Energy absorbing mounting systems for vehicle windows

Abstract: The invention describes plastic automobile windows 4 that are safe during side impact collisions, including a method for installing the windows into the motor vehicle. The mounting system and window material will contain an occupant in a vehicle at low to moderate head impact velocities. The occupant is not subjected to head injuries. The occupant is not subject to lacerations. The window design uses a high modulus transparent thermoplastic, having an abrasion resistant coating 10. The window is attached to the window opening in a motor vehicle by using one of several mounting techniques e.g. 16 as described herein. For fixed windows, the mounting systems will bond the window to the vehicle under normal operating conditions and provide a weather seal. For a movable window, the window frame will be equipped with a sliding track and provide a weather seal. A groove or notch 9 in the window material inward from the edge in combination with the mounting systems enhance a safe release of the plastic window. By choosing the thickness of the window and specific mounting technique, the plastic window can be made to be pushed out, so that the window remains intact and no injury is made to the impacting occupant's head. The mounting system is designed so that the window will be pushed out and be released from the vehicle in a safe manner. The breakaway zone 9 in the window will break along a notch cut or molded into the window. The window will break and any fragments will be safely released from the window frame by a notch breaking.

Description: The present invention relates to energy absorbing mounting systems for vehicle windows, particularly for automobiles, which are safe for impact collisions, and in particular vehicle impact collisions. Side and rear windows in motor vehicles are currently manufactured from float glass that has been tempered. Tempering of glass places the two outer surfaces of the glass into compression. Therefore when the glass is impacted it will shatter into very small pieces. Tempered glass has replaced annealed glass in window openings of motor vehicles. Annealed glass breaks into large dagger-like shards that can easily lacerate and seriously injure a vehicle occupant. While tempered glass has reduced lacerations, there remain several problems. Tempered glass can cause laceration of an occupant because the small fragments have very sharp edges; and if a tempered glass window breaks, pieces of glass remain embedded in the edge of the window. This may cause parts of a person's body to be raked along the edge of the window and result in serious lacerations. Since tempered glass will shatter, it does not offer the vehicle occupant any protection from being ejected from the passenger compartment. If the vehicle is impacted from the side, the passenger could be partly or wholly ejected out through the window opening. If the vehicle begins to tumble in a rollover then the occupant could be partially or fully ejected and could incur a serious or a fatal injury once parts of the body are outside the vehicle. Some work is known that attempts to improve the laceration and containment deficiency of tempered glass. Windshields, for example, are composed of two layers of glass separated with a thin layer of plastic. The inner layer, made of poly (vinyl butyral), holds the broken glass together upon vehicular impact. A further refinement is found in that a second plastic layer is applied to the inner surface of the window. A moveable window design with a combination of an inner plastic layer and an outer glass layer is known. This window is intended to contain the occupant within the vehicle during a side impact collision. This is accomplished by a multi-part structure composed of a plastic frame that moves up and down in a special track design. The plastic frame has an edge in the shape of a "T," and acts to sandwich together the outer glass layer and the inner plastic layer. The disadvantages are that the inner plastic layer is prone to scratching, reducing driver visibility, and the frame adds weight to the glazing structure. A few inventions have been described using thermoplastic window for motor vehicles. US-A-4,635,420 describes an acrylic window material that is ultrasonically welded to a plastic gasket. A safety feature is disclosed where grooves or notches are placed inward from the edge of the acrylic window to facilitate breakaway zones. Two disadvantages in this type of gasket installation are that it is not commonly used by original equipment manufacturers and is not economical to manufacture. Another patent describes a synthetic resin window for a vehicle that has a frame or gasket molded from the same synthetic resin material.' This window is lightweight yet does not incorporate any feature that makes it safe during a potential side impact collision. The invention for which protection is sought is defined in claims 1 to 9. It would be desirable to use a monolithic glazing structure composed of a thermoplastic resin with a window mounting system that can reduce lacerations, produce no head injuries and provide occupant containment. A further benefit may be from a reduction in weight of the window structure. The invention will now be described, by way of example, with reference to the following Figures in which: FIG. 1 is a perspective view of a side window module for an automotive vehicle according to one preferred embodiment of the invention; FIG. 2 is a fragmentary cross-sectional view of an embodiment of a sheet of thermoplastic glazing material; FIG. 3 is a schematic representation showing other variations in the embodiment of FIG. 2: Referring now to FIGS. 1, 2 and 3, there is shown a synthetic resin window according to one embodiment of the present invention, which may be used in an automotive vehicle. The window module is designated by reference numeral 1, and is made of an appropriate thermoplastic resin by means of an injection molding or thermoforming process, as will be described hereinafter, and secured to a relevant vehicle chassis panel 6 with a mounting system. The window module 1 includes a window body portion 4 in the form of a sheet of transparent or semi-transparent synthetic resin, such as polycarbonate resin, acrylic resin or polyglutarimide resin. The window module 1 further includes a frame portion 5 extending along the peripheral edge of the window body portion 4. An abrasion resistant coating 10 covers the surfaces of the window body portion 4. A pressure sensitive foam tape 16 can be used as hereinafter described. A notch or groove 9 cut or molded into the window body portion 4 will enhance the formation of a breakaway zone 14. In FIG. 2 and FIG. 3 embodiments, notches or other shaped grooves 9, are cut or molded into one or both sides of the synthetic resin glazing material. Some of the possible shapes shown in FIG. 3 can be cut or molded into the synthetic resin glazing materials as taught by US-A-4,635,420. A double sided adhesive foam strip 16 is adhered around the edge of the glazing material. The thermoplastic resin can be any high modulus transparent material, such as poly (methyl methacrylate) (PMMA), impact modified poly (methyl methacrylate), acrylic copolymers, poly (methyl methacrylate-co-alkyl acrylate) wherein the alkyl group contains 1 to 8 carbon atoms, acrylic blends, acrylic alloys, poly (vinyl chloride), poly (styrene-co-acrylonitrile) wherein the acrylonitrile polymer comprises up to 40% of the copolymer, polycarbonate, poly (ethylene terephthalate), polystyrene, poly (styrene-co-methyl methacrylate), poly ( alpha - methylstyrene-co-methyl methacrylate), poly ( alpha -methylstyrene-co-alkyl acrylate) wherein the alkyl group contains 1 to 8 carbon atoms, poly (vinyl acetate), poly (ester carbonate), polyarylate, poly (ether sulfone), or polyetherimide. One such acrylic copolymer could be a polyglutarimide and poly (methyl methacrylate) copolymer, also known as poly (methyl methacrylimide) (PMMI), i.e., US-A-4,246,374; 4,217,424; and 4,727,117 assigned to Rohm and Haas Co.; and others. The thermoplastic glazing material meets the following criteria: an elastic modulus in the range of 2.0 to 4.2 GPa, a coefficient of thermal expansion of 4 to 8 × 10 -5 cm/cm/° C at room temperature, and a continuous service temperature of at least 70° C or more for an acrylic thermoplastic. Ranges for other thermoplastic resins are above about 115° C for PMMI, and above about 110° C for polycarbonate. These conditions provide a window that will not flutter when driven at high vehicle velocities, does not greatly expand its dimensions with temperature and maintains its integrity at the high temperatures that vehicles can reach. It is possible that plastic fillers, impact modifiers, coefficient of thermal expansion modifiers, continuous service temperature modifiers, stiffness modifiers, such as glass fillers; other plastic additives, and stabilizers can be used to modify other thermoplastic materials to these performance criteria by any person knowledgeable in plastic compounding technology. These glazing materials may be colored or tinted, for example, to reduce solar transmission levels. Any of the above thermoplastics are usually formed into the shape and size of a window by using sheet or molding powder (pellets). The thermoplastic sheet can be from about 1.5 to 6 mm in thickness and drape-formed or thermoformed using an appropriate mold. The plastic sheet is heated to a temperature so that it softens and can easily take on the shape of a mold. Another technique to form the windows is to injection mold pellets of the thermoplastics in an injection molding machine that will fill a mold cavity with the molten plastic material. The specific molding conditions are highly dependent on the thermal and flow properties of the material. For an optical application, it is best to mold under conditions that provide for the least amount of residual stress in the molded part. The window thickness can be from between about 1.5 to 6 mm. The window 4 used in this invention has been treated on both sides with an abrasion resistant coating 10. This provides a hard surface that is not easily scratched. Coatings such as polysiloxanes, transparent thermosetting resins, UV-curable coatings, polyurethanes, or diamond-like abrasion resistant coatings may be practical for this use. Coatings may be applied by plasma deposition, ion implantation, ion-assisted coating, evaporation, sputter deposition, physical or chemical vapor deposition, thermal spraying, and plasma assisted depositions. Other abrasion resistant coatings are known in the art. Before the coating process begins, the thermoplastic part is annealed in an oven to remove any residual stress. The polysiloxane used in this invention is applied in conjunction with a primer and is typically coated by dipping the plastic glazing part into a liquid coating solution. However, flow, sprayable, curtain and other coating techniques may also be used. After each coating step the part is dried in an oven at elevated temperature. Any hard coating could be used, though it would have to be compatible with both the thermoplastic and the mounting system. One adhesive used in this invention is a foam tape, made from acrylic based materials, and has a pressure sensitive adhesive on both sides of the tape. Or the tape could have a hot melt adhesive. The tape is typically 5 mm to 26 mm wide and from 1 mm to 7 mm thick. The foam density should be about from 0.3 to 0.8 grams per cubic centimeter. Other kinds of tapes could be used for the attachment of the thermoplastic window, such as polyurethane, or neoprene or any other type of foam material that can be formed into a tape with two adhesive layers. The tape should preferably be water and weather resistant. Any of these materials could be enhanced so that they meet these criteria by adding additives, stabilizers, plasticisers and blowing agents known in the art. The foam density is of importance in the performance of this invention. For instance, it has been shown that a tape of density in the lower part of the range given will tear during an impact to the plastic window, but a foam in the higher part of the density range will not tear. If the window does break, the foam with the higher density will more likely hold broken pieces in the plane of the window and may cause lacerations. The pressure sensitive adhesive on the vehicle side of the tape should be formulated to adhere well to the paint systems used on motor vehicles. The adhesive strength between the tape and the plastic or paint surface should be higher than the cohesive strength of the tape. A cohesive failure of the tape can be predicted by its mechanical properties. An attachment system such as Velcro could be engineered to provide the energy absorbing design to hold the thermoplastic window at low to moderate head impact velocities. At high head impact velocities, the specially designed Velcro attachment system could then rip itself apart, safely releasing the window module. In combination with any of the above mentioned window mounting methods, a notch or groove 9 may be placed inward from the edge of the plastic window to provide a breakaway zone. Various types of notches are disclosed in U.S. Pat. No. 5,035,096. Any combination of notches could be used in conjunction with the window mounting techniques to define specific breakaway zones 14 in the plastic window. The notch depth is preferably between 10 and 80% of the thickness of the plastic window. In the breakaway zones the radius can be from about 5% of the part thickness to about 200% or more of the part thickness, and may be molded , cut, or machined into the thermoplastic glazing. The notch is designed in terms of radius, type of cross section, location along the perimeter (along any number or sections of the sides of the window), distance inward from the edge (1 to 100 mm, for example, so as to aesthetically pleasing) and depth, so that the section of the window inward of the notch or groove will break out along the notch at relatively high impact velocities, for example, above 32 kilometers per hour. At low to moderate head impact velocities, for example, 0 to 32 kilometers per hour, the notch should not break. This will provide for containment of the occupant under less severe impact conditions, greatly reducing the possibility of ejection of the occupant from the vehicle through the window opening. This invention is based on mechanical and physical properties of the plastic glazing material and the mounting system used to bond the plastic to the vehicle window opening. Tempered glass is a very high modulus, brittle material that is designed intentionally to break into small fragments upon impact. However, tempered glass breaks at an impact velocity that is relatively low compared to the typical crash velocities as specified in several government testing procedures (see 49CFR 571.214, below). The properties of the thermoplastic materials in the invention are such that the plastic window will not break at the head velocities where tempered glass shatters, for example below 23 kilometers per hour. If used in combination with the mounting systems mentioned above, the whole glazing structure will be stretched or deflected out from the vehicle structure. By judiciously choosing the thickness of the window and specific mounting system, the window module can be made to be pushed out so that the window remains intact and limits the likelihood of injury to the impacting occupant's head or body parts. At very high head impact velocities the mounting system can be designed so that the window will be released from the vehicle in a safe manner. Either the window will detach itself from the mounting system, break along the breakaway zone cut into the window, or the window will break and any fragments will be safely released from the window frame by a notch breaking or, in one case, by a foam tape ripping itself apart. This invention is used for mounting plastic windows into motor vehicles. The types of windows are: windshields, moveable windows as found on the side of motor vehicles, side windows that do not move, opera windows, flipper windows, or other types of venting windows, and back windows. Types of motor vehicles are passenger cars, light trucks, multi-purpose vehicles, off-road vehicles, heavy trucks,buses, recreational vehicles and motor homes. The invention will now be described by way of the following Examples. In the following Examples, Head Injury Criteria (HIC) is determined in accordance with the following formula from 49CFR 571.208: where a = the resultant head acceleration expressed as a multiple of g (the acceleration of gravity), where t 1 and t 2 are any two points in time during the impact which are separated by not more then a 36 millisecond time interval and where t 1 and t 2 are selected so as to maximize Eq. (1). If the HIC value is below 1000, then 49CFR 571.208 states that the potential for head injury is unlikely. If the HIC value is above 1000, then the potential for head injury is possible. The Chamois Laceration Scale is as follows: 0 Superficial Cuts Pass 1 Outer Layer Cuts Pass 2 Inner Layer Cuts Fail (Reference Society of Automotive Engineers Paper Number 860198 (1986).) EXAMPLES Example 1 Extruded sheet of PMMI, 5 mm thick, is thermoformed into the shape and size of an automobile side quarter window. The plastic window is coated with an abrasion resistant coating, i.e., a polysiloxane. The window is pre-treated with a liquid primer and cleaner. Two automotive foam tapes, with densities in the range of 0.5 to 0.65 and 0.6 to 0.75 grams per cubic centimeter, and 6.2 and 12.5 mm wide, are pressed onto the treated surface. The window and tape are then installed adhesively into a quarter window frame opening by revealing the second side of the foam tape. The window is tested by launching a human surrogate head (49 CFR572E defines head and geometry) at 26, 34 and 40 kilometers per hour towards the window. Data are collected regarding the head deceleration upon impact, the disposition of the window and any fragments, and the laceration is measured using a two-layer chamois skin placed over the head. The disposition, chamois laceration values, and HIC values of the window or its fragments are shown below. Head Velocity (km/hr) Tape Density (gm per cc) Tape width (mm) Window Disposition Chamois Laceration Scale Head Injury Criteria 26 0.5 to 0.65 12.5 no break 0 <1000 34 0.5 to 0.65 12.5 break 0 <1000 34 0.5 to 0.65 12.5 no break 0 <1000 40 0.5 to 0.65 12.5 no break 0 <1000 26 0.6 to 0.75 12.5 no break 0 <1000 34 0.6 to 0.75 12.5 break 0 <1000 40 0.6 to 0.75 12.5 break 0 <1000 30 0.5 to 0.65 6.2 no break 0 <1000 Example 2 Extruded sheet of PMMI, 5 mm thick, is thermoformed into the shape and size of an automobile side quarter window. The plastic window is dip coated with a polysiloxane abrasion resistant coating. A notch in the shape of a letter v, with a 60° angle, is cut 14mm inward from the outer edge of the window. The notch in several cases is from 2.5 to 3.0 mm deep. The window is pre-treated with a liquid primer and cleaner. Two automotive foam tapes, with densities in the range of 0.5 to 0.65 grams per cubic centimeter, and 12.5 mm wide, are pressed onto the treated surface. The window and tape are then installed adhesively into a quarter window frame opening by revealing the second side of the foam tape. The window is mounted to the window aperture in a portion of the vehicle chassis panel. The window module is then tested by launching towards the test fixture a human surrogate head (49 CFR572E defines head and geometry) at 26, 34 and 40 kilometers per hour. Data are collected regarding the head deceleration upon impact, the disposition of the window and any fragments, and the laceration is measured using 2 layers of chamois skin placed over the head. The disposition, chamois laceration values, and HIC values of the window or its fragments are shown below. Head Velocity (km/hr) Notch Depth (mm) Window Disposition Chamois Laceration Scale Head Injury Criteria 26 2.5 no break 0 <1000 34 2.5 break along notch 0 <1000 34 2.5 break along notch 0 <1000 40 2.5 break along notch 0 <1000 40 2.5 break along notch 0 <1000 24 3.0 no break 0 <1000 30 3.0 break along notch 0 <1000 33 3.0 break along notch 0 <1000 Example 3 Extruded sheet of PMMI, 5 mm thick, is thermoformed into the shape and size of an automobile side quarter window. The plastic window is dip coated with a polysiloxane abrasion resistant coating. A notch in the shape of a letter v, with a 60° angle, is cut 14mm inward from the outer edge of the several window. The notch is 3.0 mm deep. The window is pre-treated with a liquid primer and cleaner. An automotive foam tapes, with densities in the range of 0.5 to 0.65 grams per cubic centimeter, and 6.2 and 12.5 mm wide, are pressed onto the treated surface. The window and tape are then installed adhesively into a quarter window frame opening by revealing the second side of the foam tape. The window is mounted to the window aperture in a portion of the vehicle chassis panel . The vehicle chassis panel adjacent to a vehicle seat is firmly attached to a test structure. A 50 th percentile male anthropomorphic side impact dummy (SID) (49CFR572F) with a Hybrid III head (49 CFR572E). The window module is then tested by accelerating the whole test structure (dummy on bench adjacent to vehicle chassis panel) using a HYGE sled, where this acceleration results in head impact velocities of 36 to 37 kilometers per hour. Data are collected regarding the head deceleration upon impact, the disposition of the window and any fragments, and the laceration is measured using 2 layers of chamois skin placed over the head. The disposition, chamois laceration values, and HIC values of the window or its fragments are shown below. Head Velocity (km/hr) Tape Width (mm) Notch Depth (mm) Window Disposition Chamois Laceration Scale Head Injury Criteria 42 12.5 3.0 break along notch 0 <1000 38 12.5 3.0 break along notch 0 <1000 38 6.2 0 window pop-out 0 <1000

Claims: A vehicle window frame assembly comprising a vehicle window frame and a sheet of transparent thermoplastic polymer glazing positioned in the window frame and releasably attached thereto the assembly being characterised in that the thermoplastic polymer glazing has: 1)an elastic modulus of from 2.0 to 4.2 GPa, 2)a coefficient of thermal expansion of from 4 to 8x10 -5 cm/cm degrees C at room temperature, and 3)a continuous service temperature of at least 70 degrees C and in that the means for releasably attaching the thermoplastic polymer glazing to the window frame is an adhesive foam tape circumferentially positioned around the window frame whereby a)the glazing remains attached to the window frame at low to moderate head impact velocities against the glazing and b)the glazing becomes detached from the window frame at high head impact velocities against the glazing. A vehicle window frame assembly as claimed in claim 1 wherein the sheet of thermoplastic polymer glazing is a material selected from poly(methyl methacrylate) (PMMA), impact modified poly(methyl methacrylate), acrylic copolymers such as poly(methyl methacrylimide) (PMMI), poly(methyl methacrylate-co-alkyl acrylate) wherein the alkyl group contains 1 to 8 carbon atoms, acrylic blends, acrylic alloys, poly(vinyl chloride), poly (styrene-co-acrylonitrile) wherein the acrylonitrile polymer comprises up to 40% of the copolymer, polycarbonate, poly (ethylene terephthalate), polystyrene, poly (styrene-co-methyl methacrylate), poly ( alpha -methylstyrene-co-methyl methacrylate), poly ( alpha -methylstyrene-co-alkyl acrylate) wherein the alkyl group contains 1 to 8 carbon atoms, poly(vinyl acetete), poly (ester carbonate), polyarylate, poly(ether sulfone), or polyetherimide and mixtures thereof. A vehicle window frame assembly as claimed in claim 1 or claim 2 wherein the said sheet of thermoplastic polymer glazing comprises a notch or groove on the inside or outside of the sheet thereby providing a breakaway zone. A vehicle window frame assembly as claimed in any preceding claim wherein the sheet of thermoplastic polymer glazing is 1.5mm to 6mm in thickness. A vehicle window frame assembly as claimed in any preceding claim wherein the adhesive foam tape is a double-sided tape 5mm to 26mm wide, 1mm to 7mm thick and has a density of 0.3 to 0.8 grams per cubic centimeter. A vehicle window frame assembly as claimed in any preceding claim wherein the sheet of thermoplastic polymer glazing material is coloured, tinted or treated for solar control. A vehicle window frame assembly as claimed in any preceding claim wherein the sheet of thermoplastic polymer glazing material is coated with an abrasion resistant coating. A vehicle window frame assembly as claimed in any preceding claim wherein the adhesive foam tape means is selected from tapes made from acrylic, polyurethane or neoprene. A vehicle window frame assembly as claimed in claim 3 wherein the notch or groove is 10% to 20% of the thickness of the thermoplastic polymer glazing and wherein the notch or groove is 1mm to 100mm from the perimeter edge and wherein the notch or groove is on one or more sides of the window perimeter or parts thereof.

Inventors: JANS ROBERT WILLIAM, RAYMOND PAUL JOHNSTON, REILLY JOHN JOSEPH, JANS, ROBERT WILLIAM, RAYMOND, PAUL JOHNSTON, REILLY, JOHN JOSEPH
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 1993
Main classification: B60J10
IPC codes: B60J10, B29L31, B29D12, B60J1, B29C45, B29D99