WO2005090822A1

WO2005090822A1 - Shock-absorbing device comprising a plastically-deformable member, which is intended, for example, for transport vehicles

Info

Publication number: WO2005090822A1
Application number: PCT/FR2005/000391
Authority: WO
Inventors: Akrum Abdul-Latif; Rachid Baleh
Original assignee: Iut De Tremblay En France
Priority date: 2004-02-18
Filing date: 2005-02-18
Publication date: 2005-09-29
Also published as: FR2866399A1

Abstract

The invention relates to a shock-absorbing device (1) comprising a crushable tube (14) which is installed in a cylindrical body (10) having helical grooves (25) on the walls thereof. According to the invention, the means for crushing the tube comprises a crosspiece (12) and the ends thereof are engaged with the aforementioned helical grooves, such that the tube is subjected to both axial compression and torsion. The inventive device can be used for any application requiring the absorption of kinetic energy in the event of an impact, such as in road or railway transport vehicles or suspended transport vehicles.

Description

SHOCK ABSORBER WITH PLASTICALLY DEFORMABLE MEMBER, ESPECIALLY FOR TRANSPORT VEHICLES

The present invention relates to the field of shock absorbing devices with a plastically deformable member. Such shock absorbers are used in particular for transport vehicles. In the state of the art, kinetic energy absorption systems, or shock absorbers, which comprise at least one member adapted to absorb energy by plastic deformation in the event of impact, are known. For example, for the protection of the occupants of a motor vehicle, there is known a shock absorber constituted by a deformable member plastically interposed between the cross member, bumper side, and the corresponding spar of the vehicle. The absorption member is generally a solid body, relatively short, and more particularly a thin-walled cylinder. This cylinder is shaped so as to be crushed axially in the event of a vehicle collision. Due to the stability of the average crushing load as well as the importance of the crushing stroke per unit of mass, such cylinders are very attractive absorption members. However, their behavior during the crushing process is difficult to predict. The plastic deformation of the wall of the tube can be done according to an axisymmetric mode known under the name of "concertina" mode or according to a non-axisymmetric mode known under the name of "diamond" mode. At the present time, all the parameters making it possible to determine the particular mode of deformation which will occur for a given shape of tube and material are not known. The ratio between the mean diameter of the tube and the thickness of its wall, known as the parameter η, gives an indication of this deformation mode: when η <15, the concertina deformation mode becomes predominant for the majority of metallic materials used in industry; for larger values of this ratio, diamond mode tends to occur. Due to the uncertainties about the crushing behavior of known shock absorbers, it is very difficult to model the behavior of the vehicle in the event of an impact as a function of speed. Furthermore, for applications requiring the absorption of a large amount of kinetic energy, for example in the case of trains and more specifically of high-speed trains, the size of the absorption member becomes too large. . The object of the present invention is to provide a kinetic energy absorption system which makes it possible in particular to solve the above problems. The invention relates to a damping device of the type comprising a deformable member absorbing by plastic deformation of kinetic energy during a stress on said device, characterized in that said deformable member is associated with a transmission member adapted so that, when of said biasing of said device, said deformable member is biased both in axial compression and in torsion. For a given crushing stroke, the imposition of a torsion associated with compression gives a better energy absorption capacity. According to a preferred embodiment, said transmission member comprises means for crushing said deformable member adapted to receive an axial compression load, said crushing means being associated with a helical guide means so as to urge said deformable member to both in axial compression and in torsion. The crushing means is in slide-helical connection with the guide means. The slope angle of the helical guide means determines the speed of torsional deformation for a given crushing stroke. Preferably, said transmission member comprises a cylindrical body on the walls of which are formed helical grooves forming guide means, said crushing means comprising a spider whose ends are engaged with said helical grooves. According to a preferred embodiment, one end of said deformable means is fixed to said crushing means by a first fixing means and the other end of said deformable means is held stationary by a second fixing means. According to an advantageous variant, said first and second attachment means are adhesion attachment means. The blocking results from a clamping force caused, for example by pliers acting on conical half-shells which press the members to be fixed against each other. Such a system allows a solid fixation of the deformable member whatever its section and without influence on its behavior during the crushing. Advantageously, said deformable member is a thin-walled cylinder. Due to the design of the guide means, these cylinders can have all kinds of sections, shapes and initial lengths. All types of metallic materials, composites and polymers can be used apart from fragile materials. The stress exerted on the damping device is, of course, generally a stress of an instantaneous nature such as a shock, but it can also be a stress of a progressive nature. A kinetic energy absorbing system according to the invention has a relatively low cost, a relatively small footprint and it is easy to adapt to a given use. It can find application for all types of transport vehicles like cars, boats, planes, etc. It is particularly interesting in the field of train transport where the shocks suffered are almost always frontal shocks. The incorporation of absorption members according to the invention can be done easily, for example at the level of the coupling systems. High speed trains (TGV) for which the kinetic energy to be absorbed is particularly high are particularly concerned by the present invention. Another field of application is that of suspended means of transport, such as elevators, cable cars or the like, in which the invention can serve as a shock absorber in the event of an accidental fall. The damping device can be installed in a lower part of the suspended means of transport, between a base and a passenger compartment in which there are people to be protected. It can be used in any device requiring absorption of kinetic energy, including in the field of research, in particular as regards the study of the plastic behavior of different materials. The system described makes it possible to apply compression and torsion simultaneously. Alternatively, the torsion may only be applied after a certain crushing stroke.

One can provide for this grooves which are rectilinear and parallel to the axis of the cylindrical body in a first portion of the system. This arrangement is particularly advantageous for an experimental device intended to study the behavior of tubular structures subjected to compression-torsion crushing. The invention will be better understood on reading the appended drawings, corresponding to a nonlimiting embodiment, where: FIG. 1 represents a schematic elevation view of a damping device according to the invention; - Figure 2 is a histogram showing the energy absorbed as a function of the crushing stroke for a device according to the invention and a device according to the prior art; and - Figures 3 and 4 are curves representing the applied load and the energy absorbed as a function of the crushing stroke for two devices according to the invention and a device according to the prior art. The damping device 1 according to the embodiment described generally comprises a deformable member constituted by a tube to be crushed 14 and a transmission member. The tube to be crushed 14 is a thin-walled cylinder of any cross-section, shape and length. It can be made of all types of metallic materials, composites and polymers, apart from fragile materials. The transmission member comprises a hollow cylindrical body 10 of hardened steel on which are machined four diametrically opposite helical grooves 25. These grooves are characterized by a determined helix angle. In this hollow cylindrical body can move a crushing means 12 comprising a cross associated with a disc 16. The ends of the cross 12 are engaged with said helical grooves so that the crushing means is in slide-helical connection with the body 10. On the spider 12 can be applied, via a receiving disc 21, a crushing load. An intermediate cylinder 20 intervenes between the receiving disc 21 and the spider 12. Due to the slide-helical connection of the cross with the cylindrical body 10, a uniaxial stress is transformed into bi-axial torsional compression stress. In order to reduce the friction between the brace 12 and the walls of the grooves 25, the ends of the brace are equipped with bronze rollers 13 adapted to roll in the grooves. The crusher tube 14 is installed in the hollow cylindrical body, between a fixed disc 17 pinned on a base disc 15 installed at the end of the cylindrical body 10 opposite the load and the disc 16 screwed on the spider 12. Systems fixing 30 and 31 of the tube 14 to the discs 17 and 16 respectively consist of clamps 18 associated with conical half-shells 19. A screw allows the clamping of the clamps against the half-shells with the inclined surfaces of which they are in contact, so that the tube is locked against the disc. The assembly and disassembly of the tubes to be crushed 14 is simple. It nevertheless allows a solid fixing without risk of sliding of the tube to be crushed. The method of fixing chosen does not influence the behavior of the tubes during crushing. The tubes to be crushed do not have to undergo any heat treatment or special machining, apart from a simple dressing which makes it possible to adjust their initial lengths to the desired dimensions. The system does not require regular lubrication or special maintenance. The discs can be interchangeable to allow the use of different tube sections. The system described makes it possible to apply compression and torsion simultaneously. Alternatively, the torsion may only be applied after a certain crushing stroke.

One can provide for this grooves which are rectilinear in a first portion of the system. The last two arrangements described (interchangeability of the discs and deferred application of torsion) are particularly interesting for an experimental device intended to study the behavior of tubular structures subjected to compression-torsion crushing such as that which will now be described. The behavior of tubular structures subjected to compression-torsion crushing is studied with a view to optimizing the energy dissipating capacities of a system according to the invention. The device 1 according to the invention is associated with a charging means. The system makes it possible to work in quasi-static mode (stress provided by a press) or dynamic (stress provided by the fall of a body). The effect of the radial (η, ratio between the mean cylinder diameter and wall thickness) and longitudinal (λ, ratio between the mean cylinder diameter and its initial length). The influence of the speed of deformation is also taken into account. For this, we have studied three cylindrical bodies 1 whose grooves have respective helix angles of 30, 37.5 and 45 degrees, so as to work with three different torsional speeds. A first series of experimental tests made it possible to validate the capacity of a device according to the invention to optimize the dissipation of energy by plastic deformation of tubular copper structures. The tubes used are of circular section, with a parameter η of 15 and a parameter λ of 0.075, corresponding to a diameter of 30 mm, a thickness of 1 mm and an initial length of 200 mm. The tests are carried out in biaxial stress out of phase, that is to say that the application of the torsion is deferred beyond the zone of entry into plasticity of the material. In other words, initially, the compression acts alone over a certain axial distance. Figures 3 and 4 show the applied load as a function of the axial displacement, Figure 3 for a loading speed of Imm / min and a propeller tilt angle of 30 ° and Figure 4 for a loading speed of 500 mm / min and a helix tilt angle of 45 °. Each of these figures also shows the applied load-axial displacement curve for an identical tube, but which is simply compressed as in the prior art. If we consider for example Figure 2, we first notice an increase for the device according to the invention of more than 2kN of the average load while the maximum load remains unchanged. In addition, the amplitude of the oscillations beyond the first elasticity peak is much higher for the present invention, which proves that the material is more stressed. The deformation mode is practically axisymmetric (concertina mode), while for the device of the prior art, it is mixed (partially concertina and partially diamond. The figure also shows the amount of energy absorbed as a function of the crushed length for the device according to the invention and for the device of the prior art. The absorption is identical for the first 20 millimeters. Beyond this point, the curve corresponding to the device according to the present invention moves away towards the top as soon as the torsion takes effect. For example, for a crushing of 80 mm, the energies absorbed are 1.59 kJ for the device according to the invention (with grooves inclined at 30 °) and 1.29 kJ for the corresponding device of the prior art. The same observation can be made for the test represented in FIG. 3. The histogram of FIG. 2 represents the energy absorbed by the device according to the invention (out of phase with an angle of inclination of the grooves of 30 °) compared to the prior art device for three crushing strokes (20, 50 and 80 mm) for a stressing speed of 1 mm / min. The energy gain absorbed is a direct function of the torsion occurring in parallel with the compression. For crushings of 20, 50 and 80 mm, the energy savings absorbed are 2%, 18% and 25% respectively.

Claims

1 - Damping device (1) of the type comprising a deformable member (14) absorbing kinetic energy by plastic deformation when said device is stressed, characterized in that said deformable member is associated with a transmission member (10, 12) adapted so that, during said stress on said device, said deformable member is stressed both in axial compression and in torsion.

2 - Damping device according to claim 1, characterized in that said transmission member (10, 12) comprises a crushing means (12) of said deformable member adapted to receive an axial compression load, said crushing means being associated to a helical guide means (25) so as to urge said deformable member both in axial compression and in torsion. 3 - Damping device according to claim 2, characterized in that said helical guide means (25) has a slope angle determined by a chosen twist speed. 4 - Damping device according to claim 2 or 3, characterized in that said transmission member (10, 12) comprises a cylindrical body (10) on the walls of which are formed helical grooves (25) forming guide means, said means crush comprising a spider (12) whose ends are engaged with said helical grooves.

5 - Damping device according to claim 4, characterized in that the ends of said spider (12) are equipped with rollers (13) adapted to roll in said grooves (25).

6 - Damping device according to any one of claims 2 to 5, characterized in that said helical guide means is preceded by a guide means in axial translation.

7 - Damping device according to any one of claims 2 to 6, characterized in that one end of said deformable means (14) is fixed to said crushing means (12) by a first fixing means (31) and the another end of said deformable means is held stationary by a second fixing means (30).

8 - Damping device according to claim 7, characterized in that said first (31) and second (30) fixing means are fixing means by adhesion.

9 - Damping device according to any one of the preceding claims, characterized in that said deformable member (14) is a thin-walled cylinder. 10 - Damping device according to claim 9, characterized in that the section of said cylinder is circular, square, triangular or hexagonal.

11 - Road transport vehicle, characterized in that a damping device according to any one of the preceding claims is interposed between a cross member, bumper side, and a corresponding spar of said vehicle. 12 - Railway transport vehicle, characterized in that a damping device according to any one of claims 1 to 10 is installed at the level of coupling systems.

13 - Suspended transport vehicle, characterized in that a damping device according to any one of claims 1 to 10 is installed at a lower part of said vehicle.

14 - Device for studying the plastic behavior of different materials, characterized in that it comprises a damping device according to any one of claims 1 to 10.