GB1572736A

GB1572736A - Shock-absorbing device

Info

Publication number: GB1572736A
Application number: GB140877A
Authority: GB
Original assignee: Paulstra SNC
Current assignee: Paulstra SNC
Priority date: 1976-01-27
Filing date: 1977-01-13
Publication date: 1980-08-06
Also published as: DE2702373A1; JPS5293877A; FR2339784A1; FR2339784B1

Description

(54) SHOCK-ABSORBING DEVICE (71) We, PAULSTRA S.A. a French Body Corporate, of 61 Avenue Marius Aufan, 92305- Levallois-Perret, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a shockabsorbing device, inter alia for absorbing impact energy (the latter term not being used in a restricted sense and being applicable inter alia to vibrations). The invention finds particular application in vehicle bumpers.

An object of the invention is to increase the absorption possibilities of these devices.

Accordingly, the present invention provides a shock-absorbing device made of elastomeric material and of unitary construction, the device comprising two boundary walls interconnected by a network of walls to define a cellular structure having cells in the form of hollow prisms with their axes parallel to the boundary walls and with a polygonal cross-section, the cellular structure including: a first group of cells arranged in series transversely of the boundary walls and composed of at least two cells each having the same polygonal cross-section; and a second group of cells arranged in series transversely of the boundary walls and disposed adjacent to the first group of cells, the second group of cells being composed of at least one major cell having a cross-section of given polygonal shape and of two minor cells having a crosssectional shape corresponding to part of the given plyogonal shape.

In a shock-absorbing device embodying the invention, shocks are absorbed mainly by resilient buckling of the cells of the cellular structure. If the curve of the forces applied at each instant to the vehicle or structure bearing the device is drawn in dependence on the deformation of the elastomer, the curve has a plateau corresponding to the energy of the absorbed impact. During this plateau, the forces remain almost constant. Consequently, the invention ensures that, at a given impact energy (corresponding e.g. to a limiting speed of a vehicle), the force applied thereto will not exceed a dangerous limit.

The cells of the first group may have the same cross-sectional shape as the or each major cell of the second group, which preferably have a hexagonal cross-sectional shape.

The cells may be substantially open at their axial ends so that air can escape during deformation resulting from energy absorption.

Means for facilitating buckling, such as beads on some of the cell walls, may be provided to facilitate deformation of the cellular structure by resilient buckling of the cell walls.

The walls of at least some of the cells adjacent each boundary wall may be of reduced thickness compared to the walls of the other cells, the reduced thickness cell walls being for example, from 50%to 75%, of the thickness of the other cell walls. In an embodiment of the device, the walls of the minor cells of the second group cells are the reduced thickness walls.

The thickness of the cell walls may be of the order of a quarter of the length of the sides of the cell cross-section.

In a bumper embodying the invention, the boundary walls are elongate and the axes of the cells extend transversely of the length of the boundary walls.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of part of a vehicle provided with bumpers embodying the invention; Figures 2 and 3 are diagrams, in horizontal projection and end view respectively, of a bumper component embodying the invention; Figures 4 and 5 are diagrams in section showing two successive phases in the deformation, under an impact, of a cellular elastomeric device of the kind shown in Figure 2; Figures 6 and 7 are two graphs illustrating the operation of such a device; Figure 8 diagrammatically illustrates a number of modifications which may be made to such a device, so as to vary the deformation properties during buckling; and Figures 9 and 10 illustrate, in the same manner as Figure 2, two other embodiments of a cellular device according to the invention.

Referring to Figures 1 to 5 of the drawings, each bumper device 3 shown therein comprises an elastomeric cellular structure in the form of a network of walls interconnecting a front boundary wall 5 and a rear boundary wall 6 to define a cellular structure having major cells 1 and minor cells 2. The cells are constituted as hollow relatively thin-walled prisms having their axes parallel to the boundary walls, with certain of the cell walls being disposed parallel to the boundary walls and the remaining cell walls extending obliquely with respect to the said certain cell walls. The boundary walls 5 and 6 are elongate and the axes of the cells extend at right angles to the length of the boundary walls.

The cells have a polygonal horizontal cross-section, a hexagonal cross-section in the case of the major cells 1, and are arranged in at least two rows in the direction of the depthp (Figure 2) so that, in successive transverse regions such as A, B, A, etc., each region A contains a first group of two serially arranged major cells 1 and each region B contains a second group of serially arranged cells composed of a major cell 1 between two minor cells 2. The minor cells 2 have a crosssectional shape corresponding to half the cross-sectional shape of a major cell 1.

The rear boundary wall 6 can be secured to a holder 7 (or 71, Figure 9) for securing the device 3 to the vehicle chassis 4 (Figure 1) with the walls 5 and 6 and the axes of the cells disposed vertically. The axes of the cells thus extend at right angles to the direction of the forces to be absorbed which in the case of a bumper, usually act horizontally.

The dimensions of the assembly, i.e. the depth p and the height h of the cells and the wall thickness e, may advantageously be chosen in dependence on the desired absoption curve and the amount of energy to be absorbed. Advantageously, the wall thickness e may be made less for the minor cells 2 than for the major cells 1, as shown ate1 in Figure 2.

By way of example only, two bumpers mounted at the front of a private vehicle and made of elastomer, e.g. polyurethane having a Shore hardness of 50 to 60D, were given the following dimensions, the imposed condition being that the vehicle should without damage withstand an impact at a speed of the order of 8 to 10 km/h.

Length L of each component (in the case of two components); of the order of 650 mm.

Width d of the cell sides: approximately 50 mm.

Horizontal depth p of bumper: approximately 180 mm Height h of cells: approximately 120 mm Wall thickness e: approximately 12 mm Minimum wall thickness e1: approximately 8 mm It can be seen that, in this example, the maximum thickness e is about a quarter of the width of the sides, although this is by way of example only.

The minimum thickness el is usually of the order of 50 to 75% of the maximum thicknesse, although this is not critical. The operation of the resulting bumper is clear from the curves in Figures 6 and 7, in which the abscissa OX indicates the bumper deformation and the ordinate indicates the forces absorbed by the holder of the bumper or bumpers, i.e. by the vehicle.

The absorption of an impact comprises an initial elastic phase during which the assembly retains its overall cellular shape. This phase corresponds to a very steep, substantially straight curve OM. Advantageously curve OM is as steep as possible, in view of the special construction of the cellular unit.

The deformation occuring in this first phase is illustrated in Figure 4, in the transition from the thin line to the thicker line.

In the case of relatively strong impacts, the first phase is followed by a resilient buckling phase, illustrated in Figure 5, i.e. a deformation of the structure by modification of the shape of the cell walls. The nodes rotate around the cell axes and the walls are bent into a curve, as shown in the drawing.

The buckling corresponds to the flattening of the curve at MN (Figures 6 and 7), i.e. a plateau, after which the curve rises again at NNP as a result of a final flattening and compression of the cellular structure.

Plateau MN can vary according to the dimensions of the cell walls (i.e. their length, number, height, thickness and shape), and optimum dimensions for the desired purpose can be chosen by experience. Figure 6 shows a slightly descending plateau, but advantageously the plateau is made parallel to OX, as shown in Figure 7, since it is known that the area beneath the plateau, as shaded at OMNN of Figure 6, represents the impact energy at which the force applied to the vehicle or structure remains substantially constant. If the area is large, the vehicle can absorb correspondingly greater impacts without damage.

The inclined portion MN (Figure 6) corresponds to a special case only; the cells can be dimensioned so that portion MN is substantially parallel to the OX axis, as shown in Figure 7 at MN or MINI.

Figure 8 is a diagrammatic illustration of various means of improving the curve and increasing the plateau and thus increasing the buckling possibilities. As can be seen from Figure 8, the following, inter alia, can be varied: The thickness of some walls, as shown at 13 where one wall has been made thinner, The shape of the walls, as diagrammatically illustrated at 14 where a bead facilitating buckling has been provided, or at 15 where the wall is curved or, The wall inclination, as shown at 16 in Figure 8.

Of course, Figure 8 is diagrammatic only and is adapted to illustrate various features which can be used separately.

Figure 9 shows a more concrete embodiment comprising beads 14. The set of bumpers is protected at the front by a protective metal frame 51, the rear holder on the vehicle having the reference 71.

Figure 9 also illustrates the provision of holes 17 at the cell nodes, so as to increase their deformability.

These various additional means of facilitating buckling can be used to obtain deformation due to buckling over a considerable proportion of the depth of the elastomeric unit. For example the deformation Ox (Figure 7) will be approximately 0.4p in the case of a unit as described in Figure 2, but can be increased to 0.6 p or more by using means such as shown inter alia on Figure 9.

OMNP represents the curve obtained for a unit of the kind in Figure 2, whereas the curve becomes OM1N1P when the unit is formed as in Figure 9 or in similar manner.

The hexagonal shape is no way indispensable, as shown by the variant in Figure 10, in which the cross-section of the cells 1 of the first group is pentagonal, some pentagon apices being disposed on bases 5 and 7.

The cells are open at their ends, so that air is not compressed during deformation. However, there is no reason against providing elastomeric or other covers for at least partly closing the cells at the aforementioned ends.

There is no reason, incidentally, against partly compressing the air in the cells.

Instead of extending at right angles to the length of the device, i.e. vertically when applied to bumpers, the cells can extend in the longitudinal direction, i.e. horizontally in the present application, or may even extend obliquely.

The application to bumpers, which has been described more specifically hereinbefore, is the most promising since all the impact energy can be absorbed in a relatively small volume, in the case of impacts at low speed and a given maximum absorbed force, without causing any damage to the vehicle However, this application is by no means the only possible application.

More particularly, shock-absorbing devices according to the invention are of value in all cases in which it is necessary to absorb not only the energy of impact but also vibrations. The elastic absorption phase, corresponding to the curve portion OM, is such that vibratory forces can be easily absorbed.

In an interesting application in this connection, devices embodying the invention may act as supports inserted between a vehicle chassis 8 and a container or other load borne by the chassis. During a first or elastic phase (curve OM) the supports absorb all the vibratory phenomena. In the second phase and the beginning of the third phase, if any, the supports can absorb impacts due to abrupt stops or any other causes.

The shock-absorbers may also be used as mountings for engines or other devices, e.g.

for boat engines, or as suspension devices for vehicles.

Compared with existing devices of the same kind, devices embodying the invention have numerous advantages, inter alia: The possibility of absorbing maximum energy for a given bulk.

Suitability for many different applications; The possibility of absorbing not only impacts but also vibrations; and Relative ease of manufacture.

Various modifications can be made in the above described embodiments of the invention within the scope of the claims. For example, the two bumpers shown in Figure 1 may be replaced by a single bumper extending all the way across the vehicle.

WHAT WE CLAIM IS: 1. A shock-absorbing device made of elastomeric material and of unitary construction, the device comprising two boundary walls interconnected by a network of walls to define a cellular structure having cells in the form of hollow prisms with their axes parallel to the boundary walls and with a polygonal cross-section, the cellular structure including: a first group of cells arranged in series transversely of the boundary walls and composed of at least two cells each having the same polygonal cross-section; and a second group of cells arranged in series transversely of the boundary walls and disposed adjacent to the first group of cells, the second group of cells being composed of at least one major cell having a cross-section of given polygonal shape and of two minor cells having a crosssectional shape corresponding to part of the given polygonal shape.

2. A shock-absorbing device according to claim 1, wherein the cells of the first group have the same cross-sectional shape as the or

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The inclined portion MN (Figure 6) corresponds to a special case only; the cells can be dimensioned so that portion MN is substantially parallel to the OX axis, as shown in Figure 7 at MN or MINI. Figure 8 is a diagrammatic illustration of various means of improving the curve and increasing the plateau and thus increasing the buckling possibilities. As can be seen from Figure 8, the following, inter alia, can be varied: The thickness of some walls, as shown at 13 where one wall has been made thinner, The shape of the walls, as diagrammatically illustrated at 14 where a bead facilitating buckling has been provided, or at 15 where the wall is curved or, The wall inclination, as shown at 16 in Figure 8. Of course, Figure 8 is diagrammatic only and is adapted to illustrate various features which can be used separately. Figure 9 shows a more concrete embodiment comprising beads 14. The set of bumpers is protected at the front by a protective metal frame 51, the rear holder on the vehicle having the reference 71. Figure 9 also illustrates the provision of holes 17 at the cell nodes, so as to increase their deformability. These various additional means of facilitating buckling can be used to obtain deformation due to buckling over a considerable proportion of the depth of the elastomeric unit. For example the deformation Ox (Figure 7) will be approximately 0.4p in the case of a unit as described in Figure 2, but can be increased to 0.6 p or more by using means such as shown inter alia on Figure 9. OMNP represents the curve obtained for a unit of the kind in Figure 2, whereas the curve becomes OM1N1P when the unit is formed as in Figure 9 or in similar manner. The hexagonal shape is no way indispensable, as shown by the variant in Figure 10, in which the cross-section of the cells 1 of the first group is pentagonal, some pentagon apices being disposed on bases 5 and 7. The cells are open at their ends, so that air is not compressed during deformation. However, there is no reason against providing elastomeric or other covers for at least partly closing the cells at the aforementioned ends. There is no reason, incidentally, against partly compressing the air in the cells. Instead of extending at right angles to the length of the device, i.e. vertically when applied to bumpers, the cells can extend in the longitudinal direction, i.e. horizontally in the present application, or may even extend obliquely. The application to bumpers, which has been described more specifically hereinbefore, is the most promising since all the impact energy can be absorbed in a relatively small volume, in the case of impacts at low speed and a given maximum absorbed force, without causing any damage to the vehicle However, this application is by no means the only possible application. More particularly, shock-absorbing devices according to the invention are of value in all cases in which it is necessary to absorb not only the energy of impact but also vibrations. The elastic absorption phase, corresponding to the curve portion OM, is such that vibratory forces can be easily absorbed. In an interesting application in this connection, devices embodying the invention may act as supports inserted between a vehicle chassis 8 and a container or other load borne by the chassis. During a first or elastic phase (curve OM) the supports absorb all the vibratory phenomena. In the second phase and the beginning of the third phase, if any, the supports can absorb impacts due to abrupt stops or any other causes. The shock-absorbers may also be used as mountings for engines or other devices, e.g. for boat engines, or as suspension devices for vehicles. Compared with existing devices of the same kind, devices embodying the invention have numerous advantages, inter alia: The possibility of absorbing maximum energy for a given bulk. Suitability for many different applications; The possibility of absorbing not only impacts but also vibrations; and Relative ease of manufacture. Various modifications can be made in the above described embodiments of the invention within the scope of the claims. For example, the two bumpers shown in Figure 1 may be replaced by a single bumper extending all the way across the vehicle. WHAT WE CLAIM IS:

1. A shock-absorbing device made of elastomeric material and of unitary construction, the device comprising two boundary walls interconnected by a network of walls to define a cellular structure having cells in the form of hollow prisms with their axes parallel to the boundary walls and with a polygonal cross-section, the cellular structure including: a first group of cells arranged in series transversely of the boundary walls and composed of at least two cells each having the same polygonal cross-section; and a second group of cells arranged in series transversely of the boundary walls and disposed adjacent to the first group of cells, the second group of cells being composed of at least one major cell having a cross-section of given polygonal shape and of two minor cells having a crosssectional shape corresponding to part of the given polygonal shape.

each major cell of the second group.

3. A shock-absorbing device according to claim 1 or 2, wherein the or each major cell of the second group has a hexagonal crosssectional shape.

4. A device according to any one of claims 1 to 3, wherein the boundary walls are elongate and the axes of the cells extend transversely of the length of the boundary walls.

5. A device according to any preceding claim, wherein means for facilitating deformation of the cellular structure by resilient buckling of the cell walls is provided on some walls of the cells.

6. A device according to claim 5 wherein the means for facilitating buckling comprise beads on some of the walls.

7. A device according to any preceding claim wherein the walls of at least some of the cells adjacent each boundary wall are of reduced thickness compared to the walls of the other cells.

8. A device according to claim 7 wherein the reduced thickness cell walls are from 50%to 75 % of the thickness of the other cell walls.

9. A device according to claim 6 or 7, wherein the walls of the minor cells of the second group are the reduced thickness walls.

10. A device according to any preceding claim, wherein the thickness of the cell walls is of the order of a quarter of the length of the sides of the cell cross-section.

11. A device according to any preceding claim, wherein the cells are open at their axial ends.

12. A shock-absorbing device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.