GB2536888A

GB2536888A - An energy absorption assembly

Info

Publication number: GB2536888A
Application number: GB1505331.7A
Authority: GB
Inventors: David Williams Terence; Moreno Carlos
Original assignee: T A Savery and Co Ltd
Current assignee: T A Savery and Co Ltd
Priority date: 2015-03-27
Filing date: 2015-03-27
Publication date: 2016-10-05
Also published as: WO2016156793A1; GB201505331D0

Abstract

An energy absorption assembly 10 having a hollow deforming tube 11; and a dual-function die 14 including an expansion die section 14c that is moveable inside the deforming tube 11 to cause expansion of the deforming tube 11 and a flaring die section 14d that is moveable relative to the deforming tube 11 to cause further expansion and tearing of a first end 12 of the deforming tube 11. The assembly may include a buffer pad 24 that is connected to an anchor member 17 by a tensioning member 23 made up of a telescopic tube assembly. The device is suitable for trains or other railway applications, but may also be used in other automotive, aerospace, or specialist transport vehicles.

Description

AN ENERGY ABSORPTION ASSEMBLY

The invention relates to an energy absorption assembly and a related method of its operation. The invention is of relevance in the field of crash energy management in e.g. railway applications. The invention is potentially of relevance to other situations in which crash energy absorption is required. Examples include crashes involving road vehicles and vehicles such as cranes, draglines, aerospace or other specialist transport vehicles, and land vehicle trains. The primary use of the invention however is in the railway industry.

Railway vehicles are subject to strict crashworthiness regulations, which deal with railway passive safety. Standards such as BS EN 15227 and 12663 (British standard GMRT2100) detail the railway vehicles' crashworthiness requirements. The energy absorption requirements are quantified by specifying that an approaching train unit must be able to maintain its integrity (and avoid overriding and derailment) when colliding with a stationary similar train unit at 36 km/h. BS EN 12663 constrains the maximum loads which energy absorbers might transmit to the different railway vehicle structures to up to 2000 kN, depending on the vehicle category.

Typically, energy absorbers which dissipate energy by means of plastic deformation, fracture and friction are employed to dissipate the kinetic energy of colliding railway vehicles. These energy absorbers are typically installed at the leading front of a railway rake or between vehicles. In a crash situation the energy absorbers experience a force that acts perpendicular to the front face of the vehicle, and typically is aligned with the longitudinal axis of the energy absorber. Transverse loads too can arise due to wheel wear, pitching, differences of vertical loads etc. The standard requires an offset of at least 40mm to be considered.

Existing solutions, such as splitting tubes and deforming tubes, provide energy absorption capabilities respectively by means of tearing and radial deformation of tubes.

These tubes are typically made of steel or aluminium alloys, although other materials have been used.

In many applications the ideal energy absorber exhibits a constant force-displacement response when subjected to axial loading. The expansion tubes are ideally suited to these applications since they can absorb energy whilst exhibiting near constant force-displacement characteristics. However, they suffer from poor stroke efficiency as they may crush only approximately 40% of the initial length of the device. Splitting tubes do not exhibit such a constant force as two peaks are present (corresponding to the initial tearing of the tube and to the contact between the formed "petals" and the tube). They do however exhibit high stroke efficiency as they may crush approximately 75% of the initial length of the device.

A deforming tube in essence is a hollow cylinder that is secured at one end to e.g. a buffer beam or another frame member of a railway vehicle so that the tube protrudes forwardly or rearwardly from the vehicle.

One end of a circular die is inserted in the protruding end of the tube. The die includes a buffer plate on its exterior surface lying remote from the tube. The die is typically tapered or otherwise of non-constant diameter. The inserted end of the die is a snug fit inside the tube.

The buffer plate is contacted by the plate of another buffer in the event of a crash. The crash energy drives the die further into the tube. The taper of the latter causes a length of the die that is of greater diameter than the interior of the tube to move into and along the latter.

Such movement of the die causes expansion of the tube as the die moves relative to it. The action of expanding the tube causes dissipation of the crash energy.

US 6523873 discloses an energy absorption system in which a tube provides both deforming and splitting responses to crash forces. The die is a hollow element that fits over the deforming tube. Crash energy causes the tube to be fed into the die. The shape of the die reduces the diameter of the tube.

The tube is formed with initiators of tears that propagate along the tube, as the die moves along it, to form petals that curl up along the length of the tube. The die is formed with apertures to permit the petals to extend from within the die to its exterior.

A disadvantage of the energy absorption system of US 6523873 derives from the fact is that it is intended for use with a motor vehicle. As a result the die is fixed in use to a beam or other chassis component of the vehicle; and the end of the tube that lies remote from the die is secured to a vehicle bumper.

In consequence of this arrangement any bending moment resisted by the energy absorption assembly during a crash is applied at the end of the tube at which deforming occurs, i.e. the location along the tube that is least able to provide effective bending moment resistance. It is believed that the energy absorption assembly of US 6523873 cannot be mounted in any other configuration because of the limited space inside a road vehicle bumper.

Also the assembly of US 6523873 requires a complex die shape that is expensive to manufacture; and the assembly is susceptible to problems caused by rotation of the deforming tube relative to the die.

In particular in this regard it is essential in the arrangement of US 6523873 that formation of the petals initiates such that the petals extend through the apertures. Any rotation of the parts of the assembly relative to one another may cause mis-alignment of the petals and the apertures with the result that the die may bind onto the tube. This in turn would mean that crash forces are transmitted to the vehicle, without any appreciable energy attenuation occurring.

According to the invention in a first aspect there is provided an energy absorption assembly comprising a hollow deforming tube; and a dual-function die including an expansion die section that is moveable inside the deforming tube to cause expansion of the deforming tube and a flaring die section that is moveable relative to the deforming tube to cause further expansion and tearing of a first end of the deforming tube.

Such an assembly differs from that of US 6523873 among other reasons because the deforming action causes enlargement (expansion) of the deforming tube, as opposed to crushing of it. This in turn means that both functions of the dual-function die may be effected by having the die move inside the deforming tube, with the advantage that the petals will correctly form regardless of the relative rotational orientations of the die and the deforming tube.

It is desirable to prevent rotation of the die and the deforming tube for other reasons, associated with operation of anti-climb features described below; but preventing rotation in order to assure adequate energy dissipation is not necessary in the assembly of the invention.

Also the shape of the die in the assembly of the invention is simpler, and hence easier to manufacture reliably, than the die of US 6523873.

The action of the die of the invention in moving inside the deforming tube means that deformation of the tube can readily be made to occur at the end of the deforming tube at which the crash loading is applied. This in turn minimises the bending moment applied, during a crash, in the vicinity of the deformed part of the tube. This in turn helps to assure the stability of the assembly of the invention.

Preferably the expansion die section and the flaring die section are secured one to another. More preferably the expansion die section and the flaring die section are sub-sections of a common dual-function die component. Such a component is advantageously straightforward to manufacture, has no moving parts or sections that could be disassembled, and is simple in operation.

Equally it is possible to devise embodiments of the invention in which a dual-function die is made up from two distinct die parts that are secured one to another.

Yet a further possibility, within the scope of the invention, is for the expansion die section and the flaring die section to be constituted as separate die components.

Preferably the hollow deforming tube is of circular cross-section and the expansion die section is a conical or truncated conical member a part of which defines a diameter that corresponds to an internal diameter of the deforming tube. Thus the assembly of the invention may include a die section that fits inside the deforming tube, and a further section of greater diameter and defined by the conical or truncated conical nature of the expansion die, that on movement of the expansion die inside the deforming tube irons the wall of the deforming tube to an enlarged diameter compared with its starting diameter.

Also preferably the average diameter of the flaring die section is greater than the average diameter of the expansion die section; and optionally the hollow deforming tube tapers from a relatively large diameter section at a free end adjacent the flaring die section to a relatively small diameter section spaced from the relatively large diameter section along the deforming tube. Such features allow the deforming tube to accommodate the two die sections in an efficient manner that minimises the risk of the dual-function die being driven off-centre.

In one embodiment of the invention the deforming tube is of substantially constant profile (cross-section) over at least a major part of its length. In particular the deforming tube may be of circular cross-section. Other, regular cross-sectional shapes however are also possible within the scope of the invention.

In alternative embodiments of the invention the deforming tube may be of non-constant cross-section. Thus e.g. the thickness of a wall of the deforming tube may vary from place to place along its length. Preferably the expansion die section and the flaring die section are positioned relative to one another so as to induce a step change in the force absorption characteristic of the energy absorption assembly part-way through deformation of the deforming tube.

For the avoidance of doubt the invention includes within its scope an arrangement in which the expansion die section is received inside the deforming tube.

Conveniently the flaring die section is or includes a circular die in which a relatively small diameter die part blends to a relatively large diameter die part by way of a flare having a curved profile. However other designs of flaring die section are possible within the scope of the invention.

Further conveniently the hollow deforming tube is of circular cross-section and the relatively large diameter part of the flaring die section is of a corresponding diameter to an internal diameter of the deforming tube. Thus the dual-function die may be arranged to be a snug fit in the deforming tube. This assures alignment of the die and the deforming tube, in turn maximising the extent to which the energy absorption during use of the assembly of the invention is constant and predictable.

Preferably the deforming tube includes, at the first end, one or more initiators of tearing.

The assembly may optionally include a plurality of such initiators (and especially six initiators) of tearing at equally spaced intervals about the periphery of the first end of the deforming tube.

The or each initiator of tearing may be or may include a notch in the material of the deforming tube.

The assembly of the invention may include one or more rotation preventers connecting the hollow deforming tube and the expansion die section. Alternatively the assembly may include one or more rotation preventers connecting the hollow deforming tube and the flaring die section. Preventing rotation of the dual-function die and the deforming tube is desirable as noted primarily in order to ensure that anti-climb features forming part of the energy absorption assembly are maintained in the correct orientation for operation.

In a particularly convenient arrangement the or each rotation preventer may include a protuberance protruding from an external surface of the expansion die section or the flaring die section and received in a said notch. Thus the initiators of tearing may have a secondary function in preventing rotation of the parts of the assembly relative to one another.

The flaring die section optionally may include a buffer pad that lies on the opposite side of the dual-function die from the deforming tube. Preferably the buffer pad includes formed on an external surface one or more anti-climb features. Such features may include e.g. horizontally extending, elongate ridges and recesses that combine with comparable features on the pad of an adjacent buffer. Such features are known per se in the buffer art.

Preferably the deforming tube includes an end that is remote from the dual-function die and that terminates in an anchor member. This aspect of the invention advantageously permits the inclusion of a tensioning member interconnecting the buffer pad and the anchor member inside the deforming tube. Thus it is possible beneficially to apply a pre-load, using the tensioning member, to the dual-function die inside the deforming tube.

The tensioning member desirably may take the form of a telescopic series of interconnected tubes. The tensioning member thus may be made adjustable in length and thereby capable of accommodating compression of the assembly in use as described herein.

Preferably the assembly of the invention includes a second end, opposite the first end, that is securable to an element of a railway vehicle. The term "element" as used herein includes e.g. a frame or chassis member of a vehicle, or a buffer beam.

The invention is also considered to reside in a railway vehicle including an energy absorption assembly as defined herein.

In a further aspect of the invention there is provided a method of absorbing impact energy, using an energy absorption assembly according to the invention as defined herein, including causing movement of the expansion die section inside the deforming tube to cause expansion of the deforming tube; and causing movement of the flaring die section relative to the deforming tube to cause further expansion and tearing of an end of the deforming tube.

Preferably tearing of an end of the deforming tube includes the initiation and curling, outside the deforming tube, of petals of the material of the deforming tube. Further preferably the curling of petals outside the material of the deforming tube includes contact between one or more curling petals and the material of the deforming tube.

There now follows a description of preferred embodiments of the invention, by way of non-limiting example, with reference being made to the accompanying drawings in which: Figure 1 is a perspective view, taken from one end and at an angle, of an energy absorption assembly according to the invention; Figure 2 is a transversely sectioned view of the assembly of Figure 1; Figure 3 is a perspective view of the Figure 1 energy absorption assembly taken from the opposite end to Figure 1 and showing the assembly after the initiation of energy absorbing deformation and tearing; Figure 4 is a longitudinal cross-sectional view of the assembly of Figure 3; Figure 5 is a view similar to Figure 3, showing the assembly of the invention in its most compressed state, corresponding to the end of a process of deformation and tearing; Figure 6 is a longitudinal cross-sectional view of the assembly of Figure 5; Figure 7 is a plot of the force response of the assembly of Figures 1 to 6 against the displacement (i.e. degree of compression), and including comparisons with energy absorbers not forming part of the invention as claimed; and Figure 8 is a perspective view showing the assembly of Figures 1 to 6 prior to the application of a pre-tensioning load through use of a tensioning member.

Referring to the drawings an energy absorption assembly 10 comprises a deforming tube 11 that in the embodiment shown is a hollow circular cylinder of a deformable material such as but not limited to a steel or an aluminium alloy. Deforming tube 11 is in an initial state of constant cross-section along most of the length of the energy absorption assembly 10, which as illustrated is elongate.

The deforming tube 11 may adopt cross sections other than the circular one shown.

At a first end 12 the diameter of the deforming tube is greater than over the remainder of the length of the tube 11. This enlarged diameter part 12 of the deforming tube 11 is connected to the remainder by way of a smooth taper 13.

A dual-function die 14 is formed of a material (such as a steel) that is sufficiently hard as to cause deformation of the material of the deforming tube 10 when driven as described below inside the deforming tube 10 by forces resulting from a vehicle crash.

The dual-function die 14 is of circular transverse cross-section and at one end is formed with a relatively small diameter section 14a as illustrated.

The small diameter section 14a connects to an intermediate diameter section 14b by way of a taper 14c. The profile of the sections 14a and 14b and the taper 14c correspond to the shape of the interior of the deforming tube 11 with the result that the sections 14a, 14b may be received inside the deforming tube as best shown in Figure 2.

Intermediate diameter section 14b of dual-function die 14 is of constant cross-section and blends into a flaring die section 14d. In flaring die section 14d the diameter of the dual-function die 14 increases according to a curved (especially but not necessarily part-circular) profile as illustrated. The outer extremity 14e of the flaring die section is a circular perimeter that represents the largest-diameter part of the dual-function die 14.

The dual-function die 14 thus is part-conical and is truncated at one end. It could however in other embodiments of the invention be formed as a conical member, although this probably would result in sub-optimal performance at the end of the movement of the dual-function die 14 described below.

As is apparent from the figures the parts of the dual-function die 14 are secured to one another and indeed in the preferred embodiment of the invention illustrated are formed integrally with one another. This may be achieved e.g. by machining the dual-function die 14 from a single piece of metal; by fabricating the die 14 in separate pieces and securing them together e.g. by welding or using an adhesive bond; or by casting the dual-function die 14.

In an alternative arrangement however the parts of the dual-function die 14 do not need to be permanently secured to one another, it being sufficient in some embodiments of the invention simply for the parts of the dual-function die 14 to transmit crash energy from the exposed end of the dual-function die 14 to the deforming tube 11 in the manner described below.

At its end 16 opposite end 12 deforming tube 11 would be open but for the presence of an anchor member in the form of a mounting plate 17 secured by way of an annular weld 18 to terminate and close the end of the tube 11.

In the embodiment shown the mounting plate 17 is essentially square, although other shapes and sizes than that shown are possible within the scope of the invention. The size of the mounting plate 17 is chosen to provide for stable support of the deforming tube when the mounting plate 17 is in use bolted via bolt holes 19 to e.g. a buffer beam or another frame or chassis member of a vehicle, especially a railway vehicle.

The arrangement of the mounting plate 17 and the bolt holes 19 is such as to permit the deforming tube in its un-deformed condition shown in Figures 1 and 2 to protrude perpendicular to a buffer beam, etc., to which the mounting plate 17 is bolted.

The deforming tube 11 includes formed at regularly spaced intervals about the periphery of end 12 a plurality of tear initiators in the form of notches or cuts 22 extending longitudinally a short distance along the deforming tube 12.

The preferred embodiment of the invention illustrated includes six such notches or cuts 21 as the inventors have determined that this is an optimal number. Other numbers and patterns of tear initiators however are possible within the scope of the invention.

Moreover the tear initiators do not need to adopt the notch/cut form shown; and indeed may be absent entirely from some embodiments of the invention.

The assembly 10 of the invention may include one or more features (not shown in the figures) that prevent rotation of the dual-function die 14 relative to the deforming tube during operation of the assembly 10 to attenuate crash forces. Such features may include e.g. one or more protuberances protruding from the intermediate diameter section 14b of the dual-function die 14. Such protuberances may be received in the notches or cuts 21 thereby preventing relative rotation between the main parts of the assembly. As noted above this is advantageous in terms of maintaining anti-climbing features 26, 27 at an operative orientation.

The dual-function die 14 includes formed extending therethrough a central bore 22. A tensioning member in the form of an elongate, segmented telescopic tube assembly 23 is rigidly secured at one end 23a to the mounting plate 17 and protrudes at opposite end 23b via the bore 22 from the opposite side of dual-function die 14 to that of small diameter section 14a.

Telescopic tube assembly 23 is formed of a series of elongate telescoping segments 23c, 23d, 23e, 23f received one inside another in the manner of the sections of a telescope. The otherwise free end 23b of the segment 23e located furthest from mounting plate 17 is anchored e.g. by means of co-operating thread parts in a buffer pad 24 secured on the exterior of dual-function die 14 on the side remote from small diameter section 14a.

The segments 23c -23f are slideable one relative to another and include limit features that prevent them from being separated from one another. Adjustment of the anchoring of the end 23b in the buffer pad 24 therefore causes tensioning of the telescopic tube assembly in the longitudinal direction. The ability of the segments 23c -23f to slide relative to one another on the other hand means that on the application of a compressive crash force to the energy absorbing assembly 10 the telescopic tube assembly may readily and controlledly collapse to a shortened configuration.

The segments 23c, 23d and 23e are formed from e.g. a steel as hollow members. Segment 23f is a solid member as illustrated, but the invention is not limited to the precise combination of segments shown.

Regardless of the precise design of the tensioning member its purpose is to apply a tensile pre-load to the dual-function die 14. Aside from the fact that this beneficially prevents the dual action die 14 from separating from the deforming tube 11 the pre-load makes the start force in any crash energy absorption situation more predictable. As is known in the art a predictable buffer start force value is generally advantageous.

The buffer pad 24 as illustrated is formed to include on its in-use exposed surface a series of horizontally extending ridges 26 and interposed depressions 27 that amount to anti-climb features.

The principles of such features are known in the buffer art.

The figures show four elongate ridges 26 and three interposed, elongate depression 27; but other numbers and patterns of anti-climb features are possible within the scope of the invention.

The anti-climb features illustrated operate during a crash situation by engaging similar features formed on the exterior of a buffer or other energy absorber of a vehicle adjacent the one on which the assembly 10 is mounted. It is desirable in order for the anti-climb features to function correctly that the buffer pad 24 does not rotate in use of the assembly 10 relative to the deforming tube 11 or indeed a buffer beam to which the assembly 10 is secured.

The anti-rotation protuberances described above together with the non-rotative securing of the mounting plate 17 assure that the anti-climb features remain correctly aligned during compression of the assembly 10.

Figures 1 and 2 show the energy absorption assembly 10 in the pre-use configuration as may exist when the assembly 10 is mounted on a railway vehicle buffer beam. Figures 2 to 6 illustrate the assembly 10 at various stages following initiation of a crash.

At the start of absorption of the energy of a crash the dual-function die 14 moves under the influence of the crash force inside the deforming tube 11. During this initial stage the taper 14c of the die 14 irons the wall of the deforming tube 11 such that the taper 13 therein travels along the deforming tube in the same direction as the die 14. The diameter of the thus ironed length of the deforming tube 14 becomes similar to that of the tube end section 12.

Such action attenuates some crash energy. The action of ironing of the wall of deforming tube 14 gives rise to a generally predictable start force in the energy absorption process. The existence of pre-load tension provided by the tensioning member 23 as noted assists in providing a predictable start force.

After a short period of travel the end section 12 of the deforming tube 14 engages the curved part 14d of the flaring die section. This causes further enlargement of the diameter of the deforming tube 14. Assisted by the notches 21 when these are present, tearing of the material of the tube 14 to form individual petals 11a takes place. When the notches 21 are provided the number of resulting petals of metal equates to the number of notches, and the petals 11a are evenly distributed about the periphery of the deforming tube 11.

As the petals lla form they curl around the flaring die curve 14d and roll back towards the remainder of the deforming tube 14. This condition is illustrated in Figures 3 and 4, and corresponds to an increase in the load exerted by the assembly 10 and hence an increase in the attenuated crash force.

Further forming of the petals 1 la causes them to contact the outer wall of the deforming tube 14 as the diameter of each rolled petal 11a increases. This causes a momentary increase in the force attenuation. This increase reduces once initial contact of the petals 11 a with the tube wall has occurred. Thereafter a generally steady state situation exists, with constant force attenuation until the tube 14 is compressed as much as possible (i.e. when the dual-function die 14 contacts the mounting platel7). This is illustrated in Figures 5 and 6.

Throughout compression of the assembly 10 the tensioning member 23 gradually collapses onto itself as shown in Figures 4 and 6.

The force at which the deforming tube 11 deforms is governed by its wall thickness. A constant wall thickness results in a near-constant deforming force in the expanding phase. The splitting phase is less constant but still governed by the thickness of the tube. The deforming tube wall thickness can be varied or profiled along the longitudinal axis to control the magnitude of the resisting force offered by the deforming tube 11 as it is expanded and split by the dual-function die 14. In this way the shape of force-displacement characteristic can be varied to suit the application.

It is also possible to arrange the assembly 10 to have a step change in the force part way through the deformation of the device by arranging the relative position of the expansion die section 14c and the flaring die section 14d, such that the flaring die section 14d contacts the tube 11 part way through the deformation.

The radial expansion stage dissipates energy by means of plastic deformation and heat generation due to the circumferential stretching of the deforming tube 11 as the die 14 slides into the tube. Friction and heat generation between the deforming tube 11 and die 14 surfaces in contact adds to the dissipation of energy.

The splitting stage dissipates energy by means of plastic deformation and heat generation caused by: 1) stretching of the expanded tube 11 as it comes into contact with the flaring/splitting section 14d of the die 14; 2) unstable plastic deformation and tearing of the tube 11 in the vicinity of the notches 21; 3) bending of the formed strips/petals 11a as they curl; 4) unbending of the original circular strips/petals 11a into flat strips; and 5) friction between the tube 11 and the splitting/flaring die 14d.

Figure 7 plots the force dissipated by the assembly 10 against longitudinal compression (referred to as "displacement" in Figure 7). If Figure 7 the solid line represents the performance of an assembly according to the invention; the dashed line an absorption assembly that operates using a tube splitting or tearing effect alone; and the dotted line the performance of an energy absorber that operates using tube expansion (wall ironing) alone.

Referring to the solid line plot, at the commencement of ironing of the deforming tube as represented by numeral 23 the dissipated force increase steadily as the die 14 becomes fully seated in the deforming tube 11. The absorbed force rises rapidly, at numeral 29, as tearing of the deforming tube 14 commences.

The force reduces to an essentially steady state value as represented by numerals 31 and 33, with a force peak at numeral 32 as the petals contact the exterior of the deforming tube as described above.

Comparison of the solid line plot of Figure 7 with the dotted line shows that although the profile of the performance plot of a tearing tube energy absorber in some ways is similar to that of the energy absorber of the invention, the average force is lower than in the case of the invention.

The dotted line plot in Figure 7 shows that an absorber operating through tube wall deformation alone, without any tearing, produces a very steady force attenuation with predictable starting force performance that is similar to that of the invention.

The energy absorption assembly of the invention provides acceptably predictable performance with a high energy attenuation value and good use of the deforming tube length available. Moreover the dual-function die 14 provides a good degree of overlap inside the deforming tube 11 with the result that the assembly 10 exhibits good stability even when off-centre forces are experienced.

The overall arrangement of the assembly 10 of the invention means that the deformation of the deforming tube 14 takes place at a location remote from the mounting plate 17. This also reduces instability of the assembly in use as the maximum bending moment is generated at a location remote from the zone of deformation of the deforming tube 10.

The invention overcomes the main weaknesses of the splitting-alone and expansion-alone devices working independently. The stroke efficiency, that is the ratio of the stroke to the initial length of the energy absorber, is approximately 40% for expansion-alone devices, whereas it is 70% and 75% for the invention and the splitting-alone devices respectively. Therefore, for a similar initial length, the invention and the splitting-alone devices can achieve longer strokes.

The force efficiency, that is the ratio of the peak load to the mean load, which measures the amount of energy dissipated by an energy absorber given a limit maximum operating load, is 100%, 80% and 90% for the expansion-alone, splitting-alone and invention assemblies respectively. The invention is more force-efficient than the splitting-alone device as the inclusion of the expansion stage gives it more control over the mean load of the energy absorber. The peak load of the invention is proportionally smaller compared its mean load than the peak load of the splitting-alone device compared to its mean load.

An energy absorption efficiency may be calculated by combining the stroke efficiency and force efficiency of the energy absorbers.

Figure 8 shows the main components of the assembly 10 during manufacture, before a pre-load is applied using the tensioning member 23.

The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention.

Claims

CLAIMS1. An energy absorption assembly comprising a hollow deforming tube; and a dual-function die including an expansion die section that is moveable inside the deforming tube to cause expansion of the deforming tube; and a flaring die section that is moveable relative to the deforming tube to cause further expansion and tearing of a first end of the deforming tube.
2. An energy absorption assembly according to Claim 1 wherein the expansion die 1 o section and the flaring die section are secured one to another.
3. An energy absorption assembly according to Claim 1 or Claim 2 wherein the expansion die section and the flaring die section are sub-sections of a common dual-function die component.
4. An energy absorption assembly according to Claim 1 or Claim 2 wherein the expansion die section and the flaring die section are constituted as separate die components.
5. An energy absorption assembly according to any preceding claim wherein the hollow deforming tube is of circular cross-section and the expansion die section is a conical or truncated conical member a part of which defines a diameter that corresponds to an internal diameter of the deforming tube.
6. An energy absorbing assembly according to Claim 5 wherein the hollow deforming tube tapers from a relatively large diameter section at a free end adjacent the flaring die section to a relatively small diameter section spaced from the relatively large diameter section along the deforming tube.
7. An energy absorbing member according to any of Claims 1 to 5 wherein the deforming tube is of substantially constant cross-section.
8. An energy absorption assembly according to any of Claims 1 to 6 wherein the deforming tube is of non-constant cross-section.
9. An energy absorption assembly according to any preceding claim wherein the expansion die section and the flaring die section are positioned relative to one another so as to induce a step change in the force absorption characteristic of the energy absorption assembly part-way through deformation of the deforming tube.
10. An energy absorption assembly according to any preceding claim wherein the expansion die section is received inside the deforming tube.
11. An energy absorption assembly according to any preceding claim wherein the flaring die section is or includes a circular die in which a relatively small diameter die part blends to a relatively large diameter die part by way of a flare having a curved profile.
12. An energy absorption assembly according to Claim 11 wherein the hollow deforming tube is of circular cross-section and wherein the relatively large diameter part of the flaring die section is of a corresponding diameter to an internal diameter of the deforming tube.
13. An energy absorption assembly according to any preceding claim wherein the deforming tube includes, at the first end, one or more initiators of tearing.
14. An energy absorption assembly according to Claim 12 including a plurality of initiators of tearing at equally spaced intervals about the periphery of the first end of the deforming tube.
15. An energy absorption assembly according to Claim 13 or Claim 14 including six initiators of tearing.
16. An energy absorption assembly according to any of Claims 13 to 15 wherein the or each initiator of tearing is or includes a notch in the material of the deforming tube.
17. An energy absorption assembly according to any preceding claim including one or more rotation preventers connecting the hollow deforming tube and the expansion die section.
18. An energy absorption assembly according to any of Claims 1 to16 including one or more rotation preventers connecting the hollow deforming tube and the flaring die section.
19. An energy absorption assembly according to any preceding claim depending from Claim 16 wherein the or each rotation preventer includes a protuberance protruding from an external surface of the expansion die section or the flaring die section and received in a said notch.
20. An energy absorption assembly according to any preceding claim wherein the flaring die section includes a buffer pad that lies on the opposite side of the dual-function die from the deforming tube.
21. An energy absorption assembly according to any preceding claim wherein the deforming tube includes an end that is remote from the dual-function die and that terminates in an anchor member.
22. An energy absorption assembly according to Claim 21 when dependent from Claim 18 including a tensioning member interconnecting the buffer pad and the anchor member inside the deforming tube.
23. An energy absorption assembly according to Claim 22 wherein the tensioning member is or includes a telescopic series of interconnected tubes.
24. An energy absorption assembly according to Claim 20 or any preceding claim depending therefrom wherein the buffer pad includes formed on an external surface one or more anti-climb features.
25. An energy absorption assembly according to any preceding claim including a second end, opposite the first end, that is securable to an element of a railway vehicle
26. A railway vehicle including an energy absorption assembly according to any preceding claim.
27. A method of absorbing impact energy, using an energy absorption assembly according to any preceding claim, including causing movement of the expansion die section inside the deforming tube to cause expansion of the deforming tube; and causing movement of the flaring die section relative to the deforming tube to cause further expansion and tearing of an end of the deforming tube.
28. A method according to Claim 25 wherein tearing of an end of the deforming tube includes the initiation and curling, outside the deforming tube, of petals of the material of the deforming tube.
29. A method according to Claim 26 wherein the curling of petals outside the material of the deforming tube includes contact between one or more curling petals and the material of the deforming tube.
30. An energy absorption apparatus generally as herein described, with reference to and/or as illustrated in the accompanying drawings.
31. A method generally as herein described, with reference to and/or as illustrated in the accompanying drawings.
32. A railway vehicle generally as herein described.