AU731441B2 - Impact absorbing device - Google Patents

Description

-i 1- P/00/0 IIi Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT a a i

ORIGINAL

Name of Applicant: Actual Inventors: Address for service ARB CORPORATION LIMITED To Be Advised in Australia: CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia Invention Title: IMPACT ABSORBING DEVICE Details of Associ ated Provisional Application: P05144 filed 17 February 1997 The following statement is a full description of this invention, including the best method of performing it known to us -2- TITLE IMPACT ABSORBING DEVICE This invention relates to an impact absorbing device and in particular to an impact absorbing collapsible support mounting in which the load deformation response of the support mounting can be changed to a desired predetermined level.

The invention also relates to a method of providing a predetermined load deformation response to a collapsible support member.

In the design of modem motor vehicles, the use and fitting of air bags as a driver and passenger restraint has become common practice. The air bag generally has an associated inertia detector which is tuned to trigger and inflate the air bag at a particular moment during a frontal collision into a concrete barrier. The correct firing of the air bag depends on the crash pulse during the collision which in turn depends on the load deformation response or energy absorption characteristics of the o vehicle components at the front end of the vehicle. When replacing or modifying components in the front end of the vehicle, it is essential for the correct firing of the 15 air bag that the load deformation response of the replacement or modified °o components resembles that of the components which have been replaced. If the load deformation response of the replaced components varies greatly from the original components, then the air bag will either trigger prematurely or unnecessarily, or it will fire during a collision, well after the time when the inflation of the air bag would be of any real benefit.

Therefore, it is imperative when replacing components in the front end of a °ooto° vehicle such as the bumper bar with modified components such as bull bars or crash bars that the load deformation behaviour of the front end of a vehicle is not significantly changed so as to affect the timing of the firing of the air bag. When replacing or modifying front end components it is not always clear at what point in time during a collision the air bag fires, and so it is important that the load deformation characteristics of components are closely replicated by the replacement components.

In addition, all vehicles released on to the market have already been certified in a full scale concrete barrier crash test and by replicating the load deformation BCI:JIH:#19134.CAP 17 Febmary 1998 behaviour of any components which are replaced, it will not be necessary to carry out further large scale crash test with the new replacement or modified components fitted.

Thus, it is an objective of the present invention to provide a method of replicating the load deformation response of components and an impact absorbing device which enables replication of the load deformation response of a component to be replaced.

Accordingly in one aspect, the invention provides an impact absorbing device having a support member with a predetermined load deformation response including an elongate hollow member having two end sections and a plurality of longitudinally extending grooves between the end sections which define a plurality of load bearing side walls, each side wall having at least one laterally extending line of weakness such that a compressive load applied to either of the end sections results in a longitudinal separation of the side walls along the longitudinally extending grooves and folding along the at least one lateral line of weakness as the device compacts, said load deformation response being predetermined by determining the effect with depth and number of lateral lines of 15 weakness across the side walls have on the load deformation response of the support member, and based on this determination, forming said lines of weakness to provide the predetermined load deformation response in said support member.

It is preferable that the longitudinally extending grooves are slits through the elongate hollow member and the side walls are defined by at least one slit extending 20 between the end sections.

0oo•0 The purpose of the at least one lateral line of weakness is to provide a line for folding of the side walls and the outer surfaces of the elongate member. The applicant :has found that the load deformation characteristics of the elongate member can be predictably modified by adjusting the resistance to folding along the lateral line of weakness which are preferably grooves or troughs formed in the side walls preferably giving the side walls an undulating cross-section.

In a preferred form of the invention, the depth of the lateral trough in the side walls of the elongate member may vary along the length of each trough and when more than one trough is formed, there may be variations in the depth of each trough along the length of the elongate member. The lateral troughs may be formed in the inner surface of the side walls producing corresponding ridges in the outer surface of the side walls.

22 January 2001 It may be desirable in some instances for the depth of a trough in some places to be such that a notch or lateral slit extends through the side wall and the corresponding ridge formed in the outer surface of the side wall is separated into at least two discrete sections.

It can be seen that the provision of the troughs and corresponding ridges in the side wall of the elongate member effectively provides hinges for folding of the side wall.

The troughs may have rounded, square-shaped or triangular bottoms depending on the load formation response required.

Another aspect of the invention relates to a method of providing a predetermined load deformation response in a support member including a hollow elongate member having two end sections and a plurality of longitudinal grooves extending between the end sections to define a plurality of load bearing side walls, the load bearing side walls having at least one line of weakness, the method including the steps of: determining the effect which the depth and number of lateral lines of weakness 15 across the side walls have on the load deformation response of the supporting member, and 2) based on this determination forming at least one lateral line of weakness in the side walls to provide the desired load deformation response to the support member.

The at least one line of weakness may be a lateral trough formed in the side wall, a corresponding ridge being formed in the opposite side of the side wall.

Once the load deformation response of the support mountings to be replaced have been determined, the above method can be used to substantially replicate that load deformation response.

A third aspect of the invention relates to a method of providing a predetermined load deformation response to a support member including a hollow elongate member having two end sections and a plurality of longitudinal grooves extending between the end sections to define a plurality of load bearing side walls, the load bearing side walls having a least one lateral line of weakness, the method including the steps of: 22 January 2001 determining the load deformation response of a sample support member, varying the number and depth of the lateral lines of weakness in each side wall of thesample support member, repeating step on a plurality of sample support members, determining the effect which the depth of the line of weakness and the number of lines of weakness have on the load deformation response of said sample support members from the results of steps and above, and forming at least one lateral line of weakness in the side walls of the support member to provide a predetermined load deformation response to said support member.

longitudinal grooves formed in the elongate hollow member defining the side walls are preferably slits through the elongate member extending between the end sections. The lateral troughs are preferably formed in the inner surface of the side walls producing corresponding ridges in the outer surface of the side walls.

These ridges and troughs act effectively as hinges for folding of the side walls when a load is applied to either or both end sections of the elongate member.

The load deformation response of the side walls can be varied by changing the depth of the lateral troughs with a corresponding change in the height of the ridges and by changing the number of troughs and ridges in each side wall. A notch may be formed in the ridge extending through the side wall thereby forming a discontinuity in the corresponding ridge.

The applicant has found that the application of the above method enables a support mounting to be designed to have a desired load deformation profile which substantially replicates a load deformation profile of the support mounting to be replaced.

Further features, objects and advantages of the present invention will now become more apparent from the following description of the preferred embodiment and accompanying drawings, in which:- Figure l(a) is a top perspective view of an impact absorbing structural mount in accordance with the present invention; BCJIH:#19134.CAP1 17 Febury 1998 -6- Figure l(b) is a bottom perspective view of the embodiment shown in Figure la; Figure 2 is a sectional view of the impact absorbing device of Figure 1 through section 2-2; Figure 3(a) is a schematic diagram of a kinked strut; Figure 3(b) is an illustrative curve of load displacement; Figure 4 is a schematic diagram comparing a kinked strut to a ridged strut; Figures are predicted load-deformation response curves and corresponding side wall profiles for the samples of Table 1; Figures 18 are schematic representations showing the mechanism of "collapse of the profile shown in Figure 4; Figures 19-31 are side wall profiles and corresponding predicted loade deformation curves for samples shown in Table 2; Figure 32 is a load deformation comparison between the existing ARB Bull Bar Mounting, the Land Rover Discovery crash can and the predicted sample of Figure 31.

Figure 33 is a load deformation response of a Land Rover Discovery bumper bar crash can; and Figures are schematic representations showing the mechanism of collapse of the profile shown in Figure 31.

Referring to the drawings, Figures 1 and 2 show an impact absorbing device 1 in accordance with the preferred embodiment of the invention is shown.

The device 1 comprises an elongate hollow member 2 having two end sections 3, 4 and a plurality of longitudinal grooves 5 extending between the end sections 3, 4. The longitudinal grooves 5 define load bearing side walls 6, each side wall having at least one lateral line of weakness or trough 8 extending across the side wall. The longitudinal grooves each define a line of weakness between the side walls and are preferably slits formed in the elongate hollow member 2. When a compressive load is applied at either or both end sections 3, 4, the side walls 6 are each able to deform separately because of the existence of these longitudinal BC.IH:#19134.CAP 17 Fcbuary 1998 -7grooves.

The purpose of the at least one lateral groove or trough 8 formed in the side walls 6 is to provide a line of weakness for folding of the elongate member 2. As shown in Figure 2 the lateral troughs 8 are preferably formed in the inner surface of the side walls 6 producing corresponding ridges 10 in the outer surface of the side walls 6.

When a compressive load is applied to one or both end sections 3, 4 of the elongate member 2, the load bearing side walls 6 fold preferably outwardly.

As stated above due to the presence of the longitudinal slits or grooves 5, the side walls 6 separate along the longitudinal grooves or slits and fold independently along the lateral grooves. In order for the device according to the invention to collapse axially in response to an axial compressive load, it is desirably for each side S-wall to have identical load bearing capabilities and this is best attained by providing the same number of grooves or troughs in each side wall with each corresponding trough having the same depth.

To vary the load deformation of the side walls, one or more lateral grooves or troughs are formed in the side walls 6. The depth of the lateral troughs along S. each side wall may vary depending on the load deformation response required. An increase in the depth of the lateral trough results in a corresponding increase in the height of the ridge.

Another means of varying the load deformation characteristics of the side wall is to remove a section of the ridge by forming a notch 9. This means of varying load deformation may be used as an alternative to varying the depth of the troughs or used in conjunction with such variations in trough depth to provide the desired load deformation response.

The mounting support is also provided with mounting holes 11 for securing the mounting support to the vehicle support and the bumper bar, bull bar or crash bar.

In order to replicate the load deformation of a vehicle component such as a mounting support for a front bumper bar, the original mounting support was placed BC'JH:19134.CAP9 17 Fb u"m 1998 -8in a 50 ton Baldwin Universal testing machine and a compressive load applied in displacement control mode. A constant cross head velocity was applied to the support irrespective of load magnitude. From the test, a load deformation response of the original mounting support was obtained.

A number of load deformation tests were then conducted on the impact absorbing device according to the preferred embodiment of the present invention using a number of different side wall profiles.

From previous work on impact absorption, it was known that the load deformation behaviour of a kinked strut shown in Figure 3 subjected to an impact load can be predicted using simple beam theory and the initial peak load can be reduced by initiating the kink. Thus it is only necessary to introduce an offset A to reduce the peak load. While this theory provides a basis to reduce the peak load S-required to cause plastic deformation, in practice it is difficult to manufacture a support mounting or the like component with a specified offset to provide the necessary kink in the component.

.*The applicants have found that this offset can also be introduced into a component by providing a small trough and corresponding ridge in a side wall as shown in Figure 4 in which the height of the ridge is equivalent to the offset A in a kinked member and the strut arm length L is equivalent to the distance from one end of the plate to the peak of the ridge.

A number of tests were then conducted using the impact absorbing device of i the present invention. In the tests the number of troughs and the depth of trough were varied to determine the effect such variations had on the load deformation response of the impact absorbing device of the present invention.

Table 1 is a summary of the samples used in the finite element model evaluation.

BCJH:919134.CAP 17 Fcbruw 1998 9- Table 1: Summary of finite element models analysed S S

S.

.5.5.5 SFig FE MdlNo. of Offset ArPlt SMdlGrooves A(mmn) Length Thickness (mm) -tm) ARB1 1 10 60 4 6 ARB2 1 12 60 4 7 ARB3 3 15 30 4 8 ARB4 4 20 &30 25 4 9 ARB5 5 15 15 4 10 ARB5b 5 15 &30 15 4 11 ARB5c 5 15, 22.5 15 4 &&30 12 ARB5d 5 15, 19, 15 4 26.5 30_ 13 *AJ(B5dten 5 15, 19, 15 4 26.5 14 ARB6 5 20 15 "*Horizontal slot 40%,30% 25%,25% 15 ARB6b 5 20 15 "*Horizontal slot 40%,15%, 25%,25% 16 ARB5d 5 15,19,26.5 15 4 17 ARB6b 5 20 15 "*Horizontal slot 40%,15%, 0%1, 25%,25% is the same as ARB35d but subjected to tension load, percentage reduction in width of the fold Eight noded plane strain area elements were used to model the plate profiles.

Contact between the folds was modelled but contact friction was not included. Both BCJH:ff19134.CAP 7Fbuay19 17 Fcbruary 1998 .1 ends of the model were fixed against rotation, ie. six nodes in total were restrained, three at either end. A displacement control iterative procedure was used to simulate movement at one end of the model. The reactions at the other end of three nodes were monitored.

Figure 5 shows a model where the trough is shallow compared to Figure 6 which shows a deeper trough.

In the load deformation response of both profiles there are two peaks.

However for the longer shallower trough of Figure 5, the first peak is higher and the residual collapse load is extended. For the second shorter deeper trough in Figure 6, the first peak is lower than the second peak and the residual collapse load is shorter. It is clear that while the overall peak loads in both cases are similar, the point at which the ends of the trough make contact during the test is different. By manipulating the length and shallowness of the trough, it is possible to smooth out load deformation curve into a constant load deformation curve.

Figure 7 shows a impact absorbing device having three troughs in the side wall. The peak load is reduced from 115 newtons to 65 newtons and the load does S"not drop below 30 newtons.

Figure 8 shows a side wall profile having four troughs of varying depths or offset A and a profile which would bring into contact very quickly during a load test, the side walls of the trough. The load deformation curve displays a more constant behaviour with values oscillating between 50 and 100 newtons.

Figures 8 12 show variations of different multiple troughs having different trough depths or offsets A. Whilst the model of Figure 12 provides a suitably constant load deformation profile, it is difficult to manufacture troughs of varying depths. For this reason, the profiles shown in Figures 14 and 15 were analysed.

In this case a 20mm trough depth was maintained whereas the cross sectional areas at the ridge peaks were reduced and the percentage amounts indicated in Table 1 relative to the trough centre.

Figures 16(a) 16(b) show the results of Figures 13 and 15 in a more conventional format where each of the troughs are clearly labelled and the nodal BCJH:M19134.CAP 17 Fcbruary 1998 11loads have been added together and multiplied by 320mm.

It is clear from Figures 16(a) and 16(b) and 17(a) and 17(b) that the variable depth model provides a smoother constant load. Figure 17(b) also shows what effect varying the yield strength has on the load deformation behaviour, ie. it simply moves the curve higher.

Figure 18(a)-18(h) shows a profile of a side wall showing the mechanism by which the ends of the troughs contact and collapse the troughs.

In order to replace the bumper bar of a vehicle with a modified bumper bar such as a bull bar, the crash cans of a Range Rover Discovery were tested to provide the load deformation curve shown in Figure 33. The plots show that there are little variation between the two cans. Whilst the peak load was approximately 8 tons, it occurred at a displacement of 110mm. Once the cans were completely crushed the load began to rise as a result of the solid cantilever attachment bar resisting deformation. The relatively low load up to a deformation of approximately is the compression of the Discovery's plastic bumper bar cover. This portion of the load deformation curve was ignored during the design of the mounting system in accordance with the present invention. It was felt that a new plastic cover can be readily manufactured and placed on the bull bar to simulate this portion of the curve.

BCJH:W19134.CAP 17 Fcujy 1998 12- Table 2: Summary of models analysed in order to develop the triangulated Discovery crush can curve 0@@ Fig Model Offset Arm Length Central Length Contact (mm) (mm) (mm) friction 19 ARBNEW1 25 56 50 no 20 ARBNEW2 25 65 30 no 21 ARBNEW3 25 65 30 yes 22 ARBNEW4 20 18 50 yes 23 ARBNEW5 10 15 18 50 yes 24 ARBNEW6 20 18 40 yes 10 25 ARBNEW7 20 18 30 yes 26 ARBNEW8 25 18 30 yes 27 ARBNEW9 20 25 12 30 yes 28 ARBNEW10 20 25 12 20 yes 29 ARBNEW11 20 12 4 x 11 yes 30 ARBNEW12 15 20 15 4 x 11 yes 31 ARBNEW13 2+15 20 15 4 x 11 yes Based on the results of the previous load deformation tests, a number of alternate profiles shown in Table 2 were trialed in an attempt to replicate the load deformation curve of the Range Rover Discovery bumper bar. Of the variations shown in Table 2, the closest predicted load deformation curve is shown in Figure BC-JH:W19134.CAP 17 Fbunry 1998 13 31. The predicted load deformation curve for sample ARBNEW13 has been superimposed onto the load deformation curve for the Discovery crash can test and is shown in Figure 32. It can be seen from the super imposition of the two load deformation curves that the load deformation curve for ARBNEW13 has a similar general shape to the Discovery crash can response but the peaks occur at deflections which are less than those of the Discovery crash can test. The difference in the deformation required before the peaks occur can be taken into account and adjusted by adjusting the depths of the troughs and the length of any slits.

It should be emphasised that while the predicted curve is jagged, it is not too dissimilar in shape to the curve developed in Figure 33. Once this profile of side wall for the impact absorbing device of the present invention is tested, it is expected that much of the jaggedness of the curve is expected to be smoothed out.

o* S° Figure 34 shows the collapse mechanism of the side wall profile shown in Figure 31. It can be seen by developing an understanding of the effect which the 15 depth of the troughs and the number of troughs has on load deformation response of the side walls, an impact absorbing device having desired load deformation characteristics can be designed. The parameters used to design the impact absorbing device with the desired load deformation characteristics include the number of troughs, the depth of troughs, the distance between the end of each trough, and the length of any plateau which is formed in the side wall between the troughs.

Thus by developing an understanding of the effect the above parameters-have on the load deformation response of the impact absorbing device according to the present invention, a predetermined load deformation response can substantially be designed into the device.

BCJH:A19134.CAP 17 Fcbuary 1993

Claims (21)

1. An impact absorbing device having a support member with a predetermined load deformation response including an elongate hollow member having two end sections and a plurality of longitudinally extending grooves between the end sections which define a plurality of load bearing side walls, each side wall having at least one laterally extending line of weakness such that a compressive load applied to either of the end sections results in a longitudinal separation of the side walls along the longitudinally extending grooves and folding along the at least one lateral line of weakness as the device compacts, said load deformation response being predetermined by determining the effect with depth and number of lateral lines of weakness across the side walls have on the load deformation response of the support member, and based on this determination, forming said lines of weakness to provide the predetermined load deformation response in said support member.

2. The impact absorbing device according to claim 1, wherein the longitudinal grooves are slits through the elongate hollow member and the side walls are defined by at least one slit extending between the end sections.

3. The impact absorbing device in accordance with either one of claims 1 or 2 .:000: wherein the at least one lateral line of weakness in the side wall provides a line for folding of the side walls. 20

4. The impact absorbing device according to claim 3 wherein the at least one lateral line of weakness is a groove or trough formed in the side wall.

5. The impact absorbing device according to claim 4 wherein the groove or trough formed in the side wall give the side wall an undulating cross-section.

6. The impact absorbing device according to claims 4 or 5 wherein the depth of the lateral trough in the side walls of the elongate member is varied along the length of each trough.

7. The impact absorbing device according to any one of claims 4 to 6 wherein a plurality of troughs are formed in each side wall.

8. The impact absorbing device according to claim 7 wherein the depth of each trough varies along the length of the elongate member. 22 January 2001

9. The impact absorbing device according to any one of claims 4 to 8 wherein the lateral trough is formed on the inner surface of the side wall producing corresponding ridges in the outer surface of the side wall.

The impact absorbing device according to claim 9 wherein the trough or troughs are provided with a notch or lateral slit extending through the side wall causing the corresponding ridge formed in the outer surface of the side wall to be separated into at least two discrete sections by the notch or lateral slit.

11. The impact absorbing device according to any one of claims 4 to 10 wherein the bottom of the trough is rounded, square-shaped or triangular.

12. A method of providing a predetermined load deformation response in a support member including, a hollow elongate member having two end sections and a plurality of longitudinal grooves extending between the end sections to define a plurality of load bearing side walls, the load bearing side walls having at least one lateral line of weakness, the method including the steps of, determining the effect which the depth and number of lateral lines of 15 weakness across the side wall have on the load deformation response of the supporting member, and based on this determination forming at least one lateral line of weakness in the g side walls to provide the predetermined load deformation response in the support member.

13. The method according to claim 12, wherein the at least one lateral line of weakness includes at least one lateral trough formed in the side walls of the elongate element, the trough oo having a corresponding ridge formed in the opposite side of the side wall.

14. A method of providing a predetermined load deformation response to a support oo member including a hollow elongate member having two end sections and a plurality of "longitudinal grooves extending between the end sections to define a plurality of load bearing "side walls, the load bearing side walls having a least one lateral line of weakness, the method including the steps of: determining the load deformation response of a sample support member, varying the number and depth of the lateral lines of weakness in each side wall of the sample support member, repeating step on a plurality of sample support members, determining the JB:JH:40228598RS 22 January 2001 16 effect which the depth of the line of weakness and the number of lines of weakness have on the load deformation response of said sample support members from the results of steps and above, and forming at least one lateral line of weakness in the side walls of the support member to provide a predetermined load deformation response to said support member.

The method or providing a predetermined load deformation response to a support member according to claim 14 wherein the at least one lateral line of weakness in the side walls is provided by forming a trough and corresponding ridge in the side walls of the elongate member.

16. The method of providing a pre-determined load deformation response to a support member according to claim 14 or 15 wherein the longitudinal grooves formed in the elongate hollow member defining the side walls are slits through the elongate member extending between the end sections.

17. A method of providing a pre-determined load deformation response to a *SS* o* 9* support member according to claim 15 or 16 wherein the lateral troughs are formed in the inner surface of the side walls producing corresponding ridges in the outer surface of the side walls, the ridges and troughs acting as hinges for the folding of the side walls when a load is applied to either or both ends of the elongate member. 20

18. The method of providing a pre-determined load deformation response to a support member according to any one of claims 15 to 18 wherein the load deformation response of the side wall is varied by changing the depth of the lateral troughs with a corresponding change in the height of the ridges or by changing the number of troughs and ridges in each side wall.

19. The method of providing a pre-determined load deformation response to a support member according to claim 18 wherein at least one ridge in the side wall is provided with a notch or slit extending through the side wall forming a discontinuity in the ridge.

BCIH:#19134.CAP 17 F~nbuary 1993 17- An impact absorbing device substantially as hereinbefore described with reference to the accompanying drawings.

21. A method of providing a pre-determined load deformation response to a support member substantially as hereinbefore described with reference to the preferred embodiment. DATED: 17 February 1998 CARTER SMITH BEADLE Patent Attorneys for the Applicant: ARB CORPORATION LIMITED 0* 6500 BCJH:19134.CAP 17 Febmary 1998