NO123313B - - Google Patents

Description

Laminated safety glass for vehicles,

which route is weaker near the input voltage

advised than in the middle surface.

The invention relates to windshields for vehicles.

Two different types are currently used for vehicle windscreens

glass and secondly multilayer glass or laminated glass. Single-

Laminated glass is glass that is in a state of tension, i.e. that the surface layer has a compressive prestress that is kept in equilibrium by a tensile prestress in the core of the front glass. The-ordinary laminate-

glass consists of two non-prestressed single front glasses that are connected to each other by means of a thermoplastic intermediate layer of polyvinyl butyral.

Single-layer safety glass remains in the event of breakage and shattering

in its entirety splintered in. small fragments. If a passenger is thrown against a windscreen of the type when the vessel suddenly brakes

single-layer safety glass, the front glass shatters if the passenger's head has a speed of 15 km/h and higher due to the local bending stress or bending pressure. The breaking process happens extremely quickly. Already after approx. 1 millisecond after the head comes in contact with the front glass, the glass is completely shattered and the passenger's head is free, so that there are no longer any braking forces on the head. Because of this extremely short operating time for the braking forces, only a very small part of the body's kinetic energy is absorbed by the front glass.

Also, the laminate safety front glass re-locks at certain impact speeds. When the polyvinyl butyral intermediate layer has a thickness of 0.38 mm, which has been common until now, you get - at an ambient temperature of approx. 20°C impact of the passenger's head at an impact speed of from approx. 25 to 30 .km/hour. In this case, however, the penetration of the passenger's head through the laminate safety disc has given rise to a very dangerous "necklace", i.e. a collar of sharp glass splinters along the edge of the fracture site, held firmly in the butyral foil, and this easily leads to life-threatening cuts.

To reduce the risk of penetration, the thickness of the butyral layer has been doubled. Such butyral interlayers are marketed e.g. under the trade names "High-Impact-Folien" or "Hig Penetration .Resistance-Folien". Such windscreens are smashed through by the passenger's head at approximately twice the impact speed, namely from approx. 45 km/h and above. When the front glass is not broken through, many times as much kinetic body energy is absorbed by this type of front glass than by a front glass with a butyral layer of 0.38 mm thickness, and this in the form of deformation work in the plastic intermediate layer and in the human organism.

In contrast to the single-layer safety front glasses, where the effect time of the impact forces is on the order of 1 millisecond, the effect time of the impact forces with the laminate front glasses,

due to the plastic deformation of the butyral interlayer, of a completely different order of magnitude. The duration of action in the case of impact from a human body is around 160 milliseconds.

When it comes to the passenger's collision with the windscreen and the resulting internal damage, however, it is now known that alongside the strength of the braking forces, the duration of action of these forces also plays a major role. The longer these forces are active, the less braking forces you can tolerate. The different human organs have a different resistance (tolerance limit) to deforming forces and their duration of action. They work like on

this subject area is best known, regarding loads and injuries in the human body when the forehead hits hard plates, originates from L.M. Patrick, Department of Engineering Mechanics, Wayne State University. These works are among other things published in the article "Human Tolerance to Impact - Basis for Safety Design". In this publication, L.M. Patrick, due to his experimental results for medium-sized concussions, drew up a tolerance curve for the permissible, effective braking effects (retardations) in dependence on the operating time. This curve already clearly shows how important the braking force's working time is for concussions.

It is also known that, in car accidents, you often see life-threatening cervical vertebra injuries stemming from the collision of the head with the windscreen. Statistics from road accidents that have been made public show that cervical spine injuries are significantly more dangerous than head injuries in terms of fatal outcome.

As a result of in-depth investigations, it has been found that safety windscreens with long impact times, especially the known laminate windscreens, under certain conditions that cannot be ruled out in practice, even at relatively low impact velocities can lead to low-risk damage to the cervical spine. Furthermore, it could be established that the possible tolerance limit for macroscopic cervical vertebra injuries is significantly lower than the mentioned tolerance limit for concussions (D. Ziffer, F. Briickner and R. Henn: "Das Verhalten der Halswirbelsåule in Verbindung mit der Schådelbasis und der oberen Brustwirbelsåule bei Stiirzen auf Sicherheitsglas flir Automobilfront-scheiben (Einscheibensicherheitsglas - Verbundsicherheitsglas)"

(Behavior of the Cervical Column in Connection with the Skull Base and Upper Thoracic Column in Impacts with Vehicle Frontal Safety Glass, (Single Layer Safety Glass - Laminate Safety Glass)), Zentralblatt fur Verkehrsmedizin, Verkehrspsychologie und an-grenzende Gebiete, December I967.)

Ijjffl_ge these investigations, damage to the cervical vertebral column can occur when the cervical vertebral column when a part of the body weight of around 15 kg presses upwards after the cervical vertebral column is dangerously exposed to bending or buckling stresses, and already at relatively low impact velocities. When the head hits a front glass made of laminated glass, this bulges out after the glass breaks during deformation of the butyral intermediate layer, in the impact area. In this way, the head is held firmly in a certain position and cannot slide or shift when the body mass presses on, so that during the period of action from the pushing body mass, apart from the dangerous sprains in the cervical region, one must expect a considerable bending load on the cervical vertebral column, which leads to said serious injuries.

The degree to which the cervical spine's resistance under these conditions is less than the brain mass's resistance - against concussions, can be seen from the following figures, which were measured in experiments with a 14 kg pushing mass in the direction of the cervical spine. While one knows a working time of. 50 milliseconds. calculated a tolerance limit for concussions according to L.M. Patrick at approx. 220 ^- Peffe^- iv> (the acceleration values indicated by L.M. Patrick were converted by multiplication with the average head weight of 4.5 kg,, to kp), according to experiments by.D. Digit with an equally long impact time against the front glass, serious damage to the cervical spine already at approx. 50 k<P>fficient.

These values apply to macroscopic damage to the cervical spine, such as e.g. ruptured intervertebral discs. If you also take into account microscopic damage, which can also be life-threatening, the values are even lower. An assessment of the experiments leads to the conclusion that, in principle, serious damage must be expected from bending and breaking of the cervical vertebral column when the impact process lasts longer than 30 milliseconds.

According to the invention, these new discoveries are taken into account, and a front glass type with improved properties is presented which, in the event of an impact from a human head, offers increased safety against internal damage by shortening the impact time.

A laminated safety glass pane according to the invention thus consists of two single sheets and a plastic intermediate layer, whereby the pane is weakened at the edge, so that in the event of an impact the central field breaks out while the edge zones remain in the frame and in which at least the outer single sheet consists of silica glass, and the safety glass pane is characterized by the fact that ..the plastic intermediate layer and the inner plate have a smaller area than the outer glass plate attached to the body's frame and at least over the largest part of its circumference is not attached to the frame, and that the plastic intermediate layer and/or the inner plate has such firmness that it does not break into pieces when hit by a spherical, rigid body with a weight of 20 kg and an impact speed of 50 km/h.

The effect of impact from the head against a windscreen of this type is as follows: A deformation wave emanates from the point of impact of the head, which deformation wave essentially propagates undisturbed within the central part of the windscreen and within 30 milliseconds. reaches the edge of the front glass. If now the middle part of the front glass has already been broken through or if the front glass has not yet been broken through with higher rigidity, the following conditions will exist: I

the moment the ion wave "deforms" when the edge of the front glass, the middle part of the front glass is cut off or separated from the edge area of the front glass which encloses the middle part, due to the energy of the deformation wave. The middle part is not punched through or broken through due to the required minimum strength, but dissolves after separation -sen from the clamping edge part completely or partially from the frame without dangerous braking forces acting on the head from the moment this release takes place. The release from the frame will in the following be called "release".....

In order for the front glass to be triggered, it is of course

a prerequisite that the impact energy has a certain minimum value. Furthermore, this depends on the thickness and strength properties of the clamped silicate glass plate at the edge areas. In further design of the invention, this can be achieved in principle by means of the dimensioning of the silicate glass sheet in this edge area or by influencing the firmness of other ways, which will be described later, set the threshold shock energy above which release will occur. Naturally, you do not want to set this release value too low, but on the other hand it is appropriate to set it to such a value that the front glass is only released at such high energies that serious damage is expected.

A first group of such designs is distinguished by

that it consists of a silicate glass plate and a connected plastic plate placed on the impact side, whereby the plastic plate is so

much smaller than the silicate glass plate, that it is not clamped in the frame, at least along the largest part of the circumference, and so that the front glass is secured by means of the outwardly projecting edge of the silicate glass plate, and that the plastic plate that covers the center field of the front glass consists of a non- brittle, preferably thermoplastic material, as within the temperature range -20 to +40°C

has a shear strength of at least 5 kp. cm/cm<2> according to DIN 53-453 and a tensile strength according to DIN 53*455 (0.1$ strain limit) of over 200 kp/cm<2>.

The thickness of the plastic sheet essentially depends on the material's tensile strength and elongation and should not exceed 3 mm because the impact forces then rise to unfavorable values.

According to a first exemplary embodiment, a silicate glass plate in the form of a windscreen according to this system consists of cooled, i.e. essentially stress-free, silicate glass with a thickness of 2 - 8 mm, preferably 2.5 to 6 mm. In this embodiment, release occurs when the silicate glass pane is cut off or cut off in the frame due to the deformation wave in the plastic plate.

According to another embodiment, the silicate glass plate consists of prestressed glass with a thickness of 2.5 to 6 mm. This design favors - release of the silicate glass sheet along the edge upon breakage of the prestressed sheet, namely by the inherent energy contained in the sheet due to the prestress, which energy is released upon breakage, so that the glass sheet shatters into small pieces right up to the edge section, whereby the fracture propagation speed is 1500 m/sec. In this case too, the propagation speed of the deformation wave is responsible for the complete detachment of the glass sheet and the braking against the head's own speed, and is therefore of decisive importance.

The stated minimum values for the shear strength and the tensile strength for. the plastic is necessary according to the invention so that the high deformation rates and tensile loads that occur upon impact can be tolerated by the plastic sheet without it breaking or plastically deforming to an undesirable degree. If the aforementioned limits are kept, even at the highest impact velocities that occur, practically no penetration occurs through the route. In addition to the solution, it is thereby also achieved that any direct contact between the human body and the glass edges is avoided.

Furthermore, a front glass composed of a glass sheet of non-prestressed glass can be provided with a weakening line along the plastic sheet's circumference, e.g. in the form of a crack in the glass surface, so that the solution or cut-off along this area is facilitated.

Another group of windshield types with the main features of the invention is characterized by the fact that the windshield consists of two single panes of silicate glass connected to each other over a plastic intermediate layer, where one pane of silicate glass is attached to the bodywork along the entire circumference and that the other single pane of glass covers the center field of the windshield, as well as the plastic intermediate layer has smaller dimensions than the glass plate that is attached to the frame, and is therefore not clamped in the frame, but instead ends before the frame edge, preferably along the entire circumference.

It has been shown that the movement speed of the deformation wave in a glass-butyral-glass composite plate meets the aforementioned requirements if the clamped glass plate has a thickness between 2 and 8 mm, and the non-clamped glass plate a thickness of between 0.1 and 3 mm . This also applies when the butyral layer has a thickness of 0.7 mm and higher.

The required shock-resistance force and the speed of the deformation wave can be achieved by choosing the intermediate layer material and/or its dimensioning. Will e.g. the inner smaller glass plate, made from silicate glass with normal strength, essentially becomes the intermediate layer responsible for the breakthrough strength. If one chooses polyvinyl butyral as an intermediate layer in such a design, this must have a thickness of at least 0.7 mm.

According to another embodiment, the outer glass sheet that is clamped in the frame can consist of chilled, i.e. not pre-stressed glass, and the other glass sheet that faces the passenger and is not clamped in the body frame, consist of glass that is thermal or chain- misc is prestressed and has high bending strength.

With this design, the necessary function is taken over, to give the front glass sufficient impact resistance for a large part of the prestressed glass plate with high bending strength. The bending strength of this glass sheet. should be so large that, at a not too high impact speed from the passenger's head, it can withstand the induced local deformation without breaking. In this case, the risk of cuts is practically eliminated.

In this embodiment, the adhesive layer does not need to have a high impact resistance as in the first-mentioned case. Depending on the bending strength of the inner glass plate, it may even be necessary to use particularly hard and brittle adhesives as an intermediate layer in order to thereby increase the propagation speed of the deformation wave, and thus achieve that the inner glass plate does not break before the front glass is released. Depending on the mechanical properties of the adhesive layer, this can in some cases even be clamped into the frame. This is the case when the adhesive is practically not exposed to any plastic deformation which leads to an extended impact time, but when the intermediate layer is also cut along the frame without any noticeable additional load for the passenger's head from the inner glass plate.

The requirements according to the present invention are also met by a windscreen where the glass plate which is attached to the body consists of pre-tensioned glass.

There is a particular advantage to this second group of front glass types if the inner, smaller glass plate has a thickness of less than 1.5 mm. Under these conditions, the risk of - the plastic intermediate layer breaking the inner glass plate being damaged by the fracture edges is particularly low, because the very thin glass plate due to its high flexibility gives way at the fracture edges and thus strongly reduces it for the plastic intermediate layer dangerous cutting effect.

Finally, it should be mentioned that both single glass panels can consist of thin glass panels with high bending strength, provided that it is ensured that. clamped edge area has such a low bending strength that the front glass is released on impact.

In an advantageous further development of the invention, the frame which occupies the front glass, or the rubber socket which is placed on the inside of the front glass, can protrude further over the edge area which exhibits lower bending strength and right into the main field of the front glass. This achieves that the edge part of the windscreen is supported on the inside even after breakage, so that the windscreen is prevented from being thrown into the passenger compartment in the event of an impact from the outside. Naturally, with such a design, you must ensure that there are no holding forces or adhesive forces between this supporting body part or the rubber profile and the high-bending fixed part of the glass plate, so that in any case the main field of the front glass is easily secured in the event of an impact from the inside released from the frame in an outward direction.

In the following, different embodiments of front glass according to the invention will be described, as well as the operation of the new types of front glass, in connection with individual force-time diagrams. Reference is also made to the drawings where: fig. 1 shows the principle structure for a front glass designed as laminate glass, and with the characteristic features according to the invention,

fig. 2 shows an appropriate design of the frame by

application of rubber profile,

fig. 3 shows another possibility for designing the frame by attaching the front glass by direct gluing to the bodywork,

fig. 4 shows different force-time diagrams measured by impact tests against front glass.

As can be seen from fig. 1 constitutes the part of the front glass plate that faces out in relation to the impact point formed by the silicate glass plate 1, which is held along the circumference in the frame 2. On the plate side facing the impact side is a smaller glass plate 3- This plate ends, preferably along the entire circumference, u-immediately in front of the frame groove for the silicate glass plate 1,. so that the smaller plate is not clamped in contrast to the larger one.

According to the aforementioned first group of designs, this smaller plate 3 consists of plastic.

The silicate glass plate 1 is connected to the plastic plate 3 by means of a suitable adhesive layer 5- The adhesive layer is advantageously of such a nature that the substance within the relevant temperature range absorbs the mechanical stresses that arise from the different thermal expansion of glass and plastic.

On the basis of the minimum values necessary according to the invention for the mechanical properties in the materials for the plastic sheet 3>, these materials can be selected from among the known sheets of plastics. E.g. mentioned conditions are met by a 0.25 w™ thick foil of polyterephthalic acid ethylene glycol ester, a 1 mm thick foil of high molecular weight thermoplastic polycarbonate of aromatic dihydroxy compounds, in particular bisphenylolalkanes, a 0.25 ^ thick foil of amorphous polyamide from an aromatic bifunctional acid, especially terephthalic acid, and an aliphatic alkyl-substituted bifunctional amine, especially hexamethylenediamine, or a 0.5 mm thick foil of a plasticizer-free polyvinyl chloride.

The smaller plate 3 can, according to the aforementioned second group of front glass types, also consist of silicate glass when it is ensured that either the plastic intermediate layer 5 or the silicate glass plate 3 or the entire laminate plate consisting of the individual layers 1, 3 °S 5 has the necessary impact resistance in the middle field . The glass plate 1 has a thickness of 2 - 8 mm and the glass plate 3 has a thickness of 0.1 to 3 mm' The plastic intermediate layer 5 consists of polyvinyl butyral and has a thickness of at least 0.7 mm.

Fig. 2 indicates a further developed design for the frame, where the smaller plate 3 is firmly supported against the inner side to prevent the front glass, if the outer glass plate 1 is crushed, by external influence, being pressed into the vehicle. For this purpose, the body's frame for the front glass, 10, is extended so much that the frame's upper part 11 projects over the edge along the plate 3. The rubber profile 12 is made wider at this point with a lip 13 that abuts against the plate 3. so that there is no adhesive force between the disc's 3 edges. and the rubber profile's lip 13, so that the plate 3 is easily triggered in the outward direction from the rubber profile in the event of accidents.

If you do not use a rubber profile, you can design the body frame with advantage as indicated in fig. 3. The framework 20

is bent into two steps, so that both the outer glass plate 21 and the inner plate 23 are inserted in each step. The outer plate 21 is firmly connected along the circumference by means of a. suitable adhesive material 24 with the bodywork 20. The inner plate 23, on the other hand, must not have any connection with the bodywork 20. For this purpose, a release agent 26 can be placed between the disc edge 23 and the frame part 25.

In fig. 4, a number of force-time curves have been produced which show the considerable reduction of the impact times in the event of impact against the available new front glass types. A simulator body was used for the experiments. a total of 20 kg weight. This weight is composed of the actual shock body which consists of a wooden head with a diameter of 19 cm and a weight placed behind this of 14 kg. This 14 kg weight simulates the part of the body mass that participates in the impact and this

.weight was chosen because in extreme cases one must expect that approx.

20 - 25% of the body mass transfers its kinetic energy to the head via the cervical spine. Between the wooden head and said weight, i.e. at the place corresponding to the neck vertebra, a measuring cell is placed to measure the forces that occur. This measuring cell weighs 1 kg, so that the total weight of the impactor is 20 kg.

This simulator body is dropped from different heights corresponding to the desired impact velocities, against a test plate with dimensions 50 x 110 cm. The test plates are clamped along the edge in different ways, namely in one case by applying a 56 kg heavy frame which corresponds to a clamping force of 120 p/cm<2>, and in another case by screwing this frame in such a way that one obtains an absolutely firm clamping in the same way as when gluing windscreens into car bodies.

One finds for such a rigid impact body, under the assumption of the same impact speed and the same impact mass, that this impact body has a higher impact force and a shorter total impact time, i.e. the impact force's operating time, than with natural bodies used for medical investigations. This is because the impact mass behaves differently, as the rigid simulator body participates with the entire mass from the beginning of the impact, while the human body on impact, due to the deformability of the body, participates in the impact more or less consecutively.

Despite these differences in measurement results, the significant advantages of the available new front glass types are clearly evident from these simulator tests.

All experiments were carried out with an impact speed of 22.5 km/h with the exception of trial I, where the impact speed was 19.7 km/h. In this case, the speed had to be set so low because the glass plate was broken at a higher speed and thus could not be used for comparison. The clamping conditions were kept constant during all tests, and the clamping forces were 120 p/cm<2>.

The listed curves reproduce the impact conditions against the following types of front glass: Curve In a normal laminated glass sheet consisting of two single glass sheets each 3.1 mm thick and a 0.38 mm thick polyvinyl butyral intermediate layer,

Curve II a laminated glass sheet with a polyvinyl butyral interlayer of 0.76 mm thickness,

Curve III a plate constructed according to the invention with a 4.2 mm thick, ordinary cooled silicate glass plate and a

0.25 mm thick polyester foil,

Curve IV a plate likewise constructed in accordance with the invention with a 4.2 mm thick silicate glass plate applied to stresses

by heat treatment, as well as a 0.25 n™ thick polyester foil.

All the curves show in principle the same characteristic course, which is characterized by two shock phases, namely a high power peak at approx. 1 millisecond. after the start of the impact and a portion of the force which joins the former but which, in relation to the peak of the force, extends over a significantly longer period of time. For the first impact phase, where the maximum force occurs which is necessary for the silicate glass to break, the thickness of the front glass is of significant importance, apart from the bending strength. In order for this power peak or power maximum not to reach dangerous levels, the thickness of the individual layers should not exceed the specified maximum values.

To get a better overview, the course of the force peak is only drawn for curve I, and otherwise the maximum value of this force peak is only indicated by II' to IV. After the silicate glass is broken or broken through, the power drops very quickly. Although the first power spike is very high, it is harmless in terms of internal damage, because the duration is extremely short.

However, the second power period is dangerous, and the invention relates precisely to the reduction of this force period, i.e. the resulting shortening of the entire impact process. The further course of the force curve is now essentially determined by the materials used in the middle field of the glass plate, i.e. the plate's conditions regarding plasticity and the propagation speed of the deformation wave.

Curve I can be left out of consideration as a front glass with such a structure is already broken or broken through by the simulator. The body when this has a speed of approx. 20 to 25 km/h and leads to dangerous "necklaces". But even at these low speeds, the total impact time is 38 milliseconds. The time increases at curve II to 60 milliseconds, whereby the effective force, i.e. the average force that acts in the second force period, simultaneously rises to 120 - 190 kp.

Compared to curve II (ordinary laminate safety glass - with "High Impact" interlayer), curves III and IV (front glass according to the invention) show the extent to which the overall impact time is reduced, as the impact time in both cases only amounts to approx. l6 milliseconds. The maximum forces are not noticeably affected, but with the short impact times now achieved, macroscopic cervical vertebra injuries are ruled out.

Numerous impact tests with other described embodiments of new front glasses according to the invention led qualitatively to the same result, i.e. in all cases to a considerable reduction of the impact time in relation to the known laminate safety glasses, so that it seems unnecessary to state more measurement results.

Claims (7)

1. Laminated safety glass pane for vehicles consisting of two single panes and a plastic intermediate layer, which pane is weakened at the edge, so that in the event of an impact the central pane breaks out while the edge zones remain in the frame, and in which at least the outer single pane consists of silicate glass, characterized by the plastic intermediate layer (5) and the inner plate (3, 23) have a smaller area than the outer glass plate attached to the body frame (2, 12, 24) - "(1, 21) and at least over the largest part of its circumference is fixed in the frame, and that the plastic intermediate layer (5) and/or the inner plate (3, 23) has such strength that in the event of an impact from a spherical, rigid body with a weight of 20 kg and an impact speed of 50 km per hour not broken. 2. Tempered safety glass pane according to claim 1, characterized in that the inner plate (3 > 23) consists of a non-brittle, preferably thermoplastic plastic, as in the temperature range. between -20° and +4°°C has a chip impact strength according to DIN 53*453 Pa of at least 5 kp. cm/cm2 and a tensile strength according to DIN 43.455 (0.1$ elongation limit) of more than -200 kp/cm<2>. 3. Laminated safety glass pane. according to claim 1, characterized in that the inner plate (3, 23) is a silicate glass plate with a thickness of less than 3 mm and preferably less than 1 mm, and that the plastic intermediate layer is a layer of polyvinyl butyral with a thickness of at least 0 .7 mm. 4. - Laminated safety glass pane according to claim 3j characterized in that the inner glass plate (3, 23) consists of a glass with high bending strength, e.g. of a by means of ion exchange ■ling surface-treated glass. 5. Laminated safety glass pane according to one or more of claims 1-4, characterized in that the edge area of the outer clamped silicate glass plate (1, 21) has such strength that it breaks into pieces under a shock load corresponding to the impact of a 5 kg impact body with an impact speed of 30 km/h. 6. Laminated safety glass pane according to claim 5> characterized in that the outer, clamped silicate glass plate is thermally prestressed and in the edge area has a pressure prestress in the order of magnitude between 10 and 20 kg/mm<2>. 7..Laminated safety glass pane according to claim 5 or 6, characterized in that the outer, in the frame attached glass plate on its inside along the fastening in the frame is equipped with points of weakness or a line of weakness which favors breakage at this point.