GB2422136A

GB2422136A - A bumper assembly for an automobile having a composite crush can

Info

Publication number: GB2422136A
Application number: GB0500583A
Authority: GB
Inventors: David John Marler
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2005-01-12
Filing date: 2005-01-12
Publication date: 2006-07-19
Anticipated expiration: 2025-01-12
Also published as: GB0500583D0; GB2422136B

Abstract

The present invention provides a bumper assembly for an automobile comprising a bumper (20) secured to a supporting structure (22) therebehind by a mounting bracket (24) with a crush can (30) extending within the bracket between the supporting structure (22) and the bumper (20) . The mounting bracket (24) is formed of a first composite material comprising fibres set in a first thermoplastic matrix. The crush can (30) is formed of a second composite material comprising fibres set in a second different matrix. In response to an impact, the crush can (30) disintegrates progressively with the fibres separating from the resin of the matrix in which they are fixed and the mounting bracket (24) buckles as the crush can (30) disintegrates. The mounting bracket (24) maintains a connection between the bumper (20) and the supporting structure (22) throughout the disintegration of the crush can (30). The fibres in both the crush can and the mounting bracket may be glass fibres, those in the mounting bracket extending lengthwise of the bracket. The crush can (see figure 5) may be formed from a plurality of Z-shaped components.

Description

A BUNPER ASSEMBLY FOR AN AUTOMOBILE

The present invention relates to a bumper assembly for an automobile.

Conventionally, bumpers are secured to a supporting structure lying behind them by way of a pivot joint. A bolt or pin extending vertically defines a pivot axis about which the bumper can pivot when it deflects in response to a force applied to it. This S illustrated by figure 1, which is a schematic plan drawing of the bumper arrangement of a conventional vehicle, in which a bumper 10 is secured to two crash rails 11 and 12 by mounts which include vertically extending pivot points (e.g. bolts or pins) 13 and 14. The mounting brackets 15 and 16 for the pivots 13 and 14 are metallic and have rear portions which act as crush cans and in which folds are formed during an impact, the crush can thus absorbing energy.

More recently composite crush cans have been used in place of metallic crush cans. A composite crush can comprises fibres (glass or carbon) set in a resin matrix.

It is designed to disintegrate from the front backwards absorbing collision energy in the process. The use of composite crush cans in place of the traditional metallic crush cans presents a technical problem in retaining some sort of physical connection between the bumper and the support structure therebehind during disintegration of the crush cans. Since the failure mechanism of the metallic crush cans is a folding, buckling failure, there remains during deformation a structure in the crush cans capable of retaining the bumper on the supporting structure, i. e. preventing it becoming detached from the vehicle. However, with a composite crush can, once it starts to fail there is no longer a connection between the bumper and the supporting structure which resists the weight of bumper and the bumper would fall off the vehicle due to gravity during or after an impact if composite crush cans are used to simply replace the metallic crush cans of Figure 1.

The present invention in a first aspect provides a bumper assembly for an automobile comprising a bumper secured to a supporting structure therebehind by a mounting bracket with a crush can extending within the bracket between the supporting structure and the bumper, wherein: the mounting bracket is formed of a first composite material comprising fibres set in a first thermoplastic matrix; the crash can is formed of a second composite material comprising fibres set in a second different matrix; and in response to an impact the crush can disintegrates progressively with the fibres separating from the resin of the matrix in which they are fixed; and the mounting bracket buckles as the crush can disintegrates and the mounting bracket maintains a connection between the bumper and the supporting structure throughout the disintegration of the crush can.

In a second aspect, the present invention provides a bumper assembly for an automobile comprising a bumper secured to a supporting structure therebehind by a plurality of mounting brackets with a crush can extending within each bracket between the supporting structure and the bumper, wherein each mounting bracket is formed of a first composite material comprising fibres set in a first thermoplastic matrix; each crush can is formed of a second composite material comprising fibres set in a second different matrix; and in response to an impact each crush can disintegrates progressively with the fibres separating from the resin of the matrix in which they are fixed; and each mounting bracket buckles as the crush can located therewithin disintegrates and each mounting bracket maintains a connection between the bumper and the supporting structure throughout the disintegration of the crush can.

The present invention enables the use of a bumper assembly formed from thermoplastics and/or thermosets whilst ensuring the bumper is Supported by the support structure of the vehicle during impact. Also the brackets of the bumper arrangement allow Pivoting of the bumper without the need for pivot pins.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic plan view of a conventional

bumper assembly of the prior art;

Figure 2 is a schematic perspective view of a bumper assembly according to a preferred embodiment of the present invention; Figure 3 is a side elevation view of the bumper assembly of Figure 2; Figure 4 is a schematic rear perspective view of a front crash structure of a vehicle comprising the bumper assembly of Figures 2 and 3; and Figure 5 is an illustration of Z-shaped component of a crush tube of the bumper assembly of Figures 2 to 4.

Turning now to Figure 2, there can be seen in the figure a bumper 20 connected to a main crash rail 22 of a front crash structure of an automobile by a bumper mounting bracket 21 made of a composite material comprising glass fibres set in a thermoplastic matrix. The bracket 21 is formed as an open U-shaped section, as can be seen in the side elevation of Figure 3, having two arms 23, 24 extending forwardly from a base 25. Each arm e.g. 23 has a first section, e.g. 23A, proximal a crash rail, e. g. 22, which flares upwardly (or downwardly in the case of the lower arms) at a first gradient and a second section, e.g. 23B, which flares upwardly (or downwardly in the case of the lower arms) at a second lesser gradient; a line, e.g. 23C, marks the change in gradient. The base 25 is mounted on a back plate 80 which is bolted to the crash rail 27 by bolts 81, 82. The back plate 80 will be of the same thermoplastic composite material as the bracket to enable the bracket to be heat welded to the backplate 80. The bolts e.g. 81, 82 enable easy removal of the brackets after a collision. The front parts of the arms 23, 24 are provided with flanges 26, 27 (see Figure 4) which enable the arms 23, 24 to be secured to a rear surface of the bumper 20. The bumper 20 will be of a thermoplastic and the flanges 26, 27 will be welded to the bumper 20. When viewed from above each of the arms 23, 24 is generally quadrilater in form with the bracket side of each arm shorter than the bumper side and with the sides nearer the bumper centre longer than the sides facing the transverse edges of the bumper 24.

In Figure 4, it can be seen that the bumper 20 is part of a front bumper assembly comprising two identical brackets 21, 41 securing the bumper 20 to two crash rails 22, 42.

Inside each bracket 21, 41 there is provided a crash can (30, 50 in the figures) which is of a composite material such as glass fibres set in a thermoset or thermoplastic resin matrix. Each crush can 30, 50 is a hollow body of a generally rectangular cross-section Each crush can is formed from two components as illustrated in Figure 5, in which two Z-shaped components ioo, 102 are welded together along faces 103/104 and 105/106 to form a crash rail with a rectangular cavity 107 running therethrough. The same Z - shaped sections ioi, 102 can be used to form several crush cans with cavities of differing dimensions (by varying the width of the contact patches between surfaces 103/104 and 105/106) Bolts or welding can be used to secure a front end of each crush can 30, 50 directly to the bumper 20. A rear end of each crush can 30, 50 is mounted on a forwardly facing surface of the base (e.g. 25) of each bracket. The front ends of the crush cans 30, 50 extend into a recess 70 provided in the rearwardly facing surface of the bumper 20 and thus the crush cans 30, 50 engage the bumper at locations forward of the front flanges (e.g. 26, 27) by which the brackets 21, 41 are attached to the bumper 20. In this way the length of each crush can 30, 50 is maximised.

During an impact each bracket 21, 41 buckles (as shown in dotted lines in Figure 3) about the lines, e.g. 23C, defining the change in gradient between the base and bumper sections of the arms. In buckling each bracket forms a plastic hinge defining a generally vertically extending axis about which the bumper 20 can rotate. Thus pivot type behaviour is provided in the mounts of the bumper without the need for a traditional pivot joint. Looking at Figure 3, plastic hinges will define axes 110,111 about which the bumper 20 can pivot; this is achieved by configuring the brackets with the form illustrated in the drawings and in particular with the inner sides longer than the outer sides - the longer faces collapse first.

During an impact each crush can 30, 50 is crushed with the crushing of the crush cans 30, 50 absorbing energy of the impact. Each crush can 30, 50 is retained within the respective bracket 21, 41 during crushing of the crush can 30, 50 and with the brackets 21, 41 maintaining connection between the bumper 20 and the main crash rails 22, 42 throughout collapse of the crush cans 30, 50.

After a collision the crush cans and bumpers can be removed as a single unit by unbolting the brackets 21, 41 from the crash rails 22 and 42. A new bumper arrangement can then be bolted in place as a single unit.

Each crush can can be bolted or bonded to the bumper and the base of a bracket. Whilst glass-fibre reinforced composite crush cans are described above, more expensive carbon-fibre composite crush cans could be used (and, less preferably, metallic crush cans could be used) The brackets are formed with a thermoplastic matrix because of the flexibility of thermoplastics (thermosets are less flexible and more brittle) . Also the cycle time to manufacture a thermoplastic component is much less than the cycle time to manufacture a thermoset component (e.g. 2 minutes rather than 50 minutes) . The thermoplastics used could be nylon, PBT or sPS. The fibres in the brackets may be paid up lengthwise to facilitate the desire buckling mode during an impact.

The bumper 20 will typically be moulded in a thermoplastic with the same matrix material of the brackets so that the brackets can be easily welded to the bumper.

The crush cans will be formed with a thermoplastic or thermoset resin matrix, but if a thermoplastic is used then it will not necessarily be the same as the thermoplastic of the brackets and bumper.

Claims

1. A bumper assembly for an automobile comprising a bumper secured to a supporting structure therebehind by a mounting bracket with a crush can extending within the bracket between the supporting structure and the bumper wherein: the mounting bracket is formed of a first composite material comprising fibres set in a first thermoplastic matrix; the crash can is formed of a second composite material comprising fibres set in a second different matrix; and in response to an impact: the crush can disintegrates progressively with the fibres separating from the resin of the matrix in which they are fixed; and the mounting bracket buckles as the crush can disintegrates and the mounting bracket maintains a connection between the bumper and the supporting structure throughout the disintegration of the crush can.

2. A bumper assembly for an automobile comprising a bumper secured to a supporting structure therebehind by a plurality of mounting brackets with a crush can extending within each bracket between the supporting structure and the bumper, wherein: each mounting bracket is formed of a first composite material comprising fibres set in a first thermoplastic matrix; each crush can is formed of a second composite material comprising fibres set in a second different matrix; and in response to an impact: each crush can disintegrates Progressively with the fibres separating from the resin of the matrix in which they are fixed; and each mounting bracket buckles as the crush can located therewithin disintegr5 and each mounting bracket maintains a connection between the bumper and the supporting structure throughout the disintegj0 of the crush can.

3. A bumper assembly as claimed in claim 1 or claim 2 wherein the/each mounting bracket is formed of fibres set in a thermoplastic matrix.

4. A bumper assely as claimed in claim 3 wherein the fibres are glass fibres.

5. A bumper assembly as claimed in any one of the Preceding claims wherein the fibres in the or each bracket extend lengthwi5 of the bracket.

6. A bumper assembly as claimed in any One of the Preceding claims wherein the or each bracket is U-shaped and has a base secured to the supporting structure from which extend two arms secured at their distal ends to a back surface of the bumper.

7. A bumper assembly as claimed in claim 6 wherein each arm is sheet-like and in form, having a bumper side longer than a base side.

8. A bumper asse1y as claimed in claim 7 wherein the other two sides of the quadrilate are unequal in length.

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9. A bumper assembly as claimed in claim 6 or claim 8 wherein each arm has a flanged portion via which the arm is secured to the bumper.

10. A bumper assembly as claimed in any one of claims 6 to 9 wherein the or each mounting bracket is U-shaped when viewed in a side elevation.

11. A bumper assembly as claimed in any one of claims 6 to 10 wherein the arms of the/each lead bracket are spaced one above the other and flare apart as they extend toward the bumper, one flaring upwardly and the other downwardly, and each arm has a base section nearer the base of the bracket and a bumper section nearer the bumper, the base section flaring with a first gradient and the bumper section flaring with a second gradient different to the first section, a line extending transversely across each arm where the base section meets the bumper section of the arm and said line defining a location for a plastic hinge which forms in the arm when the/each bracket buckles.

12. A bumper assembly as claimed in any one of the preceding claims wherein in the/each bracket a generally vertically extending pivot axis is defined by a plastic hinge formed during buckling of the/each bracket, the vertically extending pivot axis allowing a bumper section to rotate thereabout.

13. A bumper assembly as claimed in any one of the preceding claims wherein the/each bracket is formed as an open section, being open at both transversely spaced sides thereof.

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14. A bumper assembly as claimed in any one of the preceding claims wherein the/each bracket is welded to the bumper and is secured to the supporting structure by mechanical fasteners which can be unfastened to allow the bumper assembly to be detached from the supporting structure as a single unit.

15. A bumper assembly as claimed in any one of the preceding claims wherein the/each crush tube is formed from a plurality of Z-shaped components fixed together to form a rectangular cross-section hollow crush tube.

16. A bumper assembly as claimed in claim 15 wherein each Z-shaped component has a middle section which extends in use substantially vertically and two edge sections, one extending Perpendicularly in a first direction from the middle section at the top of the middle section and the other extending Perpendicularly in a second direction opposite to the first direction from the middle section at the bottom of the middle section, wherein an upper surface of each edge section of one Z-shaped component is brought into abutment with a lower surface of a corresponding edge section of another Z-shaped component in the formation of the crush tube.

17. A bumper assembly as claimed in any one of the preceding claims wherein the bumper is provided with a recess in a back surface thereof and the/each crush can extends into the recess to engage the bumper at a point further distanced from the base of the bracket than the - 12 - points at which the distal ends of the arms engage the back surface of the bumper.

18. A bumper arrangement substantially as hereinbefore S described with reference to and as shown in the accompanying figures 2 to 5.