US 3572465 A
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United States Patent  Inventor William Carl Olson West Sacramento, Calif. [211 App]. No. 535,443  Filed Mar. 18, 1966  Patented Mar. 30, 1971  Assignee Thunder Enterprises West Sacramento, Calif.
 LIQUID SHOCK ATTENUATING AND PREVENTING DEVICE 1 Claim, 5 Drawing Figs.
 US. Cl 188/1, 94/1.5,188/88, 215/52, 220/116, 244/138, 256/13.1,261/116,139, 293/1, 293/62, 293/70, 188/155, 215/99, 261/139, 293/48, 293/60, 293/63, 293/69, 293/71  I Int. C1. ..B60r 19/08, B61f19/04, Fl6d 63/00  Field of Search 94/ 1 .5; 215/52, 99; 220/38.5; 244/138; 256/13.1; 293/1, 60, 62, 63, 69, 70, 71, 48; 293/51 (F), 52 (F), 71 (P); 267/1 16, 139; 215/l.5
 References Cited UNITED STATES PATENTS 193,015 7/1877 McCarthy 220/38.5 876,504 1/1908 Tabler 220/38.5 900,223 10/1908 Smith 215/99X 1,402,324 1/1922 Van Gelder 293/71 1,677,403 7/1928 Morrison 220/38.5X 2,712,913 7/1955 Stanley 244/138 2,730,396 1/1956 Johnson 293/71X 2,731,290 l/1956 Corydon.... 293/71X 2,829,915 4/1958 Claveau 293/63X 2,964,139 12/1960 Wittl et a1. 244/138X 3,140,11 1 7/1964 Dabroski 293/62 1,771,319 7/1930 Schmidt 293/69 1,833,367 11/1931 Moore 293/71 2,194,042 3/1940 Wyatt 293/69X 2,807,899 10/1957 Adams 293/69X 3,284,122 11/1966 Rich 293/1 FOREIGN PATENTS 2,399,829 6/1930 Australia 293/69 Primary Examiner-Arthur L. Lapoint Assistant Examiner-Howard Beltran Attarney-Smyth, Roston & Pavitt ABSTRACT: Impact is attenuated by a hollow resilient elongated one-piece body formed by a substantially flat reinforced rear wall, a top wall and front, side and bottom walls defining a cavity which is filled with water. A plurality of apertures are provided in the top wall, each of which apertures is defined by resilient walls and is closed by a resiliently deformable plug in frictional engagement with the aperture walls. 1n response to a strong impact against the front wall of the body, a series of physical steps occur which result in ejecting the plugs from, followed by water from the cavity upwardly through, the apertures.
Patented March 30, 1971 31 Z0 Plum? 3 m'n/ranc'e v if C20 E P114412 Pirate I LHQUID SHGCK ATTENUATKNG AND PREVENTING DIEVKCE This invention relates to shock attenuating and preventing devices in general, with particular attention being given to such devices as may be adapted for use on, or in connection with, automobiles and are provided to eliminate or reduce the damaging effect of sudden impacts by or against the vehicle.
Commencing very shortly after automobiles were first put on the market and made generally available to the public, and continuing to the present date, there have been patented hundreds of inventions with the object of reducing the damaging effects of automobile collisions, in the form of various types of shock absorbing bumpers. These prior patents appear to fall into one of several categories, namely:
1. Bumpers connected with liquid filled shock absorbing pistons, as for example: U.S. Pat. Nos. 1,702,675 filed Sept. 20, 1928, to G. Ventura; 1,799,894 filed Nov. 17, 1930, to F. Fritsch; 2,187,625 filed Mar. 7, 1936, to J. Mercier; 3,008,746 filed May 27, 1959, to A. C. Senger; 3,139,290 filed Sept. 18, 1961 to C. Swick.
2. Bumpers connected with air filled pistons, as for example: U.S. Pat. Nos. 1,172,001 filed Feb. 15, 1916, to E. A. Baker, et al., 1,373,822 filed Apr. 5, 1921, to Harry A. Kleine; 2,555,436 filed Jun. 5, 1951, to E. F. Druilhet.
3. Bumpers connected with pistons filled with extrudible solids, as for example: U.S. Pat. Nos. 2,997,325 filed Aug. 22, 1961, to G. H. Peterson; 3,097,725 filed Jul. 16, 1963, to G. H. Peterson.
4. Spring type bumpers as for example: U.S. Pat. Nos. 2,997,325 filed Aug. 22, 1961, to G. E. Peterson; 3,097,725 filed Jul. 16, 1963, to G. H. Peterson; 1,402,324 filed Jan. 3, 1922, to H. Van Gelder.
5. Rubber bumpers, as for example: U.S. Pat. Nos. 1,348,030 filed Jun. 12, 1919, to W. J. Millard; 1,744,408 filed Jul. 18, 1929, to W. J. Millard.
6. Resilient hollow bumpers which contain entrapped air or other fluid which may be compressed, as for example: U.S. Pat. Nos. 1,402,324 filed Oct. 13, 1921, to H. Van Gelder; 1,552,965 filed Dec. 1, 1924, to R. L. Smith; 1,724,431 filed Aug. 13, 1929, to C. Spear; 1,727,982 filed Sept. 10, 1929, to A. M. Jacobs; 1,834,824 filed Dec. 1, 1931, to A. B. Brown; 2,144,357 filed Jan. 17, 1939, to L. Y. Booharin; 2,236,507 filed Apr. 1, 1941, to A. F. Kreitz; 2,890,904 filed Jun. 16, 1959, to A. Materi; 3,169,756 filed Feb. 16, 1965, to R. B. Miller; 3,187,710 filed Jun. 8, 1965, to l(. Wilfert; 3,203,723 filed Aug. 31, 1965, to A. Montenare.
7. Resilient hollow bumpers which contain air or other fluid which, upon compression, may escape through an orifice or orifices, as for example: U.S. Pat. Nos. 1,679,782 filed Aug. 7, 1928, to J. W. Postel; 2,681,246 filed Jun. 15, 1954, to J. Corydonll; 2,731,289 filed Jan. 17, 1956, to J. Corydon ll; 2,731,290 filed Jan. 17, 1956, to J. Corydon 11.
Despite the availability of the number .and variety of all these bumper inventions, and despite the crying need for some type of device to reduce the high accident toll which occurs daily on this nations highways, the plain, simple and indisputable fact is that no major car manufacturer in the United States has ever adopted for any of its cars, and continued to equip them with, any of these prior art bumpers.
Recently it has been suggested that a suitable bumper could be made of rubber, plastic or other resilient material in the form of a hollow tube which is filled with water or other fluid and provided with a series of rearwardly directed orifices plugged by corks or other removable stoppers. Means were provided to attach this tube to an existing car bumper. it has been found that when an automobile equipped with such a bumper strikes an object at a speed of a few miles per hours, some shock attenuation is attained as a portion of the water is driven through the orifices and out of the resilient tubular element.
The present invention is directed to providing an efficient and practical bumper of the type last described, which can eliminate the most serious effects of collisions at speeds up to at least 30 m.p.h., but which can readily be manufactured economically and formed in an aesthetically pleasing design such that car owners would not object to having them incorporated into their vehicles.
The main cause for damage and injuries in a collision, or any other kind of impact results from the fact that upon impact of an object the frontal surface portion engaging the hindrance is rather instantly immobilized, while the center of gravity of the object continues to move. The bulk of the kinetic energy of the object must be dissipated while its front is already positively position locked'against the hindrance. This is particularly prevalent in case of any metal-to-metal or comparable type impact the occurrence of which must be avoided. In particular, it must be avoided that the front of the frame of a vehicle locks into an immobile position just milliseconds or less after having travelled at a high speed and while the bulk of the vehicle continues to move. The resulting impact shock can be avoided if the front part of the frame of the vehicle is decelerated without hindrance-to-frame-position-lock, but at a rate not materially different from the deceleration of the center of gravity of the vehicle.
When a water-filled flexible bumper of the type contem plated presently is disposed in such a manner as to receive the full force of impact between an automobile and some other objects, at a collision speed of 5 miles per hour or greater, the flexible bumper will ordinarily be deformed, but the impact of the front of the flexible bumper results in no appreciable impact shock for the vehicle. As deformation occurs, the water in the bumper will be subject to such an amount of compression that the vehicle decelerates; also, several or all of the stoppers will be forced out of the orifices, and water is jetted out of the thus plugged orifices at a rate in proportion to the intensity of the impact speed.
From an examination at slow speeds of motion pictures taken of collisions in which bumpers of the type herein contemplated have been employed, 1 have observed that the bumper operates to attenuate or even prevent the shock of impact in a plurality of phases, as follows: There is an initial, partial crushing of the flexible bumper during which the vehicle is slowed down by losing kinetic energy utilized in building up pressure in the bumper. Soon certain or all of the plugs or stoppers are popped out and jets of water will be observed to rise out of the unplugged orifices. As this occurs, the vehicle will temporarily be decelerated only slightly, but soon again the height of the water jets begins to decrease due to the decompression of the water still in the bumper and resulting from the production of the initial high jet. The forward inertia of the vehicle again takes over to produce a second crushing of the bumper shell resulting in another compression phase followed by the ejection of additional quantities of water through unplugged apertures. Again there may be a noticeable relaxing as a point is reached where the water is decompressed due to the jetting out water. Additional sequences of the same character may be observed depending upon the speed of impact, the quantity of water in the bumper, and the number and size of the orifices through which the water is jetted out.
i have found that this alternating sequence of compression and decompression, i.e., of deceleration at high and low rates provides for a deceleration of the occupants of the car with complete safety for a wide range of impact speeds, and practically without impact shock if, upon complete crushing of the bumper shell, the vehicle has in fact stopped.
in view of this sequential action, 1 have found that for most effective impact shock prevention, the bumper should be so designed that approximately 50 percent of the volume of the water contained between the collapsing forward wall and parallel rear wall of the bumper may be ejected during a period of from 15 to 20 milliseconds following impact. Unless such percentage of the thus contained water body may be ejected from the orifices prior to completion of deceleration, any cushioning or other impact-force-preventing action, occasioned by the water ejection will not attain the optimum effect to stop the vehicle at about the instant when the frame position locks against the crushed bumper, then sandwiched between frame and hindrance.
In order to accomplish the evacuation of such proportion of the liquid within such a short time span there must be taken into account the number, size and disposition of the orifices, the viscosity of the liquid, the volume thereof, and pressure developed in the liquid. For these aspects the alternation between phases of deceleration and water ejection is rather essential.
With respect to the number of orifices or apertures and their disposition, it is my observation that these should desirably be disposed over substantially the entire length of the hollow bumper in order to provide the greatest range of speeds at which shock may be substantially prevented, and preferably not more than 6 inches apart. As to the size of each orifice, I have found that an approximately 1% to l /diameter aperture permits the evacuation of a sufficient volume of water with the pressure buildup which is found to occur upon collision.
In the device of the present invention, the orifices are directed upwardly so that as the water is driven therethrough upon the application of shock and pressure caused by impact, to the contained liquid, a significant portion of the kinetic energy of the vehicle is actually dissipated away from the hindrance as well as the automobile frame. The acceleration of the water occurs vertically and upwardly, i.e., in a direction substantially at right angles to the forces acting on the frame of the vehicle. To accomplish such deflection of the kinetic energy out of the system most effectively, the orifices should be located on top of the hollow elastic member and toward the rear wall thereof. This location of these orifices is also advantageous in that deformation of the member upon impact will last affect the plugged apertures. If the apertures are located toward the leading (or contrasting) edge of the hollow member, it might be possible for initial deformation of the upper transverse wall actually to prevent the release of the stoppers or plugs.
The stoppers or plugs should be frictionally engaged in the apertures such that all of them do not readily pop out with the first small pressure buildup. Thus in a collision at a slow rate of speed, as for example, m.p.h., only a few of the stoppers may be popped out. On the other hand, at a speed of 25 mph all stoppers will be blown out instantly. To provide for such frictional engagement, the upper transverse wall in which the apertures are located may preferably be molded with cylindrical plug seats.
Alternatively, the resilient shell may be so formed that, upon deformation and/or the application of pressure, certain preselected areas of the upper transverse wall yieldingly open up to permit water jets to be driven therethrough.
With respect to the liquid itself, I have found that water is the best for a number of reasons: In the first place, it is plentiful and costs practically nothing in most civilized areas of the world. Secondly, it is of such viscosity that it can be most rapidly evacuated from the hollow shell through the orifices upon impact. While gasoline is of similar viscosity, one obviously would not wish to eject gasoline into the air at the time of a collision. Further, while water will freeze at 32 F this freezing point may readily be dropped by the addition to the water of modest quantities of sodium chloride. Were oils or glycerin to be employed, they would not only be more expensive, but, aside from the problem of requiring much larger apertures to evacuate the hollow bumper in the quantity required prior to milliseconds after impact because of their viscosity, the highway authorities would not welcome such liquids being sprayed over any portion of the road where the collision occurs. In addition, thecars involved in the collision would have to be thoroughly scrubbed to remove the oil or glycerin. Water is, therefore, the most practical and economical liquid for use in the impact attenuating devices of the present invention.
As to the volume and shaping of the hollow bumper shell itself, 1 have found that vertical depth of the contained water need be no greater than 4 or 5 inches, and 1 inch of water, measured on the horizontal will enable the bumper to prevent shock developed by impact of an automobile at an approximate speed of 5 mph Thus, with approximately 5 inches of water disposed on the horizontal at a 4 to 5 inch depth, the bumper should readily decelerate a car travelling at 25 mph. which collides with another parked vehicle, or with another vehicle travelling in the opposite direction at a similar speed and being likewise equipped with such a bumper.
The bumper shell itself must be specially constructed to withstand the shock and pressures which are developed upon impact and not to rupture upon the occurrence of the same.
Otherwise, the liquid contained in the shell may be completely evacuated prior to the critical instants of time mentioned above. This can be established by placing the orifices in a plane that includes the direction of impact, i.e., in the horizontal, as then the orifices or apertures can be deformed prior to opening to provide for a safety-type escape nozzle preventing the buildup of excessive pressures prior to actual popping of stoppers.
Previous bumpers of this type which I have observed before my invention have been made of two pieces of polyethylene joined together by heat sealing together the edges of the two separately molded pieces. Upon impact, the sealed edges rupture and thereby permit uncontrolled evacuation of the contained liquid, with consequent diminution of the attenuating effect of the bumper. The present invention, therefore, contemplates the molding of the shell of the shock attenuating device in one piece and with no sealing, preferably using polyurethane, in a slush-molding process. By this technique a single piece shell may be created which resists rupture by the tremendous force and pressure developed by the main crash pulse. Polyurethane is preferred not only because of its great strength, but also because it is abrasive-resistant and has the ability to withstand the effects of sunlight and cold temperatures which adversely affect rubber, polyethylene and vinyl.
By the use of the slush-molding process, as herein disclosed, the bumper may be constructed in a curved-end or wraparound shapes, thereby better to protect the ends of the vehicle incase it should be involved in an angular collision. This process further has the advantage of enabling the manufacturer to produce the shells at a rapid rate, i.e., in less than 1 minute each.
The forward or leading edge of the bumper and the upper and lower horizontal connecting walls should have a wall thickness of 35 thousands to 50 thousands of an inch. The rear wall, however, is of special construction. Because high decelerating pressure is built up in the bumper during crushing but before any relief is obtained by the popping out of the plugs and creation of water jets through the apertures or orifices, the rear wall must be heavily reinforced and stiffened against collapse. in the preferred embodiment of my improved shock attenuating device, the rear wall is not only molded to a thickness of approximately 1 to lkinches, but it is molded about a stiffening plate of metal, or preferably a pair of channel members which extend substantially the entire length of the rear wall. In addition, it should include a recessed area to accommodate the cars license plates, and may even be molded to receive some type of light to illuminate the license plate as required by certain state laws, and directional lights, such as are used on most late model cars.
While the specification concludes with the claim particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawing in which:
FIG. 1 is a top view of a bumper in accordance with the preferred embodiment of the present invention;
FIG. 2 is a sectional view taken along lines 2-2 in H6. 1;
FIG. 3 is a perspective view of a car with a bumper shown in F268. 3 and 2;
Fit}. d shows the preferred configuration of a stopper and orifice or opening in the bumper, and in sectional view; and
FIG. 5 illustrates somewhat schematically the several phases of the crushing of the bumper during an impact.
Proceeding now to the detailed description of the drawings, there is shown a frame pertaining to the undercarriage of a motor vehicle and having side rails 12 and 13 interconnected by a crossbar l1 and extending towards the rear of the vehicle. A bumper which is the subject of the present invention is mounted to the frame 10 by means of Lshaped brackets 16. There are two brackets each for respectively mounting the bumper in a horizontal position to the rails 12 and 13. The body of the bumper extends in front of the ends of rails 12 and 3.3, and the outer rear wall of the bumper is preferably in engagement with these rail ends.
A reinforcing strut 17 extends at angles from the rear center of the bumpertowards the two side rails, and the bumper is mounted to the strut by two additional brackets 16. Any force exerted upon the rear wall of the bumper is thus distributed to act on therails l2 and 13 permitting additionally some elastic deformation of the strut 17.
The bumper 20 is comprised of a plastic, one-piece shell 21 made of polyurethane and having a more or less flat top 22, a contoured front portion or front wall portion 23 the configuration of which being to some extent a matter of styling and design. However, the projecting front 230 performs an impor tant function in that it defines a rather large distance from the rear wall 24, such as for example, 13 inches. The front wall of the bumper may be about 35/ 1000 of an inch thick.
The bumper defines a cavity 25 having a volume to hold a sufficient amount of water, which, for the average passenger car, may be of the order of 10 gallons; The rear wall 24 includes two steel channel members 26 and 27. The member 26 has a flat U-shaped cross section, and member 27 has a groove 27a. The members 26 and 27 are welded together, first by welding the member 27 to the legs of the U of member 26, and additionally, the groove 27a is welded to the bottom of the U of member 26.
The cavities thus formed in between members 26 and 27 receives the heads of bolts 1% by means of which the bumper is mounted to the brackets 16 which are, in turn, secured to the frame parts 12, 13 and 17. The reenforcing structure 2627 is embedded in the rear wall 24 of the bumper shell, i.e., it is covered with the same plastic of which the remainder of the bumper is comprised. Additionally, the cavities defined by the members 26 and 27 may be filled with plastic, partially or completely. However, it has been found that the degree of filling of these cavities is not critical. The reenforced rear wall of the bumper suffices to take up any pressure developed in the bumper without lasting deformation. The two-piece structure of this reenforcement drastically improves the resistantweight ratio of the structure.
The top' wall 22 of the bumper is provided with a row of holes or apertures 30 which extend crosswise and are disposed toward the rear of the bumper. These holes or apertures communicate with the interior 25 of the bumper and, preferably, have cylindrical shape about 1% inch in diameter. The apertures normally receive stoppers 31 which are retained in the cylindrical holes by friction. The stoppers 31 have a conical configuration and the wider diameter portion is near the head 32 thereof, normally having a diameter larger than the diameter of the respective holes 30, so that the stoppers 31 can be wedged into the holes. As will be developed more fully below, the number of stoppers removed during an impact depends on the impact speed. it follows, that the number of apertures is a, to some extent, matter of choice. The stoppers are hollow to form a cavity, so that the head 32 is quite thin. Should the pressure in cavity 25 be rather high, the head 32 will bulge upwardly, thus narrowing the configuration of the stopper in the plane of the opening, thereby (l) overcoming the frictional retaining force and (2) producing a gap between the wall of an aperture 30 and the body of the stopper.
A tall 33 is integral with and extends from the inner center of head 32 into the interior of the bumper. The tail 33 terminates in means provided for purposes of restricting the upward movement of the stopper. Thev end of the tail may be connected to a restraining cross such as 34 having dimensions prohibiting passage through an aperture 30. Alternatively, all the tails of the several stoppers may be interconnected by a rope in cavity 25, so that the stoppers mutually prevent their escape.
The bumper may further be provided with holes 36 which actually are deformations of the wall structure and do not communicate with the interior 25 of the bumper. Since for some or many car models turn signals are mounted in the plane of the bumper and are flush with the front surface of the bumper, these holes 36 are provided for receiving these turn signals. The bumper may be constructed with wraparound ends 29 which are actually part of the styling and serve primarily to fashion this bumper after the configuration and shape of the conventional, solid metal bumper. However, these wraparound ends may prevent some shock or damage from angular collisions.
Before developing the phases of operation of the bumper as disclosed, during an impact, some consideration will be given to the requirements, and subsequently it shall be discussed how the bumper as disclosed meets these requirements.
As was mentioned above, studies have been made regarding vehicles having a conventional bumper, and forces were measured as they were developed in various parts of the vehicle and in various portions of the bodies of occupants during and immediately subsequent to an impact.
Almost without exception, very small, if any, forces were measured within the first 20 to 25 milliseconds after impact for speeds between 28 and 35 m.p.h. at impact. In particular,
impact is defined here as the instant of first contact of the foremost portion of the vehicle with a nonyielding barrier. This foremost portion is usually the bumper or a portion of the bumper.
The results obtained generally verify what was suspected all along, that the conventional bumper is little more than a piece of trimming which just is crushed and collapses during and immediately following impact without offering any material resistance and thus without imparting any effective deceleration to the vehicle. One can see that at a speed of 35 m.p.h. a car travels about 1 foot in 20 milliseconds and this is about the same time the car was found to travel after impact without material impediment, i.e., without actually impacting and without being seriously subjected to slowdown. One foot is approximately the dimension of the weak forestructure of the vehicle, and until this weak forestructure is compacted to become sandwiched in between the frame of the vehicle and the hindrance, there was no real impact.
As the front portion of the frame becomes, so to speak, locked against the hindrance, the impact proper occurs and the center of gravity of the vehicle will then begin to decelerate; but it can do so only by dissipating its kinetic energy in that it performs work in the form of bending and lifting the frame and the remaining structure of the car. The body of the car, in general, will follow the slowdown of the frame to the extent of a firm connection to the frame.
Safety aspects usually are concerned only with the effect an impact has on the occupants, and effects on the vehicle are of interest primarily to the extent that forces are transmitted by and through the vehicle to the occupants. What are the causes of injuries? To begin with, it must be observed, that upon impact of a car against a nonyielding barrier, the front of the frame end is locked into an immobile position rather instantly. This actually is the definition of an impact and occurs when the front end of the frame becomes immobilized. in a steel-tosteel impact any displacement will be very small and the front end will be slowed down in a period of time as it takes the front end of the frame to stop while traversing, say a few millimeters. There will thus occur instantaneous deceleration rates in the neighborhood of 10 g., or above, depending on the speed at such an impact.
The remainder of the vehicle will slow down at a rate as permitted by the resiliency of the cars frame. Since, however, the line of impact will not run straight through the center of gravity, a torque will be developed. The bending of frame parts, elastic deformation thereof and pivoting of the car, i.e., lifting of the rear end thereof, all enlarge the stopping distances for the several parts, so that the actual rate of deceleration of these parts will be lower because here deceleration is spread over some longer periods of time. The development of strong torques bending the frame or parts, is primarily the result of the rather instant slow down of the front of the frame part of the vehicle, because the position locking of the frame at its front end prior to dissipation of kinetic energy of the vehicle as a whole sets up a torque, with the reaction occuring against the hindrance as a stationary fulcrum point. Any kinetic energy, not dissipated as bending and/or lifting work, will be stored as elastic energy in the frame, and will after impact, actually propel the car in the opposite direction.
Damage to the occupants of a vehicle is due primarily to the fact that the pivot motion of the rear end of the car lifts the oc cupants upward, while their unimpeded inertia propels them in forward direction, so that they are actually catapulted out of their seats. The recoiling of the vehicle due to expansion of the compressed vehicle increases the relative movement between vehicle and occupants. The body or parts of the body of an occupant are individually stopped by impact upon parts of the car. It is not so much the average deceleration of his body, or parts of his body which causes the injuries to the occupant, decisive is the fact that stopping of the body or of parts of body occurs also by an impact, resulting in rather instant stopping of the skin tissue. The remainder of the body part is stopped by compression due to frontal transmission of the stopping force, compression which may have very little damping effect and impacting bones are crushed accordingly.
Unless extremely tight, seatbelts will not prevent but merely restrict the propulsion or catapulting of the person out of the pivoted seat. Moreover, the belt again operates as a frontal restrainer of the passenger. If the seatbelt is anchored to a portion of frame which has slowed down rather rapidly, possibly at 10 g., a very high deceleration will occur on all parts of the body in direct engagement with the seatbelt, directly and frontally. Due to the pivot motion of the rear of the car the occupant is catapulted upwardly and forwardly out of his seat and into direct frontal engagement with the seatbelt, be it a shoulder or a hip belt. Depending on the degree of resiliency, this impacting on the seatbelt can also cause great injuries. The catapulting is actually even more prevalent in case brakes were applied, because a strong torque is set up as between the rearwardly directed tangential braking forces transmitted through the wheels, and the forwardly directed inertia referenced against the center of gravity.
Thus, the principal objective of the inventive bumper is the prevention of a front lock of the frame of the vehicle against a relatively immobile object when the vehicle is otherwise still in motion while simultaneously preventing resilient recoiling so that the car will not be propelled backwards.
Consider now what happens if a hollow bumper is used which is filled with a fluid but there is no escape provided for the fluid. This would amount to a complete omission of the orifices 30 in the bumper illustrated. At impact the front wall -of the bumper locks onto the hindrance while the rear wall continues to move with the vehicle. This means that the fluid will be compressed rather rapidly, and due to the fact that water when used as a liquid, is regarded as highly incompressible, the pressure developed to counteract reduction in volume sets up to the forces which slowdown the vehicle at a rather steep and increasing rate again so that in fact an extreme steep deceleration is developed, as the bumper may be compressed only for a few inches.
Assuming that the bumper shell would not rupture, the vehicle would be stopped long before the front wall of the bumper touches the rear wall of the bumper with extremely high pressure being developed inside of the bumper. Moreover, excessively compressed water takes on the characteristics of a solid. Most of the energy would be reversibly stored in the liquid thus compressed, and will be released as an accelerating force which propels the vehicle in backward direction. This means that there would be a very small stopping distance, quite comparable with an actual impact, and the same short distance is available for a very strong reverse acceleration of the expanding bumper.
One can readily seethat the situation is similar only if a very small aperture would provide for some escape in the bumper. A highly restrictive orifice cannot materially improve the very limited cushioning effect of a completely closed and water filled bumper.
The other extreme case is a bumper having very large openings, or openings directed in downward direction. In this case the fluid is discharged very rapidly, without exerting any cushioning effect on the vehicle. In other words, the vehicle would simply shift the liquid out of the bumper as it contracts the volume of the bumper. Such shifting requires little energy and thus there would be no deceleration or practically no deceleration; the final impact would be quite similar to that occurring with a regular all metal bumper.
Having the foregoing in mind, we turn now to the specific objective of the bumper which is the subject of the present invention. It is desired to induce slowdown of the rear wall of the bumper which is firmly attached to the front end of the frame, at a rate such that the vehicle is stopped when the rear wall of the bumper engages the front wall thereof to lock the vehicle to the hindrance, so that there is no impact at all, except for the front wall of the bumper. For a speed at impact of about 35 m.p.h. and, say a foot bumper thickness, as stated above, complete deceleration should occur within 1 foot producing an average deceleration of about 40 g. of the rear wall of the bumper lasting for about 40 milliseconds, to be compared with an initial shock of possibly 1,500 g. if this rear wall would impact directly at full speed on the immobile hindrance. This deceleration acts on the frame as a whole, without locking of the front part of the frame into an immobile position, so that a fulcrum point is not established nor, for all practical purposes, will there be a resilient compression of the frame structure as 40 g. straight deceleration has no structural consequence on a steel bar.
However, impact can be avoided only, if the kinetic energy of the vehicle can be dissipated during the period the bumper is, compressed. Since the frame is not to impact, no point thereof can serve as a fulcrum. Thus, no torque is set up as between the inertia force of the decelerating vehicle and a reaction between vehicle front and the stationary hindrance. Therefore, the occupants are not propelled in upward direction. The special problem resulting from the likely application of brakes will be dealt with separately.
Since the occupants remain in frictional contact with their seats, which are always rearwardly inclined in downward direction, any horizontal deceleration force exerted upon an occupant increases his frictional engagement with the seat. Thus, his inertia works against the friction and the springs of the seat, without the aid of seatbelts. It follows, that without impact the occupants are decelerated primarily by tangentially effective forces, and by resilient reaction of the springs in the seat. It follows further, that as long as the friction suffices that it cannot be overcome by the inertia of the occupant, he will not even be pushed against the seatbelt, let alone crash against the dashboard. This can be accomplished by providing for a nonuniform deceleration of the vehicle.
We proceed next to a description of the phases of operation of the bumper (FIG. 5). At the moment of impact, in most instances though not necessarily, the front point 23a of the bumper will strike the hindrance 40 first. The frame does not impact at all at this instant. We need to concern ourselves only with the worst case condition in which the hindrance absolutely does not yield, suchas a concrete wall, the bumper of a truck travelling in opposite direction, etc. Since the bumper of the present invention is made of resilient plastic naturally there will be no deformation of the hindrance, but at the first impact the front wall portion 23a of the bumper comes to a complete stop rather instantly, producing two effects:
This first impact on a limited portion of the bumper shell operates as a limited size source for production of a shock wave in the bumper shell itself which shock wave is trans mitted as such through the bumper shell'and into the vehicle, also as a shock wave, and without exerting material slowdown effects upon the vehicle. Moreover, this wave is materially attenuated by the material of the bumper, and the water contacting the shell dampens this shock wave materially.
The second effect is that a shock wave is produced in the water. This shock wave is specifically the result of the fact that the bumper material and the liquid near the area 23a travel at first with the vehicle but are brought abruptly to a halt, building up the pressure in the adjacent liquid which will propagate as a pressure wave in all directions and at the speed of sound in the water, and this speed, of course, is much faster than the speed of the vehicle.
The first shock wave travelsthrough the water towards the rear wall of the bumper and through the bumper shell and into the vehicle. As the shock wave in the water hits the rear wall of the bumper, there will be no concentrated impact, because the wave propagates in all directions. Thus, very little energy is transmitted upon the vehicle, having practically no slow down effect.
It must be observed that the first impact is not a one-time blow on a restricted area. As the vehicle continues to travel the area of impacting widens due to the projecting structure 230. Thus, the area of shock wave production increases in time, and shock waves will be produced consecutively from all points along the front wall of the bumper whenever a particular portion of this front wall 23 comes to a halt. It follows that a whole series of shock waves will be produced crisscrossing through the'liquid in the bumper.
As stated above, some energy will be dissipated. It is basically the kinetic energy from the front wall of the bumper and of the liquid in the front portion in the bumper which is so dissipated. For the vehicle as a whole, this is of very little con-' sequence.
p) builds up rather gradually, i.e., with a low dp/dt, and from there it further follows that db/dt is low which in turn means: no actual impact whatever when slow down begins. It should be noted, that hereinafter we shall speak of an impact only to describe the first contact of the bumper shell with the hindrance, which is no impact at all as far as the frame of the vehicle is concerned. The pressure buildup is actually induced by the elastic deformation of the bumper reducing its volume. This pressure acts in all directions, and is operative as reaction force against the hindrance as well as against the vehicle. If the hindrance is a mobile object, it may be moved. However, the discussion is centered on a worst case condition which is a nonyielding-immobile object. Thus, deceleration force against the vehicle is built up as the pressure increases. in particular the reenfo'rced rear wallstructure transmits the pressure frontally upon the frame rails 12 and 13 and. that decelerates the vehicle as a whole. Moreover, the strut inhibits yielding of the center of the rear wall of the bumper.
During phase 'two" the shock waves together with a continued compression of the bumper shell will deform side and top walls of the bumper shell' which becomes effective as deformation of the apertures 30. Due to the crisscrossing of the bumper shock waves, this deformation is variable in degree and depends on time of occurrence in relation to the time of the first bumper impact. This deformation is highly irregular as far as the several apertures 30 is concerned, Moreover, the increasing pressure inside of the bumper shell will deform the stoppers in that the heads 32 will begin to bulge outwardly thus contracting the stopper.
It will be observed that the deformation will depend on the size of the shell apertures and on the elastic properties of the Phase two actually overlaps phase orie," and is characterized by the fact that immediately following impact of the resilient front wall of the bumper there will begin a reduction in volume of the interior of the bumper as a whole. The resulting compression will spread throughout the bumper but not as a usual compression wave which is followed always by a decompression wave. The reduction in volume of the bumper compresses the water, and this pressure increase propagates throughout the water in the bumper at the speed of sound in the water, reaching all portions of the liquid and raising the static pressure thereof and, to some extent, the temperature as well. This pressure increase propagates through the liquid in that it follows the initial shock wave.
Thus, during phase two" the slowdown of the vehicle begins, because the building up of pressure in the water in cavity 25 requires energy to be taken from the kinetic energy of the vehicle. As the result of the initial contraction of the interior of the bumper the liquid is compressed. The liquid analogy to Hookes Law sets forth the equation dP=dVI V. k
with P being the pressure in the liquid, Y being the volume 6? the bumper and lg being the constant of compressibility, having for water a value at room temperatures of approximately 5Xl0 in CGS units.
The deceleration b of the vehicle having mass M, thus follows Newtons law in that the force M-b is equal to the pressure (above atmospheric pressure) in the bumper, multiplied by the effective area Q of transmittal, which is the area of the rear wall of the bumper. Thus M-b=p'Q. The pressure as it is built up isfdv/Vle, orfl Q(t)-v/VZ dz, with 1/ being the speed of the vehicle and Q(t) the area of contact of the bumper with the hindrance. One can readily see here, that the pointed configuration of the bumper produces a very small area Q(t) at first, and Q(t) increases as the vehicle progresses and squeezes stoppers and of the bumper. The deformation will further depend on the speed of the vehicle, as this speed determines the speed or rate with which the pressure is caused to increase. Thus, sometime after impact of the front of the bumper, and this is now the phase three" of the operation, some of the apertures and stoppers will deform to such an extent, that at least a portion of the wall of one or more stoppers disengages from the aperture. The degree of this deformation will again depend on the speed of the vehicle and the other factors mentioned above. How many of these apertures will reach a material degree of deformation will also depend on the speed of the vehicle. There will always be a first one among the several stopper-aperture assemblies, but others will soon be deformed likewise to produce this gap and the rate at which the gaps are produced again is dependent upon the speed of the vehicle at impact.
As small openings are formed in between stoppers and the wall defining the respective orifices, one, or a few, very small escape or relief nozzles are formed. There is a delay (phase two") of at most a few milliseconds between the first impact and the formation of a nozzle of this type which means that,
for such a short initial period, there is a rather rapid buildup of pressure in the shell; any further pressure increase is then checked and relieved by a high powered jet or jets escaping through such nozzles formed by deformed stopper-aperture assemblies. This has been observed as a fine, rapidly developing jet which checks the pressure buildup in the bumper.
As stated, the size of this deformation aperture is dependent upon the speed of impact. Prior to the formation of the escape nozzles the speed of the vehicle at impact determines the rate: of pressure increase exclusively in accordance with Hooks' formula given above. After an escape nozzle has been formed,-
speed. Nevertheless, compression still prevails over any pres-' sure relief, so that the pressure continues to be increased in all.
the bumper and at a rate, still dependent on the speed of impact. But this rate of pressure increase is less than would occur without the escape provided by the deformed stoppers aperture assemblies. Thus, as the deceleration increases rather steeply during phase two, it will tend to level off in phase three." This is in accordance with the desired objective, because the deceleration must not become excessive, as it will become if the water should be compressed to an extent to become comparable with a solid body.
The high powered jet in addition sets up a decompression wave which reforms the arrangement of those stopper-apertures not yet deformed to an extent that a nozzle outlet has been created. The decompression resulting from the initial jet or jets checks the buildup of too great a pressure in the bumper, thus preventing rupture of the shell until one or several stoppers have been lifted substantially.
The steep rate of deceleration as imparted upon the vehicle is effective only for a few milliseconds, slowing down the vehicle drastically, but without any impact whatever. An occupant is in frictional contact with his seat and cannot be pushed out of his seat upwardly, as there is no torque developed with reference to a stationary fulcrum point. The occupant will thus not be pivoted and catapulted out of his seat. Due to the backward inclination, the frictional contact with the seat is actually increased, impeding further tangentially directed from shifting the occupant out of the seat.
The head and shoulders of an occupant will tend to continue at the original speed due to the first law of Newton, but these body parts are also slowed-down, without impact, merely by transmission of the retarding force acting tangentially from the seat throughout the body on the sitting occupant, and acting as well on his shoes. The retardation is additionally damped, i.e., extended in time as to effectiveness due to elastic yielding of the seat.
Up to this point, only a few milliseconds have elapsed since the initial contact of the bumper front with the hindrance, but slowdown of the vehicle has begun at a high rate but without impact upon the frame. Depending upon the degree of deformation of stoppers and apertures and depending further upon the speed of compression, high pressure has been built up in the bumper, and phase four will begin. This latter phase involves ejecting the several stoppers out of the orifice in which they are respectively secured. I
The changeover from phase three to phase four is a gradual one and actually begins when, after the very first jet, liquid is set in motion throughout the bumper towards those stoppers having yielded to produce a jet. Since compression has continued, the stoppers will begin to move in upward direction; not all of them, as some are being held back. This holding back will increase as the first stopper actually begins to move even very slightly out of its normal position.
It will be appreciated that at an impact speed, of say mph. of a medium size vehicle, all or substantially all of the stoppers will begin to recede from the respective apertures, as they are all being deformed practically simultaneously. The available forces are sufiicient to remove them, and none of them will be sucked back into a tightly closing position and reformed. At a low rate of speed at impact, only one or a few of the stoppers will be removed or tend to be loosened as the deformation of stoppers and apertures is strongly consecutively. The deforming forces will act on all of them, but the nonhomogeniety of the pressure, due to shock waves, the crisscrossing of the shock waves, the developing of a decompression wave pursuant to one initial jet in the most deformed stopper hole, and the slower rate of pressure built up, all operate in such a manner that only one or a few stoppers will actually begin to lift. The decompression and suction forces resulting from the beginning flow of the liquid will then act on all others as restraining forces.
As some or all of the stoppers begin to lift, water in the vicinity of the lifting stopper will be accelerated very strongly and in upward direction, and a strong decompression wave is set up for sucking back into locking position all those stoppers which have not been loosened sufficiently. it is quite apparent that this phenomenon is highly speed dependent as, at low speeds, the suction will prevail over the ejecting forces, while, at high speeds, the ejecting forces will be considerably stronger and all of the stoppers will lift.
The initial ejection of at least one of the stoppers can be regarded as the beginning of phase four. Water will rush towards the opening thus provided and decompression throughout will begin. Depending upon the pressure reached during phase three, one or more columns of water will be ejected in upward direction and at high speed. The velocity of these water columns and, thus, the amount of water ejected is proportionate to root of the pressure differential in accordance with Bernoulli and Bunsens Law.
The peak pressure, reached at the end of phase three," is as stated, highly dependent upon speed, and that peak pressure determines the driving pressure differential and thus the speed and the amount of water permitted to escape, first through the jets, and later through the unplugged orifices 30. The water, as it is set in motion throughout the bumper, likewise will have a speed that depends upon the peak-pressure reached during phase three. It follows from Bemoullis law that this flow of water in the shell reduces the hydrostatic pressure therein. The amount of water ejected per unit time, and the thus resulting pressure drop, depends directly on the effective area of the apertures. Such area is determined by the number of stoppers lifted, as well as by the diameter of the apertures from which the stoppers are lifted. Due to the dependency on impact speed of the number of apertures opened, the pressure drop resulting from water ejection is likewise depending upon the impact speed of the vehicle, such speed, however, has already been reduced considerably during phase three.
We, thus now have these effective components: (A) The internal compression prior to opening of the aperture causes ejection of the water columns and thus reduces the amount of water in the bumper. (B) The flow of water causes decompression. (8') At very high impact speeds, say 40 mph. and above, there may not be an effective decompression but merely a reduction in the increase in the continued compression due to the fact that of course the vehicle continues to cornpress the bumper.
(C) The water is ejected in upward direction during phase four. (D) Kinetic energy of the vehicle has been stored as pressure in the bumper during phases two and three." Some of this pressure will be converted into thermal energy, but the bulk will be reconverted into kinetic energy of the liquid during phase four, and again into potential energy as the liquid is accelerated against the force of gravity. The liquid thus performs work by lifting. This is exceedingly important as any water can be ejected at all arid only to the extent the pressure differential against the environment suffices to lift water against gravity.
The rate of decompression, or of the reduction of compression, depends on the overall effective aperture area which includes the degree of lifting of the stoppers at any instant. Decompression is determined further by the number of stoppers lifted, and by the water velocity in the bumper which in turn depends on the peak pressure reached during phase three." As the bumper is decompressed, the decelerating force acting against the progressing vehicle is drastically, and thus slowdown of the vehicle is reduced during phase four. This is also very important as now there is temporary relief with regard to the deceleration imparted upon the occupants.
The first period of deceleration of the vehicle during phases two" and three is very brief, beginning even with a rather smooth gradient due to the bumper peak 23a, and this graduatecl pressure increase will not sufiice to disengage the occupants from their seats, even though such deceleration rate may do so if it were to persist over a longer period. The now operating relaxation during phase four" reduces the tangential surface force acting on the occupants so that the prior deceleration can .become fully effective throughout their bodies thus being operative in toto at a lower rate than the deceleration of the vehicle during phases two and three. Moreover, the frictional engagement of the occupants with their seats is reinforced.
Still during this period of decompression and of relaxing of the deceleration, the outflow of water and thus the separation of mass from the moving system shifts the center of gravity of the vehicle in the direction opposite to its motion. This counteracts any tendency for the setting up of any torque, and should a torque commence to build up during phase three, the shifting of the center of gravity reverses to some extent this buildup, to ensure that there will be no catapulting of the occupants out of their seats. Moreover, the relaxation of the deceleration during phase four expands the springs of the seat again and this also counteracts any torque acting on the seat.
This aspectis very important because it is to be expected that the driver will begin to brake the vehicle when he realizes the approaching hindrance. This by itself sets up a tilting force for the vehicle and may have begun to lift the passengers somewhat out of their seats. The shifting of the center of gravity occurs at the same rate as the outflow of water and is effective as a counter torque in phase four.
Before discussing phase five as it is desired to be carried out, we should consider these extreme cases already mentioned above, but now to be discussed in relation to this particular bumper as used. If the apertures are too small, the deformation of the bumper may actually squeeze the stoppers into a more locking engagement, and only little water escapes through the deformed stopper-aperture system; there would be little decompression and thus the above-described relaxing effect would be little, if at all effective.
Even if some or even all such stoppers should lift, there will be a rather low particular impact speed for which compression continues due to vehicular motion. This is true for all respective higher speeds. Therefore, strong deceleration continues and the pressure may even increase further in spite of the ejection of the water. Thus, there would be too much resilient reaction, even at low speeds, negating considerably the cushioning effective contemplated to be performed by this bumper. If, on the other hand, the apertures were rather large, decompression would be high and the concurrent continued reduction in volume of the bumper due to continued motion of the vehicle will, for even rather high speeds, merely cause the water to flow out at a low pressure in the bumper, exerting no cushioning effect at all onto the vehicle, i.e., there would be now only very little further deceleration leading inevitably to an impact after complete crushing of the bumper.
Recapitulating the conditions set, it is desired to have a definite period of decompression, but one which is only temporary, so that pressure can build up again to slow the vehicle down further.
As the water is ejected it reduces the static pressure in the bumper considerably, so that the kinetic energy used, first to build up the pressure, is dissipated out of the system. There is thus a definite sequencing of deceleration by pressurizing the bumper followed by dissipation of the stored elastic energy as kinetic energy of the jetted water. The moving vehicle continues the bumper compression and, thus, pressure can again build up provided the apertures are not too large, but provided also, that the outflow reduces temporarily, for stopping or at least slowing flow motion of the water in the bumper. [t has been observed actually, that the vertically directed water outflow may actually cease temporarily since water has a definite inertia, and since any flow of water in the bumper in vertical direction is subject to viscous friction a definite pause is established before any outflow, once having ceased can be resumed. Thus, during this pause pressure can in fact begin to build up again, and this is the result of the rapid decompression and flow retardation by gravity and friction.
For any location of the apertures other than on top of the bumper, water outflow will continue merely by virtue of the continued movement of the vehicle. Moreover, the size of the orifices is such that for the speed dependent number that was opened, water would continue to flow out, with little or no throttling provided against the motion of the vehicle, if the water would just be shifted out laterally. The vertical direction of outflow interrupts the outflow appreciably so that compression can occur again.
it has been found that upwardly directed apertures of IVs diameter permit at least one additional phase pressure buildup for a wide range of original impact speeds. it is important that the apertures are directed in upward direction for other reasons; the water jets should neither operate as a propulsion counteracting the deceleration, nor should the jets be directed to strike the vehicle. A vertical ejection of water satisfies both conditions. Also, the vertical water column, as ejected, exerts again static pressure onto the water in the bumper due to the weight which at first counteracts decompression, but as the water jet decays, the drop in pressure thereafter occurs at a rather steep rate. The drop of the hydrostatic in the bumper, due to ejection combined with the force of gravity operates positively as a retardation of continued outflow.
The termination of water outflow is a condition that the water can be compressed again and, to a substantial degree, to provide for another phase of deceleration. Only when the out? flow does practically cease will it be possible for the still moving vehicle to provide for another appreciable compression operative as deceleration force, which is needed, because the deceleration during phases two and three will and should not cause the vehicle to stop, as this would require too much deceleration during that period. Thus, the vertical orientation of theapertures ensures a sequencing of alternating phases: compression-decompression, or, storage of energy in the bumper dissipation of energy or deceleration relaxation. The commencing second compression phase terminates phase four and phase five begins. The vehicle will still travel fast enough to permit buildup again of pressure, so that during the now beginning phase five, and for a wide range of original vehicle speeds, the pressure is built up beyond that what would be sufficient to just pour water out through the opening. Thus, the openings again provide a throttling effect; here then there is a second phase of deceleration.
At first, the pressure built up will prevail, setting the liquid again into motion and into motion and again high columns of water are ejected. The vehicle is slowed down as before now during the second phase of compression, and again there will be strong ejection of water at first, followed by a second period of relaxation as phase six. For the normal case, the vehicle will now come to a stop, as during phase six," the front wall of the bumper contacts the rear wall.
The two extreme cases with regard to aperture size and location now appear in this manner: The smaller the apertures, the shorter will be phase four, and the lower will be the speed, for which little or even no decompression may occur. The larger the apertures, or in case of rearwardly or downwardly directed apertures, the longer will be phase four. Phase five may even occur only for very high impact speeds with no cushioning for lower speeds.
To achieve the inventive objective, it is necessary that there be definite phases four, five and six" in the speed range between 5 to 35 mph, in order to alternate between several periods of strong deceleration and of relaxation. Due to the fact, that the effective overall aperture of water outflow is dependent upon speed, this alternating of phases occurs over a wider range of speeds for upwardly directed apertures of the size stated. However, the size is not so critical and does not require narrow tolerances, but upward direction of the water is most important. Moreover, optimum conditions will vary with the type, i.e., weight (mass) of the vehicle, while an upward direction of the ejected water ensures for all vehicles that the period of relaxation, (phase four") terminates to yield to a definite phase five of compression and deceleration.
The rate of deceleration during phases two," three and five is in proportion to the pressure peaks permitted to be built up in the bumper, At high speeds with almost all or all stoppers removed, the pressure reduction in phase six may well be followed by another brief period of pressure increase. it will be appreciated that even for high original impact speeds say 30 to 40 m.p.h. the vehicle can be brought to a stop when the front wall of the bumper engages the rear wall thereof. At still higher original speeds of the vehicle some impact of the front of the frame and of the rear wall of the bumper against the locked front wall becomes unavoidable. However, regardless of the initial impact speed there will be a considerable speed reduction even in case of front end collisions of two high speed cars before final impact after complete crushing of the bumper. Moreover, the final impact will be plastic against plastic.
The invention has been described with respect to a front bumper. It is readily apparent, however, that the same protection can be provided for the rear of the car. If two cars collide, each one being equipped with a bumper constructed in accordance with the present invention, the effect is doubled. This is particularly noteworthy because after initial bumperto-bumper impact, the slowdown for each car is substantially the same as if the car had hit a stationary hindrance and there is little exchange of momentum as either car dissipates its kinetic energy by jet ejection. Thus, the rule that the impact is doubled if two similar cars have a front collision at similar speeds, will not hold true anymore. Any exchange in momentum is effective by imparting energy upon the water in the bumper of the respective other car, and not on the frame thereof.
It will be appreciated further, that bumpers of this type as described can be used as barrier guards along highways, at sharp curves, etc. The cushioning will be precisely the same if a car which is not equipped with such a bumper hits the bumper pertaining to such guards.
The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be covered by the following claim.
1. An impact attenuating device for disposition in association with a first object over an area thereof which may collide with a second object of substantial mass in a direction of im pact, the device comprising an elongated, hollow one-piece resilient body having a substantially flat rear wall, a top wall and front, side and bottom walls defining an elongated cavity, the cavity filled with water, the rear wall being reinforced by an elongated, rigid member to be secured to the first object, the improvement comprising:
the top wall of the body having portions thereof, extending parallel to said direction of impact and defining a plurality of upwardly directed apertures having deformable sidewalls that extend transversely to said top wall portions;
a plurality of hollow, resiliently deformable plugs closing said apertures when inserted respectively in said apertures, the plugs each having sidewalls and top wall, the sidewalls of the plugs respectively extending in abutment with and in frictional engagement with the sidewalls of the apertures, the plugs adapted for lifting vertically from the respective apertures;
so that upon impact of said second object against the front wall of the body at a speed in excess of several miles per hour and in said impact direction, transverse to the direction of plug lifting, the aperture sidewalls are being deformed, and the differential water pressure in the cavity is increased to reinforce the frictional engagement of the sidewalls of the plugs by the respective sidewalls of the apertures, thereby temporarily retaining the plugs in the apertures and delaying opening thereof for obtaining further pressure increase of the water in the cavity;
said delay of plug ejection concurring with relative deformation as between the sidewalls of at least one plug and the sidewall of the respective aperture receiving the plug to obtain at least one orifice opening between the sidewalls of the one plug and the respective aperture for passing a spray of water to effect pressure relief, prior to lifting of the plug; and
upon further pressure increase a number of the plugs are