position. Again, a soft bias
spring (not shown) can be used to keep the sleeve 30 flush against
the end of the piston rod that is proximate to the supporting body
50.
[0062] The ability to customize the length of travel of a
customizable strut assembly 10 can be advantageously used in
automobiles, aircraft, ships, in machine tools, or the like, to
improve usability. The length of travel can be adjusted at any time
during the life cycle of an article that employs the customizable
strut assembly. The length of travel can also be adjusted to
accommodate ambient weather conditions, consumer anthropometrics or
to offset the deleterious effects of component wear. The length of
travel can be adjusted manually or by computer as desired.
[0063] While the disclosure has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *