Impact energy absorption structure for motor vehicle

Abstract: An impact energy absorption structure for a vehicle, comprises left and right front frames (1) having a closed section; left and right L-shaped stay members (6) connected at their lower ends to the left and right front frames (1), respectively and having left and right upper ends (63) projecting upwardly above the left and right front frames; and a bent member (5) curved convexly in the forward direction of the vehicle and transversely connected at its left and right ends to the left and right upper ends of the frames (1), stays (63), respectively. The impact energy absorption structure is accommodated within a small space between the front bumper and the front end of the front frame and is particularly suitable for vehicles having a short overhanging front section such as one-box cars. As a result, in the event of a minor collision, the impact energy is absorbed by the deformation of the impact energy absorption structure without operating the air bag.

Description: The present invention relates to an impact energy absorption structure for a motor vehicle and particularly to an impact energy absorption structure for absorbing an impact energy when a vehicle has a head-on collision. The body front structure is primarily composed of left and right front frames connected with the inner side of a front wheel apron and having a closed section structure in the longitudinal direction of the vehicle, and a front bumper connected with each front end of the left and right front frames through a bumper stay. When a vehicle equipped with an air bag system has a head-on collision, first the front bumper collapses and then an impact load is transmitted to the left and right front frames respectively through the bumper beam and bumper stays. Then, the impact load is inputted to the left and right frames respectively and the impact energy is absorbed by a buckling deformation of the front frames. An air bag is operated when the impact load is inputted to the front frames. One example of this technology is disclosed in JP-U-6-18165. In the case of a vehicle equipped with an airbag system, it is necessary to adjust the impact sensitivity in order to prevent a crash sensor from sensing an impact in the event of a light collision. For example, in the prior art shown in Fig. 5, the tuning is made by use of a bumper stay connected to the front end of a front frame. That is, when an impact load is inputted, the impact energy is absorbed temporarily by the collapse of the bumper stay. In Fig. 5, "a" denotes a front frame, "b" denotes a front bumper, "c" denotes a bumper beam, "d" denotes a bumper stay, "e" denotes a toe board, "f" denotes a floor tunnel and "g" denotes a crash sensor. Generally, the front frame "a" is connected by butt welding at its rear end with the toe board "e" and the crash sensor "g" is installed at a portion reinforced by a cross member (not shown)in the floor tunnel "f". In this case, a certain length L 1 of crash stroke must be ensured at the front of the front frame "a", however, in case of vehicles having a relatively short overhanging front section like mini-cars and one-box cars it is difficult to establish an appropriate length of crash stroke between the front bumper and the front frame. JP-A-09039696 relates to a fitting structure for front grille guard of vehicle mounted with air bag. The front grille guard is disposed in front of the bumper and is fitted to the side members (left and right front frame) via plate like brackets. At the time of a light collision, the plate like brackets are bent at the bend sections when a main pipe is retreated, the collision is hardly transmitted to the side members. Thus, an object of the present invention is to provide an impact energy absorption structure capable of absorbing an impact force even in a vehicle having a small space for crash stroke between the front bumper and the front end of the front frame when the vehicle has a head-on collision. An impact energy absorption structure for a vehicle comprises: a left and right front frame having a closed section and provided in the longitudinal direction of the vehicle; a left and right L-shaped stay member connected at its lower end to the left and right front frame, respectively, and having a left and right upper end projecting upwardly above the left and right front frames; and a bent member curved convexly in the forward direction of the vehicle and transversely connected at its left and right ends to the left and right upper end respectively of the front frame. Fig. 1a is a top schematic view showing an impact energy absorption structure according to a first embodiment of the present invention; Fig. 1b is a perspective view of an impact energy absorption structure according to a first embodiment of the present invention; Fig. 1c is a side view of an impact energy absorption structure installed on a vehicle; Fig. 1d is a sectional view taken along a line D-D; Fig. 2 is a cross-sectional view showing another variation of an impact energy absorption structure; Fig. 3 is a graphical illustration showing an impact energy absorption characteristic of an impact energy absorption structure; Fig. 4a is a side view of an impact energy absorption structure according to a second embodiment of the present invention; Fig. 4b is a perspective view of an impact energy absorption structure according to a second embodiment of the present invention; Fig. 4c is a cross-sectional view showing a connecting section of a curved member with a stay member; and Fig. 5 is a perspective view showing an example of a prior art impact energy absorption structure. Referring now to Fig. 1, numerals 1, 1 denote the left and right front frames and numeral 2 denotes a front bumper connected with the front end of the left and right front frames 1,1, respectively. The front frame 1 has a closed cross-section, being provided in the longitudinal direction . The front end of the front frame 1 comes near the rear side of the front bumper 2. Numeral 4 denotes an impact energy absorption structure for absorbing the impact in the case of a light collision. The impact absorption structure 4 is constituted by a bent member 5 constituted by a pipe bent convexly in the front direction of the vehicle and left and right stay members 6, 6 connected by welding to the left and right ends of the bent member 5 respectively. The stay member 6 is constituted by a mounting stay 6a which extends longitudinally along the front frame 1 and a rising stay 6b which rises in the forward and oblique direction. The mounting stay 6a and the rising stay 6b are both formed of a pipe. The rising member 6b of the stay member 6 is connected by welding at its upper end to the left and right ends of the bent member 5, respectively. The thus constituted impact energy absorption structure 4 is fastened to the side face of the front frame 1 with bolts and nuts through a bracket 7. Thus, the impact energy absorption structure 4 is mounted across the left and right front frames 1,1 in such a way that the bent member 5 is offset upwardly with respect to the front frame 1, and its forefront portion (the center of the vehicle widthwise) projects in the foreward direction with respect to the front end of the front frame. As a result, the forefront portion of the bent member 5 is close to the back surface of the outer surface of the front bumper 2. The bracket 7 is constituted by a plate 71 connected to the side face of the front frame 1 and a clamp member 72 having a holder section 72a. Therefore, the mounting stay 6a of the stay member 6 is fastened to the side face of the front frame 1 with bolts and nuts being sandwiched between the plate 71 and the clamp member 72. Further, in an example shown in Fig. 1, the plate 71 extends downwards from the front frame 1 and a towing hook 8 is provided at the extended portion of the plate 71. Fig. 2 shows another example of the bracket 7 which is constituted only by a clamp member 72. In this example, the mounting stay 6a is fastened to the side face of the front frame 1 with bolts and nuts being sandwiched between the side face of the front frame 1 and the holder section 72a of the clamp member 72. Also in this case, a towing hook 8 can be provided when extending the bracket 7 downwards. Generally, even in vehicles having a short overhanging front section, like mini-sized cars and one-box cars, a small longitudinal space "L" (for example about 50 millimeters) between the front end of the front frame 1 and the front bumper 2, can be ensured as shown in Fig. 1c. When the vehicle provided with the impact energy absorption structure 4 between the left and right front frames 1, 1 has a light head-on collision, the impact load is transmitted from the front bumper 2 to the forefront portion of the bent member 5 and the bent member 5 is deformed. In this case, the bent member 5 is pushed backwards and is deformed in such a way that the left and right ends of the bent member 5 are expanded laterally. At the same time, the rising stay 6b of the stay member 6 is bent outwardly about the mounting portion by the bracket 7. The resistance force generated when the bent member 5 and the stay member 6 are deformed is established below a value not operating the crash sensor "g" mounted in the center tunnel, and accordingly in the case of a light collision, the absorption of the impact energy is performed within a limit "G" (impact sensing G expressed in gravitational acceleration) for firing the air bag, whereby an erroneous operation of the air bag can be prevented. On the other hand, when the vehicle has a heavy head-on collision, after the impact energy absorption structure 4 has absorbed the impact energy within a specified stroke "L", the impact load is transmitted to the front end of the front frame 1. When the crash sensor detects an impact "G" larger than a limit "G", the air bag is fired and at the same time the impact energy is absorbed by the buckling deformation of the front frame 1. Fig. 3 shows the result of an impact experiment on the impact energy absorption structure according to the first embodiment. In Fig. 3, a hatched area indicates an impact energy absorption zone by the impact absorption structure 4. The barrier load (resistance force) in this zone is smaller than a lowest set value (approximately 5.00 ton·f) of an impact sensing G of the crash sensor. Therefore, the crash sensor does not detect an impact and does not activate the air bag. When the deformation stroke reaches about 50 millimeters, the barrier load is transmitted to the front end of the left and right front frames 1,1 and the resistance force sharply increases. Then, the crash sensor detects an impact G and the air bag is operated. The front frames 1,1 start to undergo a buckling deformation from their front end and absorb impact energy. Thus, in the event of a minor collision, the air bag is not operated, since at the initial stage of impact, the impact energy absorption structure 4 absorbs an impact energy within a crash stroke of approximately 50 millimeters. In the event of a great collision, the peak value of the resistance force of the front frame 1 can be reduced, because the impact energy absorption structure 4 absorbs a substantial amount of the impact energy at the initial stage, and the overall crash stroke can be maintained at the same time. Fig. 4a to Fig. 4c show a second embodiment of the present invention, in which the impact energy absorption structure 4 comprises a bent member 51 for transversely connecting the front ends of the left and right front frames 1,1 and a stay member 61 for connecting the left and right ends of the bent member 51 with the left and right front frames 1, 1. Thus, the bent member 51 is installed between the left and right front frames 1,1 in a state in which it is put on the front bumper 2. In particular, the bent member 51 is formed by a skeleton member 52 made of pipe, bar, square closed section material and the like and by a stress absorption member 53 made of elastic synthetic resin like urethane foam. Further, there are provided mounting bosses 54, 54 for connecting the bent member 51 at the left and right ends of the skeleton member 52 with the left and right stay members 61, 61. The stay member 61 is made of a pipe and comprises a mounting stay 62 extending longitudinally along the front frame 1 and a rising stay 63 rising from the front end of the mounting stay 62, forming an "L" when viewed transversely. The rising stay 63 has a threaded section 64 at its upper end. When the stay member 61 is fastened to the side face of the front frame 1 through the bracket 7 in the same manner as in the first embodiment, the rising stay 63 rises from the front end of the front frame 1 with its upper end projecting above the upper face of the front bumper 2. After that, the bent member 51 is put on the front bumper 2 and the rising stay 63 is fitted at its upper end to the mounting boss 54 of the skeleton member 52. Then, the bent member 51 is screwed to the threaded section 64 of the rising stay 63 with a fastening cap 9. Thus, the bent member 51 is rotatably and removably fixed to the stay member 61. In this state, the forefront portion of the bent member 51 projects the lenght "L" (for example approximately 50 millimeters) in front of the front end of the front frame 1, and the bent member 51 is offset upwardly above the front end of the front frame 1. Although a towing hook 8 is not shown in Fig. 4a, it may be provided when extending the bracket 7 downwards. When the vehicle with the thus constituted impact energy absorption structure, has a minor head-on collision, an impact load is transmitted to the front bumper 2 and almost simultaneously to the forefront portion of the bent member 51. First, the front bumper 2 collapses and then almost at the same time the stress absorption member 53 is elastically deformed. On the other hand, the skeleton member 52 is also simultaneously, deformed. Hence, the impact energy is absorbed through the deformation of these components. The resistance force of the bent member 51 is established to be a lowest set value of the impact sensing G of the crash sensor, whereby the air bag is prevented from being fired unnecessarily. When the vehicle has a great collision to the extent that the bent member 51 is deformed beyond a limit "L" of the deformation stroke, an impact load is transmitted to the front end of the front frame 1 and the crash sensor detects a collision. The thus constituted impact energy absorption structure has an impact absorption characteristic similar to the one shown in Fig. 3. Therefore it has the same operation and effect as the first embodiment. Further, when the vehicle equipped with the impact energy absorption structure shown in Fig. 4 has a minor collision, the stay member 61 is not deformed because the bent member 51 is bent backward and is at the same time rotated around the connecting section with the stay member 61. This results in reduced repair costs. Further, since the bent member 51 is integrally molded with a stress absorption member 53, the bent member 51 itself can constitute a component according to the invention. In the examples shown in the first and second embodiments, the stay members 6 and 61 are mounted on the side face of the front frame 1, and may be mounted on the upper face or the inner face of the front frame 1. Further, the impact energy absorption structure according to the present invention is suitable for mini-size cars or one-box cars having a short overhanging front section. However this impact energy absorption structure can also be applied to vehicles having a relatively long overhanging front section. When the vehicle receives a small impact, the impact energy transmitted to the bent member is absorbed by the deformation of the bent member and the air bag is not operated, as described above, because the bent member of the impact energy absorption structure, according to the present invention, is bent forward and the stay member holds the bent member, and because the bent member projects in the foreward direction of the front frame. When the vehicle receives a great impact, the impact energy is transmitted to the front frame after deformation of the bent member and the crash sensor detects an impact to operate the air bag. The thus constituted impact absorption structure has not only a very simple structure but is also able to prevent an unnecessary operation of the air bag in the event of a minor collision in vehicles having little space between the front bumper and the front end of the front frame.

Claims: An impact energy absorption structure (4) for a vehicle having a front bumper (2), comprising: a left and right front frame (1) having a closed section and provided in the longitudinal direction of said vehicle; a left and right L-shaped stay member (6;61) connected at its lower end (6a;61) to said left and right front frames (1,1), respectively and having a left and right upper end projecting upwardly above said left and right front frames (1,1); and a bent member (5;51) curved convexly in the forward direction of said vehicle and transversely connected at its left and right ends to said left and right upper ends (66;63), respectively. The impact energy absorption structure according to claim 1, wherein said bent member (5) is rigidly connected to said left and right upper ends (6b) of said stay member (6), respectively. The impact energy absorption structure according to claim 1, wherein said bent member (51) is rotatably connected to said left and right upper end (63) of said stay member (61), respectively. The impact energy absorption structure according to claims 1, 2 or 3, wherein said left and right stay member (6;61) is made of a pipe, respectively. The impact energy absorption structure according to claim 1, 2, 3 or 4, wherein said bent member (5) is made of a pipe. The impact energy absorption structure according to any one of claims 1 to 5, wherein said left and right stay members (6;61) are connected longitudinally to said left and right front frame (1,1) through a left and right bracket (7) provided on said left and right front frames (1,1), respectively. The impact energy absorption structure according to any one of claims 1, to 6, wherein said bent member (51) is constituted by a skeleton member (52) curved convexly in the forward direction of said vehicle and by a stress absorption member enclosing said skeleton member (52) therein. The impact energy absorption structure according to claim 7, wherein said skeleton member (52) is made of a pipe, a bar or a square closed section material. The impact energy absorption structure according to claim 7 or 8, wherein said stress absorption member (53) is made of an elastic synthetic resin. The impact energy absorption structure according to claim 6, 7, 8 or 9 wherein said bracket (7) has a towing hook (8) at its extended portion.

Inventors: MIYAJIMA AKIHIRO, OGURI TAKEMI, TAKAHASHI NOBORU, TAWARAYAMA TAKASHI, MIYAJIMA, AKIHIRO, OGURI, TAKEMI, TAKAHASHI, NOBORU, TAWARAYAMA, TAKASHI
Applicants: FUJI HEAVY IND LTD, FUJI JUKOGYO KABUSHIKI KAISHA
Application year: 1998
Main classification: B60R19
IPC codes: B60R19, B60R21, B62D25, B62D21