Patent Application
20160076294
This invention pertains to self-adjusting panel closure bumpers, passive supports for vehicle sheet metal closure panels, and methods of use.
In discussion of motor vehicle construction, a distinction is commonly made between the frame structure of the vehicle body, in which sheet metal components are welded or bolted together and maintained in fixed and permanent relation to one another, and closure panels which are designed and intended to open and close to permit access to the interior of the frame structure. Examples of such closure panels include doors, hoods, hatches, and decklids, each of which is commonly attached to the body via spaced apart hinges at, or near, one edge and straddling a panel centerline. Closure panels also commonly incorporate a locking and latching mechanism, mounted on or near the edge of the closure panel opposite the hinges, and usually positioned on the same panel centerline.
Each closure panel typically comprises two attached sheet metal stampings. The first stamping, usually called an outer panel is viewable by an external observer. The second stamping usually called an inner panel is normally hidden from view. The inner and outer panels may be attached at both their edges and interior locations, such as hoods and decklids, or secured only at their edges with a hollow space between inner and outer panels to accommodate, for example, a window and its operating mechanism, or a loudspeaker, or various electrical or electronic switches and controls. Commonly such construction is found in doors and hatches.
Closure panels are intended to fit centrally within a corresponding opening within the vehicle body so that a uniform and consistent gap is maintained between the edge of the closure and the body opening. The positioning of the closure panels within the body opening is established by the cooperative interaction of the hinges and the locking structure. These also contribute to ensuring that the panel is maintained at its correct elevation relative to the adjacent panels so that there is continuity of line between the body and the closure panel without dips, rises, and/or tilts which would be displeasing to an observer. Supplementary supports to control closure panel elevation are often used. These supports, more properly called panel closure bumpers, or simply, bumpers are typically, but not necessarily, mounted to the vehicle body, and extend outwardly from the body a suitable distance to contact and support the closure panel.
In addition, the bumpers serve to control flex, vibration, and noise which may occur during closing of the panel. In closing, such panels are commonly rotated under acceleration to ensure full engagement of the lock with the locking mechanism. This sudden deceleration which results when locking occurs can lead to vibration and unacceptable noise. The addition of properly-positioned bumpers is effective in suppressing such noise and in modifying its frequency to render a more customer-pleasing tone. However if the bumpers are set too ‘high’, that is they would enforce a greater than desired closure panel and body separation, the closure closing effort will be increased. Alternatively, if the bumpers are set too low they will not contact and support the closure panel and will be ineffective. Thus accurate setting of the bumper height is required for their proper functioning.
However, because every vehicle is built to tolerances, vehicle-to-vehicle variations in the fit of body panels will occur during vehicle assembly in a manufacturing plant. Thus the bumpers must be adjustable and incorporate at least the capability of compensating for, and accommodating, the expected vehicle build variation to assure the appropriate placement of the closure panel to achieve smooth vehicle lines and customer-pleasing closing tones in the assembled vehicle. Adjustment of such bumpers is often accomplished using trial and error and may require appreciable time and effort to achieve a desired build quality.
Once the bumpers are adjusted at the manufacturing plant to achieve proper placement, the need for further adjustment is minimal, but in-service adjustment may be required if either the body or the closure panel is repaired or replaced.
There is thus a need for an adjustable bumper which may be more quickly and easily adjusted, especially during vehicle assembly.
As shown in the simplified partial view of a front portion of an automobile 100 at
While bumpers are almost always found in the locations shown, there has been an increasing trend to provide additional bumpers, both to further support the latch-mounted edge of the hood, and also to better support opposed edges 114, 116. Thus, a plurality of supplementary bumpers may be attached to body portion 117 or its continuation 117′. During vehicle assembly, bumpers 113 are adjusted to appropriately locate the hood 110 in the body opening. Further adjustment in the course of normal vehicle service is usually unnecessary but may be required if, during service, the hood or its surrounding body portion is repaired or replaced. Such adjustment may require extensive trial and error to suitably position all the bumpers and the task will become increasingly burdensome as greater numbers of bumpers are used.
This disclosure pertains to adjustable bumpers for supporting and positioning closure panels on vehicles. The adjustable bumpers include a mounting portion comprising a mounting member or a mounting structure for attachment of the bumper to the vehicle body or to the closure panel. The mounting portion is attached to a mutually-centered material stack comprising at least a somewhat compliant, resilient body, often an elastomer, and a suitably shaped shape memory polymer (SMP) portion. The stack has a central longitudinal axis for receiving a load. Without limitation to their shape and design, and by way of illustration only, such bumpers may, in one embodiment be generally round or rectangular in cross-section with a diameter or side dimension of about 20 millimeters or so and extend outwardly from the body or closure by about 15 to 25 millimeters. The bumpers are mounted with their load-receiving central longitudinal axis generally perpendicular to the closing direction of the closure so that, when closed, the closure exerts a modest compressive force to the stack along the longitudinal axis of the stack.
SMPs are one of a group of “smart” materials, that is, designed materials with properties which may be controllably modified when exposed to an external stimulus. The property change may be abrupt and repeatable and such materials are increasingly being considered for automotive applications. Generally, SMPs may be phase segregated co-polymers comprising at least two different molecular segments within the SMP. The behaviors of each segment may be modified, commonly but not exclusively, by change of temperature, so that an SMP will exhibit a transition temperature demarking the influences of its various constituent segments. One segment is commonly considered to be a ‘hard’ segment and the other the ‘soft’ segment, with each segment contributing differently to the overall properties of the SMP in different temperature regimes.
When the SMP is heated above the transition temperature, the SMP will become appreciably more compliant, by up to a factor of 200 or so, and may be readily shaped into a desired configuration. The shape change may be made permanent by subsequently cooling the SMP below the transition temperature.
In an embodiment, a self-adjusting bumper comprises a relatively stiff elastomeric, closure-contacting portion, supported, in stacked configuration, on a quantity of SMP of suitable shape and configuration to form a short pillar or post and further comprising a body-engaging mount to secure the bumper to the vehicle body. In a second embodiment a relatively stiff elastomeric portion may support a stacked SMP portion, again in a pillar-like or post-like configuration. In this embodiment, because of the limited shock resistance of the SMP portion at in-service or ambient temperature, or about 25° C., the SMC portion may be ‘capped’ by a thin sheet of a compliant elastomer to diminish the shock of initial contact with the closure panel during closing. An exemplary SMP portion may be an unfilled, pore-free block, but bumpers may also accommodate SMP in other geometric shapes as well as be adapted to use filled and porous SMP formulations.
During installation and adjustment of the bumper, for example during vehicle assembly, at least the SMP portion of the bumper is heated to a temperature greater than its transition temperature and sufficient to render the SMP readily deformable. The bumper is affixed and secured to the vehicle body with the closure, for example the hood of
Under the most extreme conditions, vehicle components are expected to range in temperature from about 70° C. to 95° C., depending on their location on the vehicle. The transition temperature of the SMP portion should be chosen to be greater than the maximum expected in-service temperature to ensure that it remains in its low-compliance state during service and so undergoes no unintentional reshaping. Thus, the SMP portion may be formed of any suitable composition with a transition temperature of greater than about 70° C.-95° C., depending on location, to ensure that even on the hottest day, the SMP will not be exposed to temperatures greater than its transition temperature. Suitable compositions, among others, may include polymer components such as, polyphosphazenes, poly(vinyl alcohols), polyamides, polyimides, polyester amides, poly(amino acid)s, polyanhydrides, polycarbonates, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyortho esters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers, polyether amides, polyether esters, and copolymers thereof.
The SMP portion may be homogeneous, porous, with open or closed pores, filled with powder or fibrous fillers, or any combination of these. Any fillers may be thermally and/or electrically conductive. The SMP portion may incorporate channels or passages for passage or temporary storage of heated air or fluids to facilitate heating to above its transition temperature
The SMP portion may be in the form of a block, optionally partially laterally restrained within a polymeric or metallic sheath, and may be parallel-sided or tapered. Such a tapered configuration may be effective in the first embodiment of the device, enabling a wider body-mountable SMP base tapering to a reduced section to support the elastomeric portion. The SMP portion may also be shaped into various geometric forms with inherent geometrical compliances such as a helix or a bent beam.
The elastomeric portion may be a polyurethane elastomer or EPDM rubber (ethylene propylene diene monomer (M-class) rubber), a synthetic rubber and elastomer, suitably with a durometer of between 50 and 100, more preferably between 60 and 80. The contacting surface of the bumper may be smooth or have a texture such as, without limitation, bumps, ridges, or fingers to improve contact with the mating surface. The elastomeric portion should forcibly engage the mating surface to eliminate any momentary separation of the mating surface and the bumper under modest vibratory loading. Any such separation will produce noise due to the repeated separation and re-engagement of the bumper and mating surface. The polymeric portion composition is selected to avoid marring of the mating surface during contact and, further, to have a sufficient mechanical integrity so that polymer particles are not deposited on the mating surface when the closure is opened.
The body-engaging feature may include: a screw, for engagement with a body-mounted bolt; a bolt, for engagement with a body-mounted screw; a tabbed plate incorporating a plurality of tabs for tabular engagement with a like plurality of openings in a body member; any of a number of polymer-based push-in attachments such as Christmas Tree Clips, Stalok™ Fasteners (produced by ITW Fastex) and similar designs well known to those of skill in the art for engagement with suitable body openings; and a sheet metal support adapted for attachment to the body by welding or through the use of mechanical fasteners. The bumper may also be attached to the body with adhesive, for example, by the use of a double-sided adhesive tape.
Although it is feasible to adjust the bumpers after a vehicle is placed in service, it is anticipated that bumper adjustment will predominantly take place during vehicle assembly and build a manufacturing plant. During vehicle assembly it is anticipated that heating of the SMP would most commonly be conducted off-line, for example by heating under one or more infra-red (IR) lamps, or by placement in an oven or a heated fluid bath. However, heating in situ or after mounting of the bumper to the vehicle body using, for example, heat guns, or heaters with cavities, sized and adapted to accommodate the bumper, is also contemplated. If the SMP portions incorporate electrically-conductive fillers, the bumpers might be heated in situ by passage of electric current through the filler material. Of course, such in situ approaches may readily be adapted to in service adjustment of the bumpers if required.
In all descriptions so far, the bumper has been located on the body and the elastomeric portion has been in contact with the inner panel of the closure. It will be appreciated that the configuration may be reversed, that is, the bumper may be mounted on the closure and an elastomeric portion may contact the body provided only that such mounting does not mar the appearance of the outer panel of the closure or interfere with any included mechanisms.
A first embodiment of a self-adjusting panel closure bumper, or simply, bumper, 10 is shown at
Attachment feature 16, SMP portion 14 and resilient polymeric portion 12 are permanently connected to form a single assembly. In operation, the bumper 10 is subject to compressive loads generally directed along central, longitudinal axis 11. Thus there is no need to secure the portions against tensile loads which might tend to separate the portions, and bending and shear loads are expected to be low, so that a variety of attachment methods may be used, even those which are weak in tension. These attachment methods may include adhesives, mating, mechanically-engaging features, such as dovetails, and even frictional engagement between complementary features such as a shaped post and a close fitting complementarily-shaped opening.
Due to part and build variation the separation or spacing between vehicle bodies and closure panels exhibits a range of dimensions within an allowable tolerance range. A representative tolerance range is plus/minus 3 millimeters with respect to a nominal spacing. This variation in separation or spacing should be accommodated with a single bumper style, at least for a particular closure panel. Thus, the overall bumper length should be capable of spanning the largest gap between the body and closed closure panel which falls within this allowable tolerance range while maintaining forcible contact between the closure panel and the bumper. Also, the bumper must accommodate the large reduction in length or height, and associated compressive strain, resulting when a bumper, sized overall to span the largest gap within tolerance, must be compressed to a length suitable for the smallest gap within the allowable tolerance range. This places limits on the dimensions of the SMP portion since compression occurs at a temperature greater than the SMP transition temperature and so is sustained almost entirely by the SMP portion. Thus, for the representative tolerance range of plus/minus 3 millimeters cited above, the SMP portion should sized to be capable of accommodating up to 6 millimeters of reduction in height and sustaining the resulting strain, without detriment to its in-service performance. A number of SMP compositions are capable of compression to a true strain of greater than −1, or about a 63% reduction in length or height. Accordingly a preferred bumper may be between 20 and 30 millimeters long, with a cross-sectional area of between about 150 to 750 square millimeters. The lengths of the SMP and polymer portions may, but need not necessarily be, generally equal. A ratio of SMP length to polymer length ranging between about 80:20 to 30:70 is suitable. The square cross-section shown is exemplary only and not limiting.
Attachment feature 16 may be any suitable feature adapted to engage with either of a vehicle body or a closure panel and retain the attachment feature in a fixed location on the body or closure panel subject within the accepted tolerances of the specific attachment feature. Some exemplary attachment features, a portion of which are depicted in the alternative embodiments shown in
Polymeric portion 12 may be an elastomer, for example one engineered from the polyurethane family with a durometer hardness of between 50 and 100 at ambient temperature, and, more preferably between 60 and 80. Additionally, SMP portion 14 should be formulated to resist in-service aging which might lead to embrittlement which would be problematic under the dynamic loading experienced by the bumper in service.
SMP portion 14 may exhibit a wide range of compositions, but preferably the chosen composition will be harder than polymeric portion 12 at ambient temperature and appreciably softer than the polymeric portion 12 at an elevated temperature, designated the transition temperature, as described further below.
SMPs are co-polymers which may exhibit different properties in response to some external stimulus. In most cases the temperature of the SMP is the stimulus of choice, but electromagnetic radiation-responsive and moisture-responsive SMPs are available
Generally, SMPs may be phase segregated co-polymers comprising at least two different units, which may be described as defining different segments within the SMP, each segment contributing differently to the overall properties of the SMP.
The term “segment” may refer to a block, graft, or sequence of the same or similar monomer or oligomer units, which are copolymerized to form the SMP. Segments may be characterized as ‘hard’ or ‘soft’ and be crystalline or amorphous with corresponding melting points or glass transition temperatures (Tg), respectively. These segment characteristics result in a material which exhibits dramatic changes in properties under stimulus, notably changes in mechanical properties with temperature. Such materials exhibit a ‘transition temperature’ at which such property changes become manifest. SMPs may incorporate segments of multiple compositions and display multiple transition temperatures but, for the bumper application under consideration, two-segment SMPs with only a single hard and a single soft segment, and a single associated transition temperature, are suitable.
When the SMP is heated above its transition temperature, the SMP material can be more readily deformed than at a lower temperature and, and under application of a deformation-inducing load may readily assume a modified shape. Release of the deformation-inducing load when the SMP is above its transition temperature, will enable the SMP to revert to its undeformed shape. However, the modified shape may be retained by cooling the SMP below its transition temperature while the deformation-inducing load is applied.
The undeformed shape may be recovered by removing the deformation-inducing load and again heating the material above the transition temperature of the SMP. Thus repeating the heating, shaping, and cooling steps can repeatedly reset the deformed shape.
The transition temperature may be engineered by the choice of polymer constituents in the SMP and their proportions. Generally a range of transition temperatures of from between about 0° C. to about 300° C. are readily attainable. For the bumper application described further below, it is intended that the deformed shape of the SMP be maintained during normal vehicle service so that the SMP should be engineered to have a transition temperature greater than about 70° C. or so, and preferably greater than about 95° C. or so, since 70° C. to 95° C. is the highest temperature range normally attained by vehicle components even under extreme conditions. For ease of processing and handling of the bumper it is desirable to select an SMP composition with a transition temperature as close to the preferred range as possible. Making allowance for heat losses during processing, variability in batch to batch compositional variations, and day to day processing inconsistencies, suitable SMP compositions are preferably those with a transition temperature in the range of 70° C.-125° C. and more preferably those with a transition temperature in the range of about 95° C.-105° C.
Suitable shape memory polymers, regardless of the particular type of SMP, can be thermoplastics, thermosets-thermoplastic copolymers, interpenetrating networks, semi-interpenetrating networks, or mixed networks.
The SMP “units” or “segments” can be a single polymer or a blend of polymers. The polymers can be linear or branched elastomers with side chains or dendritic structural elements. Suitable polymer components to form a shape memory polymer include, but are not limited to, polyphosphazenes, poly(vinyl alcohols), polyamides, polyimides, polyester amides, poly(amino acid)s, polyanhydrides, polycarbonates, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyortho esters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers, polyether amides, polyether esters, and copolymers thereof
Examples of suitable polyacrylates include poly(methyl methacrylate), poly(ethyl methacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate), poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(lauryl methacrylate), poly(phenyl methacrylate), poly(methyl acrylate), poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecylacrylate). Examples of other suitable polymers include polystyrene, polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinated polybutylene, poly(octadecyl vinyl ether), poly (ethylene vinyl acetate), polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate), polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (block copolymer), poly(caprolactone) diniethacrylate-n-butyl acrylate, poly(norbornyl-polyhedral oligomeric silsequioxane), polyvinylchloride, urethane/butadiene copolymers, polyurethane-containing block copolymers, styrene-butadiene block copolymers, and the like. The polymer(s) used to form the various segments in the SMPs described above are either commercially available or can be synthesized using routine chemistry.
Particular SMP composition families (with transition temperatures in parentheses) which meet the desired range of transition temperatures include epoxies (90° C.-110° C.) and polyurethanes (95° C.-105° C.). A suitable specific formulation is a stoichiometric mixture of diglycidyl ether of bisphenol A epoxy monomer (Hexion EPON 826) and curing agent poly(propylene glycol)bis(2-aminopropyl) ether (Huntsman Jeffamine D230).
a)-(e) illustrate the process of setting or adjusting the bumper and its mode of use after setting.
At
The bumper, during processing, and after achieving its intended shape will apply a reaction load to the closure due to the elasticity of both the SMP and the polymer. The reaction load due to the SMP is maintained on ‘freezing in’ this shape as 14″ while the reaction load from the polymer will increase slightly due to the increased stiffness of the polymer at the lower operating temperature of the bumper. Such reaction load is desirable since it positively locates the closure panel and minimizes panel vibration and noise under vibratory loads.
It will be appreciates that the relative hardnesses, or compliances, of the polymeric portion 12 and SMP portion 14, at both ambient temperature and the processing temperature, will contribute significantly to the successful installation and application of the bumper. At ambient temperature, the compliance of the SMP should be less than that of the polymer, preferably by about a factor of 2 to 5 or so, to ensure that, during closure, the closure force primarily results in deflection of the polymer. Or, stated alternately, the stiffness of the SMP should be greater than that of the polymer by these factors. During installation and setting of the bumper it is intended that the deflection induced by the closure force is primarily accommodated by the SMP and the compliance of the SMP should be much greater than the compliance of the polymer, preferably by at least a factor of 5, more preferably by a factor or 10 and most preferably by a factor of 20. Expressed in terms of relative stiffnesses, the stiffness of the SMP should be less than that of the polymer by these factors.
By way of example only, consider a bumper of the embodiment of
The shape-modified bumper 10′ will retain its shape near indefinitely provided it never experiences temperatures at or above its transition temperature, so that, under normal usage, no further adjustment is required. However, if due to wear at the hinges, for example, or minor accident, or any other misadventure, the bumper no longer maintains the closure panel in its intended location, the process cycle shown at
As depicted at
Where in situ heating is required, any convenient heating method such as a hot air gun may be employed. Alternatively a hollow heater, optionally split longitudinally, and suitably customized and sized to just encompass the SMP portion could be used. If the SMP is filled with a portion of electrically-conductive powders or fibers in suitable concentration to form a continuous electrically-conductive path through the SMP, then resistance heating, effected by passage of an electrical current through the filled SMP may also be used.
A second bumper embodiment 20 is shown in
It may be noted that an alternative approach to geometrically-increasing the SMP compliance would be to incorporate a blowing agent into the SMP to render a porous SMP body with either open or closed pores. Where decreased compliance is desired, fillers, may be incorporated into the SMP. These may be fibers or powders and comprise electrically-conducting and thermally-conducting compositions such as metals or graphite, or electrically-insulating compositions such as ceramics or polymers or mixtures of both.
Another embodiment of a bumper is shown at
Practices of the invention have been described using illustrative examples which are not intended to limit the scope of the claimed invention.
