JPS6157504B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to impact energy absorbing bumpers, particularly impact energy absorbing bumpers for vehicles. In recent years, the US Vehicle Safety Standards (MVSS=Motor Vehicle Safety Standards) have been adopted for automobile bumpers.
The need for impact energy-absorbing bumpers is increasing due to regulations such as Japan Standard) and increasing social needs for pedestrian protection. To date, various types of bumper systems have been devised and put into practical use as measures to meet this demand. For example, (1) A hydraulic shock absorber is attached to a highly rigid metal bumper beam, and the metal beam does not undergo permanent deformation due to impact.The impact force is transmitted to the hydraulic shock absorber, and the hydraulic shock absorber in the hydraulic piston is A type that absorbs impact energy using the viscous flow of oil. (2) It is made of synthetic resin or synthetic rubber, and has a number of rib structures on the back side of the skin as required, and in the event of an impact, the impact energy is absorbed by the buckling of the rib structures. type (generally
(3) An outer skin made of synthetic resin or synthetic rubber, and a thermoplastic resin, etc., placed inside the outer skin by injection molding. The bumper system consists of a honeycomb structure made of aluminum and a back-up beam located behind these to hold them.In the event of an impact, the bumper system absorbs the impact energy by buckling the honeycomb structure ( For example, see US Pat. No. 3,997,207) (4) An outer shell made of synthetic resin or synthetic rubber and a relatively low density (0.1 to 0.3 g/
A bumper system consisting of a semi-rigid impact energy-absorbing urethane foam (approximately cm ³ ) and a back-up beam located behind and holding them. A type that absorbs impact energy by compressing and deforming an energy-absorbing urethane foam (for example, U.S. Patent No. 3866963)
There are various types of impact energy absorbing bumper systems such as (see specification), each of which is effective to a certain extent, but each has its own merits and demerits, and there are still impact energy absorbing systems that exhibit satisfactory performance. Bumper systems have not yet been provided. In other words, in the hydraulic shock absorber type bumper (1), the stress applied to the bumper beam due to impact is absorbed by the bumper. permanent deformation of the beam,
In order to transmit the transmission to the shock absorber without causing damage, the bumper beam must be a rigid body with high strength, and therefore high-strength steel plates are used, which has the disadvantage of increasing the weight of the bumper. However, since the bumper beam is made of metal, it has the problem of rusting. Furthermore, due to its mechanism, such a hydraulic shock absorber can only effectively perform its function against stress components in the axial direction of the hydraulic piston.
Although it functions effectively against impact from the front of the bumper, it does not function effectively against impact from an oblique direction. (2) In the case of a high-flex type bumper that absorbs impact energy through buckling of the rib structure, it is difficult to predict the buckling behavior, so it is difficult to predict the buckling behavior, so the shape of the rib structure is effective in order to exhibit good performance as a bumper. , arrangement, number, etc. are difficult to design. Furthermore, since the bumper has a rib structure, it has a complicated shape with many unevenness, which results in poor moldability when manufacturing the bumper. Furthermore, from the decorative point of view of an automobile bumper, sink marks along the rib structure, called sink marks, occur on the bumper surface portion corresponding to the position of the rib structure, which is undesirable. In addition, the entire bumper is made of a highly rigid polymeric material, and the modulus of the material itself is temperature dependent, meaning that the modulus decreases at high temperatures and increases at low temperatures, so the temperature dependence of the modulus becomes large. In order to absorb a certain amount of impact energy, it is forced to undergo large deformations at high temperatures, resulting in a so-called bottoming out state and an increase in the generated load. Furthermore, at low temperatures, the modulus becomes high even with moderate deformation, so the generated load becomes large. and,
Since this large stress generated in the bumper is transmitted to the automobile body, a vehicle to which this type of bumper is installed has the disadvantage that it is necessary to design the body to have a large strength. In the type of bumper (3) that absorbs impact energy by buckling the honeycomb structure, upon impact, the buckling of the honeycomb structure causes permanent deformation, cracking, and destruction of the honeycomb structure, resulting in poor recovery. Also,
Honeycomb structures are usually molded from thermoplastic resin materials, but thermoplastic resins generally have a large modulus dependence on temperature, and even in honeycomb structures, there are differences between impact behavior at high temperatures and low temperature. This has the disadvantage that there is a large difference in behavior from impact. Furthermore, it is composed of (4) a synthetic resin or synthetic rubber outer shell, a semi-rigid impact energy absorbing urethane foam placed inside the outer shell, and a back-up beam, and when the urethane foam is compressively deformed, In impact energy absorbing types of bumpers, a semi-rigid impact energy absorbing urethane foam is placed inside the outer skin, so that the impact stress generated locally in the bumper during an impact is quickly distributed evenly over the entire foam. As a result, this distributed stress is transferred to the backup beam, reducing the required mechanical strength of the backup beam and reducing the weight of the backup beam. can do. The impact energy absorbing urethane foam is typically 0.1 to 0.3
Low densities in the range of g/cm ³ are often used, and their weight is also small, which, combined with the aforementioned back-up beam weight reduction, significantly reduces the overall weight of the bumper. However, the modulus of the impact energy absorbing urethane foam is temperature dependent, and the modulus decreases at high temperatures and increases at low temperatures, so it is difficult to absorb a certain amount of impact energy. , at high temperatures, it is forced to undergo large deformations, resulting in a so-called bottoming out state, and the generated load increases. Furthermore, at low temperatures, the modulus increases even with moderate deformation, so the disadvantage that the generated load increases cannot be avoided. Furthermore, the energy absorption efficiency of commonly used impact energy absorbing urethane foams is usually 50 to 70%, which is still not a fully satisfactory performance. As mentioned above, although the various impact energy absorbing bumpers that have been proposed to date are effective to a certain extent, they cannot be said to have sufficiently satisfactory performance, and the weight of the bumper,
It could not be said to be economical from a cost standpoint. The present invention has focused on the above-mentioned drawbacks and has been proposed to improve the problem, and includes a synthetic resin or synthetic rubber outer skin, an impact energy absorbing foam disposed inside the outer skin, and a shock energy absorbing foam located behind the outer skin. In the bumper system, which consists of a back-up beam that holds these, the impact energy absorbing foam is composed of polystyrene and polyethylene, and the polystyrene/polyethylene component ratio is 90/10 to 25/75 (weight ratio). Its apparent specific gravity is 0.02 to 0.10g/ ^cm3 , and it is usually
A 20% compressive stress of 5 to 10 Kg/cm ² in an impact test at a speed of 5 mph at room temperature (23°C), an energy absorption efficiency of 65% or more, and a load recovery rate of 40% or more.
Lightweight and superior impact performance using expanded plastic foam with a temperature multiplier of less than 2.0 when tested at 5 mph impact speeds at low temperatures (-20°C) and high temperatures (60°C). The present invention is characterized by providing a bumper system with energy absorption performance. Hereinafter, specific features of the present invention will be further explained in sequence with reference to embodiments shown in the accompanying drawings. FIG. 4 is a perspective view showing an example of the structure of the impact energy absorbing bumper 1 according to the present invention. Reference numeral 2 denotes a back-up beam for reinforcement in the bumper, which has a protruding substrate 3 in the center. An impact energy absorbing foam 4 in the form of an elongated block is disposed on the front surface of the backup beam 2, and an outer skin 5 is further provided on the outer surface of the impact energy absorbing foam 4 to cover it. At the end, a mounting screw 6 is attached to the protruding base plate 3 of the backup beam 2.
Fixed by The outer skin 5 can follow the deformation of the impact energy absorbing foam 4, and is made of synthetic resin or synthetic rubber. For example, an injection molded product of thermoplastic resin is used, but from the viewpoint of moldability, economy, and impact resistance, RIM (Reaction
High-density microcellular molded using the Injection Moiding method. Urethane is preferred. On the other hand, the impact energy absorbing foam 4 is made of foamed plastic containing polystyrene or polyethylene. It is a foam, which is an important feature of the present invention, and has particularly limited physical property values. Foamed plastic consisting of polystyrene and polyethylene. Conventionally, foams with a high expansion ratio (low density) and low compressive stress are mainly used as cushioning materials for packaging, but the 20% compressive stress in the impact test at room temperature (23℃) is 2 to 2. 10Kg/ ^cm2
A foamed plastic with a relatively high modulus. The use of this foam is limited, and the use of this foam as an impact energy absorbing foam for an impact energy absorbing bumper for automobiles has not been known at all. Normally, the maximum load (Fmax) and maximum displacement (Dmax) of a bumper are determined by the body strength of the vehicle to which the bumper is installed, and the front load. End, rear. Damage to the car body may occur due to the shape and structure of the end.
It is limited to below a certain maximum allowable value that does not cause damage. Therefore, making both Fmax and Dmax as small as possible to absorb a certain specified impact energy means that there is no need to increase the vehicle's body strength, and it also reduces the front end, rear, and This is desirable in the sense that it does not limit the design possibilities of the end. The impact energy absorbing bumper of the present invention has a 20% compressive stress of 2 to 10 in an impact test at room temperature (23°C).
Kg/cm ² and has a stress range suitable for a vehicle bumper, and has very high energy absorption efficiency, which means that the bumper's Fmax and
It has the characteristic of keeping Dmax as small as possible within the allowable range for the vehicle. Furthermore, this excellent impact energy absorption performance is also characterized by stability over a wide temperature range and low temperature dependence. Moreover, such an impact energy absorbing bumper can be significantly lighter than conventional technology, and has great industrial advantages in light of the current social situation from the viewpoint of reducing the weight of the vehicle body, improving fuel efficiency, and economical efficiency. . The above-mentioned impact energy absorbing foam has a polystyrene/polyethylene component ratio of 90/10 or more.
It can be obtained by satisfying the following conditions: 25/75 parts by weight and an apparent specific gravity of 0.02 to 0.10 g/cm ³ . Foamed plastics containing polystyrene/polyethylene as impact energy absorbing foams as described above. When using foam, if the apparent specific gravity is less than 0.02g/ ^cm3 , the compressive force will be 20% smaller, and it will be too soft for the purpose of a vehicle bumper, and when a certain impact energy is applied, it will bottom out and the Fmax will be lowered. , Dmax are both too large, and are not suitable for the purpose of the present invention. On the other hand, the apparent specific gravity (density) is 0.10
If it is larger than g/cm ³ , the 20% compressive stress becomes too high, resulting in a disadvantage that Fmax becomes too large. Here, if Fmax becomes too large, it means that it exceeds the vehicle's body strength, resulting in damage to the body. Therefore, when absorbing a given impact energy, Fmax, Dmax
It is preferable to make both of them as small as possible. or,
Foamed plastic made of polystyrene/polyethylene. Foam with 10% polyethylene content
If the polyethylene component is less than 75% by weight, the load recovery rate will be 40% or less, and if the polyethylene component is more than 75% by weight, the temperature multiplier will be 2.0 or more, both of which provide a bumper with excellent impact energy absorption performance that meets the objectives of the present invention. However, it is not suitable for the purpose of the present invention. Note that in this specification, energy absorption efficiency,
The load recovery rate and temperature magnification are defined as follows. Energy Absorption Efficiency Energy absorption efficiency is calculated from the stress-displacement curve upon impact as shown in FIG. 1 using the following equation. Energy absorption efficiency = E / A + E × 100 (%) (However, A and E indicate the area of each part.) Load recovery rate The load recovery rate is the first impact and its 30 minutes as shown in Figure 2. It is calculated from the stress-displacement curve of the subsequent second impact using the following equation. Load recovery rate = E' (2nd impact) / E (1st impact)
×100 (%) (However, E and E' indicate the area of each part.) Temperature multiplier The temperature multiplier is calculated from the stress-displacement curves at -20℃ and 60℃ as shown in Figure 3 using the following formula. It is calculated accordingly. Temperature magnification = E ₁ (-20°C) / E ₂ (60°C) (However, E ₁ and E ₂ indicate the area of each part.) In each of the above cases, E absorbs up to 50% displacement. represents the energy and is equal to the area under the stress-displacement curve up to 50% displacement. Next, a foamed plastic containing the polystyrene/polyethylene as a component according to the present invention. Foam is a copolymer foam obtained by reacting styrene monomer and ethylene monomer so that the polystyrene/polyethylene components have a predetermined component ratio, and is manufactured by fusion molding using expandable beads. It can be easily manufactured by any of the following molding methods: , extrusion molding, and injection molding, but it is preferably manufactured by fusion molding using expandable beads. Fusion molding using expandable beads is performed by pre-foaming particles of a copolymer of styrene and ethylene impregnated with a low boiling point substance such as butane, propane, pentane, or petroleum ether as a blowing agent using steam heating, etc. to produce primary foam beads. This is a known molding method in which the primary foamed beads are dried and matured, then filled into a mold of a desired shape, heated with steam or the like, and subjected to secondary foaming to obtain a foamed product of the desired shape. In addition, as the outer skin made of synthetic resin or synthetic rubber in the present invention, for example, as mentioned above, RIM
High-density microcellular urethane molded by the (Reaction Injection Molding) method is preferably used, but high-density microcellular urethane molded by the RIM method uses a highly reactive liquid raw material, so it is thin-walled and large-sized. It has the advantages of being able to be molded into products and has a fast molding cycle, and the resulting molded product also has excellent mechanical properties, so it has a great effect on damage resistance during impact. It is the most suitable material for the outer skin of vehicle bumpers from both economical and functional perspectives. In this case as well, the molding method and compounding method are known among those skilled in the art and are selected depending on the purpose, but for the purpose of the present invention, the density is preferably 0.9 to 1.15 g/cm ³
Flexural modulus 1000~ according to ASTM D-790-66
A molded piece of 4000Kg/cm ² is selected. Further, the back-up beam 2 in the present invention has the purpose of fixing an outer shell made of synthetic resin or synthetic rubber and an impact energy absorbing foam disposed inside the outer shell in a predetermined position, but the maximum load generated in the event of a collision is Materials with mechanical strength that can withstand
Usually designed as a structure. Next, specific embodiments of the bumper of the present invention including manufacturing thereof will be explained based on Examples.
Of course, these are just a few examples, and it goes without saying that the present invention is not limited to these examples. In addition, the shape of the outer skin made of synthetic resin or synthetic rubber, the shape and arrangement of the impact energy absorbing foam, and the shape of the back-up beam all depend on the design of the vehicle to which the bumper according to the present invention is installed and the required impact energy. Needless to say, it can be selected arbitrarily depending on the absorption performance. Furthermore, in the following examples, the impact test was carried out using a dimension 40
A rectangular parallelepiped impact test sample measuring cm x 10 cm x 10 cm was heated to the specified temperature for 16 to 24 hours, and then immediately cut into a sample having a structure similar to that shown in Figure 4 (40 cm length x 10 cm height x 10 cm width). was mounted on a fixed stand, and an impactor with a weight of 510.3 kg, which had a sufficient area to compress the entire impact surface of the impact test sample, was placed at an impact speed of 5 miles/hour (8.05 km/hour). I set it up and conducted an impact test. Further, the second impact to determine the load recovery rate was performed 30 minutes after the first impact. For the outer skin, 100 parts of polypropylene glycol (EP-240 manufactured by Mitsui Nisso Urethane Co., Ltd.) with an OH value of 25, ethylene. 18 parts glycol, 1 part DABCO 33LV (manufactured by Nippon Nyukazai Co., Ltd.), 0.06 dibutyltin dilaurate
5 parts of Freon-11 (manufactured by Daikin) and a prepolymer derived from diphenylmethane diisocyanate (manufactured by Sumitomo Bayer Urethane) Sumidyur PC, NCO% = 26
%) 106 parts (all parts by weight) were molded using a RIM casting machine with a wall thickness of 3 mm, a density of 1.10 g/cm ³ , and a flexural modulus of 1800 Kg/cm ³ (ASTM D-790-66). Cellular urethane was used for impact testing in the examples described below. Note that the energy absorption efficiency and the load recovery rate temperature magnification were calculated using the respective formulas shown in the definitions above. (Example 1) Density 0.033 obtained by molding by bead method
g/ ^cm3 expanded polystyrene/polyethylene foam (polystyrene/polyethylene component ratio = 75/
25 (weight ratio)) was placed inside the microcellular urethane shell formed by RIM molding as shown in FIG. 4, and an impact test was conducted according to the method described above. As a result, the first
As shown in the table, an impact energy absorbing bumper system was obtained that exhibited excellent energy absorption efficiency and had a temperature multiplier of 1.25 and excellent temperature dependence.

[Table] (Example 2) Density 0.05g/obtained by molding by bead method
cm ³ of expanded polystyrene/polyethylene foam (polystyrene/polyethylene component ratio = 50/50
(weight ratio) was subjected to an impact test in the same manner as in Example 1. As a result, it exhibits excellent energy absorption efficiency at extremely low density as shown in Table 2.
An impact energy absorbing bumper system with a temperature multiplier of 1.72 and excellent temperature dependence was obtained.

[Table] (Comparative Example 1) On the other hand, for comparison, the density was 0.033 using the bead method.
A 100% styrene foam with a weight of 100 g/cm ³ was molded and subjected to an impact test in the same manner as in Example 1. As shown in Table 3, the results showed that the energy absorption efficiency and temperature multiplier were good, but the load recovery rate was low at 34.3%, which could not be said to be sufficient as a bumper system.

[Table] (Comparative Example 2) For comparison, a 100% ethylene foam with a density of 0.056 g/cm ³ obtained by molding by the bead method was subjected to an impact test in the same manner as in Example 1. The results shown in the table are seen, and the temperature (23
The 20% compressive stress at 60°C is as low as 1.72Kg/cm ² , the energy absorption efficiency is low, and the temperature multiplier is 2.22, which means that the temperature dependence is poor, so the maximum stress at 60°C is extremely large. It was a bumper system with

[Table] (Comparative Example 3) Polypropylene with an OH value of 28. Glycol. Acrylonitrile. Steele. Graft copolymer (polymer manufactured by Mitsui Nisso Urethane Co., Ltd. Polyol 34-28)
75 parts, hydroxyl-terminated liquid polybutadiene with an OH value of 45 (Poly bd R-45HT manufactured by Idemitsu Petrochemical Co., Ltd.) 30
sorbitol-derived polyether with an OH value of 488 (PA-14635 manufactured by BASF-WY&D)
15 parts, 1.0 part of water, 1.0 part of triethylenediamine, silicone surfactant (manufactured by Nippon Unicar L-
5303) 1.0 part of liquid diphenylmethane diisocyanate-derived prepolymer (manufactured by Mauvay Chemicals, E-451, NCO%)
27%) 50.9 parts (all parts are by weight),
After stirring evenly, the inner volume is 4000cm ³ (vertical 40cm x horizontal 10
cm×height 10cm) with a density of 0.11g/
cm ³ polyurethane. I got the form. This polyurethane. When the foam was subjected to an impact test in the same manner as in Example 1, the results were as shown in Table 5.

【table】

[Table] As can be seen from Table 5 above, the density is 0.11g/
cm ³ and higher density than the samples in Examples, the 20% compressive stress at 23°C is relatively small, and the maximum stress and maximum displacement are also large. In addition, the energy absorption efficiency was also lower than in Examples, and the temperature multiplier was also large. As described above, the bumper with impact energy absorption characteristics of the present invention has extremely excellent characteristics for use in vehicles, and plays an extremely important role in meeting the needs of society in terms of safety measures, and is expected to have practical effects. It is something that will be done.

[Brief explanation of the drawing]

Figure 1 shows an example of a typical stress-displacement curve during impact.
Figure 2 is an example of a typical stress-displacement curve for the first and second impact, Figure 3 is an example of a typical stress-displacement curve at -20℃ and 60℃, and Figure 4 is a typical example of the stress-displacement curve for the first and second impacts. FIG. 1 is a perspective view of a vehicular impact energy absorbing bumper showing a configuration example of the invention bumper. 1... Impact energy absorbing bumper, 2... Backup beam for reinforcement, 3... Protruding board, 4
... Shock energy absorbing foam, 5 ... Outer skin.

Claims (1)

[Claims] 1. An impact energy absorbing foam is arranged on the front surface of a back-up beam for reinforcing the bumper, and an outer skin made of synthetic resin or synthetic rubber is fixed to the back-up beam so as to cover the foam. In the impact energy absorbing bumper for vehicles, the impact energy absorbing foam is composed of polystyrene and polyethylene, and the polystyrene/polyethylene component ratio is 90/10 to 25/2.
An impact energy absorbing bumper for a vehicle characterized by using expanded plastic foam having an apparent specific gravity of 75 parts by weight from 0.02 to 0.10 g/cm ³ . 2. Expanded plastic foam composed of polystyrene and polyethylene has a 20% compressive stress of 2 to 10 Kg/cm ² and an energy absorption efficiency of 65% in an impact test (speed: 5 miles/hour) at room temperature (23°C). The impact energy for a vehicle according to claim 1, which has a load recovery rate of 40% or more and a temperature multiplier of 2 or less in an impact test at -20°C and 60°C (speed: 5 miles/hour). Absorbent bumper.