TECHNOLOGICAL FIELD

The presently disclosed subject matter is related to the field of load limiters, and in particular, to load limiters including telescopic assemblies.

BACKGROUND

Load limiters, shock absorbers, and other mechanisms for absorbing energy and limiting loads are known in the art. For example, they are widely used in vehicles which move at speed, such as cars and planes, to protect mechanical parts, passengers and/or cargo from excessive loads to which they can be exposed, for example, during an emergency collision, when a vehicle undergoes extreme deceleration over a short period of time.

The field of application for these mechanisms is as broad as the field which includes all bodies which move at speed, and which will undergo planned or emergency deceleration - elevators, automobiles, trains, planes, spacecraft, etc.

Known mechanisms include, for example, US 4,361,212 which discloses a bidirectional mechanical load limiter for a push-pull control linkage, which includes a tubular crushable core that crushes in response to a predetermined tensile or compressive load in order to limit the load in the linkage.

Another example, US 4,558,837 discloses skid landing gear provided with components having a device for absorbing energy by plastic deformation and/or for limiting stress.

Yet another example, US 3,461,740 discloses a collapsible column of the type used for steering motor vehicles, having means for absorbing energy arranged about the shaft sections such that the column absorbs energy while telescoping upon impact to avoid chest injuries to a driver involved in an accident.

Yet another example, US 2981534 discloses a telescopic shock absorber comprising a cylinder and a piston rod, and a resilient cushion fitted on the piston rod so as to operate in parallel therewith. Yet another example, GB 2446662 discloses a suspension system including two opposite E-springs and a hydraulic damper.

Yet another example, DE 10247640 discloses a shock absorber arranged in combination with a spring such that the spring slides on a piston rod of the shock absorber during a compression movement.

Yet another example, DE 19956090A1 discloses a shock absorber attached to leaf springs via a support bearing and an attachment point.

Yet another example, DE 19962026 A 1 discloses a spring assembly including a damper element, a piston rod, and a spring element.

Yet another example, RU 2524712 discloses a disposable absorber comprising collapsing elastic damping elements.

Yet another example, RU 2552426 discloses a shock absorber for explosion- proof objects comprising elastic-damping elements.

Yet another example, US 4828237 discloses a hydraulic shock absorber comprising a sleeve telescopically attached to a cylinder movable axially outwardly therefrom to increase effective radial load bearing support.

Yet another example, US 7823709 discloses bellows for cylinder units to provide protection against dirt and damage.

Yet another example, US 9004470 discloses a shock absorber including a jounce bumper nose retaining feature which interacts with a jounce bumper to eliminate sliding and noise.

Yet another example, US 2006071378 discloses a suspension assembly including includes a first end member, a second end member and a flexible member defining a fluid chamber together with said first and second end members.

Yet another example, WO 2010064291 discloses an electromagnetic suspension system comprising an air spring that acts as a suspension mechanism.

Yet another example, WO 2011026549 discloses a spring-and-shock absorber element comprising a spring and a spring bearing provided with a passage to allow sliding of a piston rod there-through.

Yet another example, CN 202520849 discloses a vehicle vibration absorber comprising an air spring and a damper. GENERAL DESCRIPTION

In accordance with one aspect of the presently disclosed subject matter, there is provided a load limiter, comprising a telescopic assembly having a longitudinal axis. The telescopic assembly has a first member, and a second member at least partially introduced into the first member and configured for sliding displacement with respect to the first member along the longitudinal axis upon application of a load to at least one of the first and second members at least partially along the longitudinal axis.

The load limiter further comprises at least one energy absorbing element having a first end connectable to the first member and a second end connectable to the second member so that the energy absorbing element is disposed at least partially externally to the telescopic assembly. The energy absorbing element has an initial shape in which its first end and its second end are spaced at a distance from one another, and the shape of the energy absorbing element is configured for deforming upon application of the load while the distance varies, thereby absorbing at least part of the energy of the load.

The second member of the telescopic assembly can be configured to be displaced with respect to the first member, between a first position in which the energy absorbing element has its initial shape and the distance between the first end and the second end is a first distance, and at least one of a second position and a third position.

In the second position, the second member can be displaced into the first member and introduced therein to a greater extent than in the first position, and the energy absorbing element has a compressed shape in which the first end and the second end of the energy absorbing element are spaced from one another at a second distance which is shorter than the first distance.

In the third position, the second member can be displaced into the first member and introduced therein to a lesser extent than in the first position, and the energy absorbing element has an extended shape, in which the first end and the second end of the energy absorbing element are spaced from one another at a third distance which is longer than the first distance.

The energy absorbing element can further have an inner surface facing an imaginary line extending between the first end and the second end, on which a farthest point from the imaginary line is located at a first height from the imaginary line when the energy absorbing element has its initial shape; and wherein when the energy absorbing element has its compressed shape, the farthest point is spaced from the imaginary line at a second height which is greater than the first height, and when the energy absorbing element has its extended shape, the farthest point is spaced from the imaginary line at a third height which is smaller than the first height.

The energy absorbing element further has an outer surface facing away from the imaginary line, which, in the initial shape of the energy absorbing element, can have a lesser curvature than the inner surface.

The energy absorbing element can further have a main axis extending between its first end and its second end, and cross-sections taken perpendicularly to this main axis that can have varying cross-sectional areas.

The cross-sectional area at the farthest point of the energy absorbing element can be greater than at each of the first end and the second end of the energy absorbing element.

The cross-sectional area at the farthest point of the energy absorbing element can be maximal with respect to all cross-sectional areas of all other cross-sections along the main axis of the energy absorbing element.

Each of the cross-sections can have a cross-sectional height extending along an imaginary plane including the imaginary line and a cross-sectional width extending along a plane perpendicular to the imaginary plane. The cross-sectional width in all of the cross-sections can be constant and the cross-sectional height can be varying.

The cross-sectional height of a cross-section including the farthest point can be maximal with respect to the cross-sectional heights of all the other cross-sections along the main axis of the energy absorbing element.

Each of the cross-sections can have a substantially rectangular or elliptical shape.

The variation in the area of the cross-sections along the main axis of the energy absorbing element, can allow substantially uniform stress and strain to develop throughout the energy absorbing element when the load is applied. The energy absorbing element can be designed to be thicker where axial loads on the load limiter can be expected to cause maximal bending moment and maximal stress, i.e. at the farthest point, and the stress is consequently distributed substantially uniformly throughout the element when the load limiter is loaded. This can result in the energy absorbing element having a substantially uniform plastic deformation along its length when the load is applied, as opposed to the formation of a plastic hinge (which does not occur in the presently disclosed subject matter). Such a plastic hinge is formed when stress becomes concentrated in one location of a loaded element, and as a result extreme deformation occurs at that spot, resulting in a hinge effect, while the other parts of the element do not participate in the task of energy absorption, undergo little or no stress, and little or no deformation. Whereas the plastic deformation occurring in the area of a plastic hinge is inefficient and dangerous, as it is a large amount of stress and strain occurring over a small area, the plastic deformation which occurs over the energy absorbing element of the presently disclosed subject matter, is equivalent to the summation of small amounts of plastic deformation occurring over the entire element, and thus is highly efficient. The plastic deformation undergone by the element is maximal, i.e. the displacement undergone by the element is maximal, i.e. energy absorption is maximized.

The formation of a plastic hinge in a structural element such as the energy absorbing element provided in accordance with the presently disclosed subject matter, can be dangerous in a situation where safety is dependent upon the integrity of the structural element, since the formation of a plastic hinge at a particular location in the element is an indication that structural failure is occurring at the location of the plastic hinge, and that breakage of the element at that location is very likely to be imminent if the element continues to be loaded. An area of each of the cross-sections along the main axis of the energy absorbing element is configured to vary in accordance with a calculated allowable bending moment for the energy absorbing element under design load at each of the cross-sections, such that the cross-sectional area is maximal at a location along the main axis where the bending moment is maximal, and such that the cross-sectional area decreases in size along the main axis proportionately in accordance with a reduction in values of the bending moment along the main axis.

In addition to being as opposed to a plastic hinge and elastic springs, the energy absorbing element provided in accordance with the presently disclosed subject matter is configured to undergo permanent deformation of at least 0.2% at beginning of the plastic deformation. For instance, the energy absorbing element undergoes at least 0.2% permanent deformation even at the beginning of the deformation (upon application of load), as opposed to elastic springs. Such elastic springs are meant to deform elastically, at least until a respective elastic limit is reached thereby exhibiting zero plastic deformation at least until such elastic limit is reached. The structural configuration of the energy absorbing element, including variable cross-sectional area along the length of the energy absorbing element and the cross-sectional height of the cross-section including the farthest point being greater than a cross-sectional width of the cross- section including the farthest point, enables the plastic deformation throughout the length of the energy absorbing element. The resultant permanent deformation being at least 0.2% signifies that for even an initial stress applied to the energy absorbing element, there would be at least 0.2% permanent strain experienced in the energy absorbing element upon removal of said stress.

The energy absorbing element can have a first leg with its first end, a second leg with its second end, and a bridging portion interconnecting the first leg and the second leg and forming together a curved shape.

The bridging portion together with the first leg and the second leg can form a continuous solid body.

The initial shape of the energy absorbing element can be a boomerang-like shape.

The initial shape of the energy absorbing element can be symmetrical.

The energy absorbing element can be disposed completely externally to the telescopic assembly.

The first end and the second end of the energy absorbing element can be pivotally connected to the first member and the second member, respectively, of the telescopic assembly.

It will be appreciated that due to the structural configuration of load limiter in accordance with the presently disclosed subject matter, i.e., the telescopic nature of telescopic assembly, the shape of energy absorbing elements, their composition of a ductile material having high elongation to break, and their disposition externally to telescopic assembly, as well as the pivotal nature of the pivotal connections between the ends of energy absorbing elements, and the first and the second members, the following desirable outcomes can be achieved with respect to the energy absorbing operation of load limiter:

the load path of the load applied to the load limiter acts in the axial direction only along the telescopic assembly, such that the telescopic assembly is unharmed after an energy absorption operation (compressive or tensile) of the load limiter. Thus, the load limiter remains in working order to absorb energy in subsequent strokes of load applied to it;

Upon application of a known load to the load limiter designed on the basis of design requirements (e.g., anticipated loads), to absorb a calculable amount of energy through a calculable displacement in tension and / or compression, the load limiter transmits only a calculable constant load, and prevents bending moments from being transmitted;

In their disposition external to the telescopic assembly, the energy absorbing elements are easily accessible for replacement when necessary;

The energy absorbing element undergoes permanent deformation of at least

0.2%;

The plastic deformation of the energy absorbing element allows achieving maximum allowable plastic strain along its entire length up to the end of the deformation process.

The load limiter of the presently disclosed subject matter can be mounted to landing gear of a spacecraft, or integrated with a steering column of a vehicle.

In accordance with another aspect of the presently disclosed subject matter, there is provided a vehicle comprising a load limiter according to the above first aspect, and with any of the above combinations and configurations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Fig. 1A is an isometric view of a load limiter according to one example of the presently disclosed subject matter;

Fig. IB is an isometric view of one of the energy absorbing elements of the load limiter shown in Fig. 1A;

Fig. 1C is a cross-section of the energy absorbing element of Fig. 1B, taken along line C-C shown in Fig. 1B; Fig. ID is a cross-section of the energy absorbing element of Fig. 1B, taken along line D-D shown in Fig. 1B;

Fig. IE is a cross-section of the energy absorbing element of Fig. 1B, taken along line E-E shown in Fig. 1B;

Fig. 2A is an isometric view of the load limiter shown in Fig. 1A, with the energy absorbing elements shown in their compressed shape;

Fig. 2B is an isometric view of one of the energy absorbing elements of the load limiter shown in Fig. 2A;

Fig. 3A is an isometric view of the load limiter shown in Fig. 1A, with the energy absorbing elements shown in their extended shape; and

Fig. 3B is an isometric view of one of the energy absorbing elements of the load limiter shown in Fig. 3A.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to Fig. 1A, illustrating a load limiter 10 according to one embodiment of the presently disclosed subject matter.

The load limiter 10 comprises a telescopic assembly 20 having a longitudinal axis Y, a first member 22 and a second member 24 at least partially introduced into the first member 22. The load limiter 10 further comprises two identical energy absorbing elements disposed at two opposite sides of the telescopic assembly 20, i.e., a first energy absorbing element 30 and a second energy absorbing element 30'. Explanations below are made with respect to the first energy absorbing element 30, however, they are similarly and respectively related to the second energy absorbing element 30'. The first energy absorbing element 30 has a first end 32 pivotally connected to the first member 22 and a second end 34 pivotally connected to the second member 24 so that the first energy absorbing element 30 is disposed externally to the telescopic assembly 20.

The load limiter 10 is structured so that second member 24 is configured for sliding displacement with respect to first member 22 along the longitudinal axis Y upon application of a load (i.e., a compressive load or a tensile load) to at least one of first and second members 22 and 24 at least partially along the longitudinal axis Y.

The first energy absorbing element 30 is structured to have an initial shape in which the first end 32 and the second end 34 are spaced at a distance from one another. The shape of first energy absorbing element 30 is configured to deform upon application of the above mentioned load, while the distance between the first end 32 and the second end 34 varies, i.e., increases or decreases, in accordance with the direction of the load, such that energy absorbing element 30 thereby absorbs at least part of the energy of the load.

In the example shown in Fig. 1A, two different exemplary loads are shown. The first example is a compressive load Fc applied to second member 24 of load limiter 10 along longitudinal axis Y. The second example is a tensile load FT applied to second member 24 of load limiter 10. As can be seen in Fig. 1 A, exemplary load FT is applied to second member 24 of load limiter 10 at an angle of a to longitudinal axis Y, such that the tensile load applied to second member 24 along the longitudinal axis Y is the vertical component of load FT, i.e., FTY = FT COS a. The direction of the compressive load and the tensile load shown in Fig. 1 A is exemplary only, and can of course vary.

Application of the compressive load Fc to load limiter 10 of Fig. 1A, would cause second member 24 to slide into first member 22 in the direction of the arrow shown to represent compressive load Fc in Fig. 1A. Application of the tensile load FT to load limiter 10 of Fig. 1 A, would cause second member 24 to slide further out of first member 22 in the direction of the arrow shown to represent FTY, the component of tensile load FT acting along the longitudinal axis Y of telescopic assembly 20.

In the example of load limiter 10 shown in Fig. 1A, the distance between first end 32 and second end 34 of the energy absorbing element 30 is shown to be a first distance Dl, and the corresponding shape of load limiter 10 shown in Fig. 1A is the initial shape of load limiter 10. The shape of energy absorbing element 30 is configured to deform upon application of a load, such as compressive load Fc or tensile load F _T , to at least one of first member 22 and second member 24, while the distance between first end 32 and second end 34 varies, such that first energy absorbing element 30 thereby absorbs at least part of the energy of the applied load.

As described previously with respect to Fig. 1A, second member 24 is configured to be displaced with respect to first member 22 of load limiter 10. In a first position of second member 24 with respect to first member 22, energy absorbing element 30 has its initial shape, in which the distance between first end 32 and second end 34 of energy absorbing element 30 is the first distance Dl. Upon application of the compressive load Fc, second member 24 is configured to be displaced with respect to first member 22 from the first position to a second position shown in Fig. 2A, and upon application of the tensile load F _T , second member 24 is configured to be displaced with respect to first member 22 from the first position to a third position shown in Fig. 3A. This displacement causes variation of the distance between first end 32 and second end 34 of energy absorbing element 30, accompanying its deformation.

An exemplary second position of second member 24 with respect to first member 22 is shown in Fig. 2A. In the second position, second member 24 is displaced into first member 22 and introduced therein to a greater extent than in the first position. Furthermore, in the second position, first energy absorbing element 30 has a compressed shape in which first end 32 and second end 34 are spaced from one another at a second distance D2 which is shorter than the first distance Dl.

Returning for a moment to the example of load limiter 10 shown in Fig. 1A, it can be seen that in the first position of second member 24 with respect to first member 22, wherein second member 24 is partially introduced into first member 22, a remaining portion of second member 24 not introduced into first member 22 has a length of Nl.

As explained above, in the second position of second member 24 with respect to first member 22 second member 24 is displaced into first member 22 and introduced therein to a greater extent than in the first position. This scenario would be expected in the event that a compressive load is applied to telescopic assembly 20. This can be seen in the example of load limiter 10 shown in Fig. 2 A, wherein exemplary compressive load Fc is seen to be applied to telescopic assembly 20. Consequently, second member 24 is seen to be displaced into first member 22 to a maximal extent, and the length N2, corresponding to length Nl of Fig. 1 , the remaining length of second member 24 not introduced into first member 22, is minimal. In the example shown in Fig. 2A illustrating the second position of second member 24 with respect to first member 22, it is apparent that N2 < Nl , and accordingly that second member 24 is displaced into first member 22 and introduced therein to a greater extent in the second position of Fig. 2A than in the first position shown in Fig. 1 A.

As explained above, when second member 24 is displaced from a first position (Fig. 1 A) to a second position (Fig. 2A), energy absorbing element 30 of load limiter 10 has a compressed shape, and the distance between its first end 32 and second end 34 is the second distance D2 which is shorter than the first distance Dl. The displacement AD undergone by the first and second ends of first energy absorbing element 30 during its deformative transition between its initial shape and its compressed shape (compressive displacement) is the difference between the lengths of Dl and D2, i.e. \ D 12 = Dl - D2.

An exemplary third position of second member 24 with respect to first member 22 of load limiter 10 is shown in Fig. 3 A. In the third position, second member 24 is displaced into first member 22 and introduced therein to a lesser extent than in the first position. Furthermore, in the third position of second member 24, first energy absorbing element 30 has an extended shape in which first end 32 and second end 34 are spaced from one another at the third distance D3 which is longer than the first distance Dl.

As explained above, in the third position of second member 24 with respect to first member 22, second member 24 is displaced into first member 22 and introduced therein to a lesser extent than in the first position. This scenario would be expected in the event that a tensile load is applied to telescopic assembly 20. This can be seen in the example of load limiter 10 shown in Fig. 3 A, wherein exemplary tensile load FT is seen to be applied to telescopic assembly 20. Consequently, second member 24 is seen to be displaced into first member 22 to a lesser extent than in Fig. 1A, since length N3, the remaining length of second member 24 not introduced into first member 22, is greater than length Nl in Fig 1A.

As explained above, when second member 24 is displaced from a first position (Fig. 1A) to a third position (Fig. 3A), energy absorbing element 30 of load limiter 10 has an extended shape, and the distance between its first end 32 and second end 34 is the third distance D3 which is longer than the first distance Dl. Accordingly, it can be seen in Fig. 3A that energy absorbing element 30 is in its extended shape, first end 32 and second end 34 having moved away from each other. As the separating distance between first end 32 and second end 34 has increased, as can be seen in Figs. 1A and 3 A, the third distance D3 is longer than the first distance Dl of Fig. 1A. Furthermore, the displacement AD undergone by energy absorbing element 30 during its deformative transition between its initial shape and its extended shape (tensile displacement) is the difference between the lengths of Dl and D3, i.e. \Di _¾ = D3 - Dl.

Reference is now made to Figs. 1B, 2B and 3B, which illustrate close-up views of first energy absorbing element 30, in its initial, compressed and extended shapes, respectively. As shown in Fig. 1B, first energy absorbing element 30 has an inner surface 40 facing an imaginary line L extending between first end 32 and second end 34 of energy absorbing element 30. Furthermore, energy absorbing element 30 has a farthest point P _F spaced from imaginary line L at a first height Hl when energy absorbing element 30 has its initial shape.

In comparison, as shown in Fig. 2B, when energy absorbing element 30 has its compressed shape, farthest point P _F is spaced from imaginary line L at a second height F12 which is greater than the first height Hl, and when the energy absorbing element has its extended shape, as shown in Fig. 3B, farthest point P _F is spaced from imaginary line L at a third height H3 which is smaller than first height Hl.

First energy absorbing element 30 is shaped and composed of a material such that it is configured to absorb a maximal amount of energy with a minimal amount of material. The objective achieved through a minimal use of material is the reduction in weight of the energy absorbing element. The optimization of the shape of first energy absorbing element 30 can thus also be seen as the optimization of the ratio between the energy absorption capacity of the energy absorbing element and its weight. Furthermore, the first energy absorbing element 30 has a monolithic structure, i.e., it is uniformly composed of a solid material throughout its volume, as shown in Figs. IB, 2B and 3B. The objective achieved through solid monolithic construction is better strength and durability of the energy absorbing element 30 while maintaining and enhancing its plastic deformability throughout its length.

In order to minimize the weight of energy absorbing element 30 by minimizing the amount of material used for energy absorbing element 30, the arch height HI shown in Fig. IB is minimized.

It will be appreciated that energy transmitted to first energy absorbing element 30 through application of a load to telescopic assembly 20, as explained hereinabove with respect to Figs. 1A, IB, 2A, 2B, 3A and 3B, is absorbed by energy absorbing element 30 through plastic deformation of first energy absorbing element 30. As explained previously, energy absorbing element 30 is configured to undergo plastic deformation when it is deformed from its initial shape, as shown in Figs. 1A and IB, to its compressed shape, as shown in Figs. 2A and 2B, when a compressive load is applied to telescopic assembly 20. Energy absorbing element 30 is also configured to undergo plastic deformation when it is deformed from its initial shape, as shown in Figs. 1A and IB, to its extended shape, as shown in Figs. 3A and 3B, when a tensile load is applied to telescopic assembly 20. However, it will be further appreciated that in accordance with the presently disclosed subject matter, an energy absorbing element 30 which has undergone deformation and become partially compressed or partially extended, can undergo additional deformation to become more or less compressed, more or less extended, compressed after having been previously extended, or extended after having been previously compressed. The energy absorbing element 30 which has undergone plastic deformation while being compressed to the maximal extent, will not be able to undergo additional plastic deformation so as to be compressed further, but will be able to undergo additional plastic deformation while being extended from the maximally compressed position. On the other hand, the energy absorbing element 30 which has undergone plastic deformation while being extended to the maximal extent, will not be able to undergo additional plastic deformation so as to be extended further, but will be able to undergo additional plastic deformation while being compressed from the maximally extended position.

For an energy absorbing element 30 shaped in accordance with the presently disclosed subject matter, for a given constant load, maximum displacement, as explained hereinabove with respect to Figs. 1B, 2B and 3B, allows maximum energy absorption. Since energy absorbing element 30 allows energy absorption under both compressive and tensile loads, the shape of energy absorbing element 30 can be tailored in accordance with design needs to have a greater allowance for tensile loads (i.e., allowable tensile displacement) at the expense of its allowance for compressive loads (i.e., allowable compressive displacement) and vice versa.

With respect to Figs. 1A, 1B, 2A and 2B, compressive displacement can be explained to be the total distance travelled by first end 32 and second end 34 from their initial locations in the initial shape of energy absorbing element 30 shown in Figs. 1A and 1B, to their locations in the compressed shape of energy absorbing element 30 shown in Figs. 2A and 2B, in other words, AD _I2 .

With respect to Figs. 1A, 1B, 3A and 3B, tensile displacement can be explained to be the total distance travelled by first end 32 and second end 34 from their initial locations in the initial shape of energy absorbing element 30 shown in Figs. 1A and 1B, to their locations in the extended shape of energy absorbing element 30 shown in Figs. 3 A and 3B, in other words, AD _I3 . In order to maximize energy absorption by maximizing allowable displacement, energy absorbing element 30 is composed of a ductile material having high elongation to break. Use of a ductile material having high elongation to break for energy absorbing element 30 allows energy to be absorbed by element 30 through plastic deformation of element 30. The amount of energy absorbed is high due to the very high plastic strain developed in energy absorbing element 30 when it is loaded. Furthermore, the range in which the energy absorbing element 30 works has a high margin of safety, so there is no risk of crack initiation.

The high elongation to break of the tensile material of which energy absorbing element is composed allows energy absorbing element 30 to undergo multiple cycles of compression and extension without breaking.

Returning now to the embodiment of energy absorbing element 30 shown in Fig. 1B, additional aspects of the shape of energy absorbing element 30 designed in accordance with the presently disclosed subject matter, will be discussed.

As shown in Fig. 1B, energy absorbing element 30 has a first leg 52 with said first end 32, a second leg 54 with said second end 34, and a bridging portion 58 interconnecting the first leg 52 and the second leg 54 and forming together a curved shape. The bridging portion 58, along with first leg 52 and second leg 54 form a continuous solid body. The initial shape of energy absorbing element 30 is a boomerang-like and symmetrical shape.

As further shown in Fig. 1B, an exemplary initial shape of energy absorbing element 30 has an outer surface 50 facing away from imaginary line L having lesser curvature than the inner surface 40. This can be seen in Fig. 1B where the radius rcso of the circle C50 on which outer surface 50 lies is larger than the radius rc40 of the circle C40 on which inner surface 40 lies, since a circle with a larger radius is less curved than a circle with a smaller radius.

As shown in Fig. 1B, energy absorbing element 30 further has a main axis M extending between the first end 32 and the second end 34, and cross-sections taken perpendicularly to said main axis have varying cross-sectional areas. This can be seen in Figs. 1C, 1D and 1E, which show exemplary cross-sections C-C, D-D, and E-E, respectively, taken at the farthest point PF, at an approximately central point along first leg 52, and at a location close to first end 32, respectively, along main axis M of energy absorbing element 30 as indicated in Fig. 1B. As further shown in Figs. 1B, 1C, 1D and 1E, an exemplary initial shape of energy absorbing element 30 has cross-sections along its main axis M wherein each of said cross-sections has a cross-sectional height taken on an imaginary plane including the imaginary line L shown in Fig. 1B, and a cross-sectional width extending along a plane perpendicular to the imaginary plane and in which the cross-section lies, and wherein the cross-sectional width in all the cross-sections is constant, and the cross- sectional height is varying.

It can further be understood from Figs. 1B, 1C, 1D and 1E, that the cross- sectional height of the cross-section including the farthest point PF, in an exemplary initial shape of energy absorbing element 30, is maximal with respect to the cross- sectional heights of the rest of the cross-sections along the main axis. This can be seen, as explained previously, in Figs. 1C, 1D and 1E where respective heights Flc, Ffo and Hi: of cross-sections C-C, D-D, and E-E, decrease in height with increasing distance from farthest point PF, from the maximal height Flc at the farthest point PF.

As further shown in Figs. 1B, 1C, 1D and 1E, the cross-sections along main axis M of an exemplary initial shape of energy absorbing element 30 are rectangular in shape. It will be appreciated that the shape of the cross-sections along main axis M of the initial shape of energy absorbing element 30 in accordance with the presently disclosed subject matter can be any shape, including a substantially rectangular or elliptical shape.

As can be seen in Figs. 1C, 1D and 1E, the cross-sectional width w is identical for all three cross-sections, while the cross-sectional heights Flc, FID and FIE vary, so that Flc > FID > FIE- Accordingly, the cross-sectional areas of the three cross-sections vary as well. The cross-sectional area of energy absorbing element 30 is maximal at farthest point PF. This can be seen in Figs. 1C, 1D and 1E, where the respective cross-sectional heights Flc, FID and FIE of cross-sections C-C, D-D, and E-E, taken at the farthest point PF, at an approximately central point along first leg 52, and at a location close to first end 32, respectively, along main axis M of energy absorbing element 30 as indicated in Fig. 1B, decrease in height with increasing distance from farthest point PF, from the maximal height Flc at the farthest point PF, to the minimal height FIE at a location close to first end 32.

It will be appreciated that the variation in the area of the cross-sections along main axis M in accordance with the presently disclosed subject matter, allows substantially uniform stress and strain to develop throughout energy absorbing element 30 when the compressive load or the tensile load is applied. Energy absorbing element 30 is designed to be thicker where axial loads on load limiter 10 can be expected to cause maximal bending moment and maximal stress, i.e. at the farthest point PF, and the stress is consequently distributed substantially uniformly throughout the element when load limiter 10 is loaded. This results in the energy absorbing element having a substantially uniform plastic deformation along its length when the load is applied, as opposed to the formation of a plastic hinge (which does not occur in the presently disclosed subject matter). Such a plastic hinge is formed when stress becomes concentrated in one location of a loaded element, and as a result extreme deformation occurs at that spot, resulting in a hinge effect, while the other parts of the element do not participate in the task of energy absorption, undergo little or no stress, and little or no deformation. Whereas the plastic deformation occurring in the area of a plastic hinge is inefficient, as it is a large amount of stress and strain occurring over a small area, the plastic deformation which occurs over energy absorbing element 30, is equivalent to the summation of small amounts of plastic deformation occurring over the entire element, and thus is highly efficient. The plastic deformation undergone by the element is maximal, i.e. the displacement undergone by the element is maximal, i.e. energy absorption is maximized for this shape.

It will further be appreciated that the formation of a plastic hinge in a structural element such as energy absorbing element 30, can be dangerous in a situation where safety is dependent upon the integrity of the structural element, since the formation of a plastic hinge at a particular location in the element is an indication that structural failure is occurring at the location of the plastic hinge, and that breakage of the element at that location is very likely to be imminent if the element continues to be loaded.

It will further be appreciated that, in accordance with the presently disclosed subject matter, an area of each of the cross-sections along the main axis M of energy absorbing element 30 is configured to vary in accordance with a calculated allowable bending moment for the energy absorbing element under design load at each of the cross-sections, such that the cross-sectional area is maximal at a location along the main axis M where the bending moment is maximal, and such that the cross-sectional area decreases in size along the main axis M proportionately in accordance with a reduction in values of the bending moment along the main axis M. It will further be appreciated that, in accordance with the presently disclosed subject matter, the variation of the cross-sectional areas along the main axis M is configured to allow a substantially uniform stress to develop along the energy absorbing element 30, when the load is applied.

It will still further be appreciated that, in accordance with the presently disclosed subject matter, the variation of the cross-sectional areas along the main axis M is configured to allow a substantially uniform strain to develop along the energy absorbing element, when the load is applied.

It can further be understood from Fig. 1B, that in accordance with the presently disclosed subject matter, the cross-sectional area at the farthest point PF is greater than the cross-sectional area at each of the first end 32 and the second end 34. As the initial shape of exemplary energy absorbing element 30 shown in Fig. 1B is symmetrical, as explained previously, the cross-sectional area of cross-section F-F, shown in Fig. 1B to be taken at a location on second leg 54 close to second end 34, corresponding to the location of cross-section E-E taken on first leg 52, is equivalent to the cross-sectional area of cross-section E-E.

It will further be appreciated that in addition to being as opposed to a plastic hinge, the energy absorbing element 30 is further configured to undergo permanent deformation of at least 0.2% at beginning of the deformation. For instance, the energy absorbing element 30 undergoes at least 0.2% permanent deformation even at the beginning of the deformation (upon application of load), as opposed to elastic springs. Such elastic springs are meant to deform elastically, at least until a respective elastic limit is reached thereby exhibiting zero plastic deformation at least until such elastic limit is reached.

It will be appreciated that the structural configuration of the energy absorbing element 30, including variable cross-sectional area along the length of the energy absorbing element and the cross-sectional height Flc (in Fig. 1C) of the cross-section including the farthest point P _F being greater than a cross-sectional width W (in Fig. 1C) of the cross-section including the farthest point P _F , enables the plastic deformation throughout the length of the energy absorbing element 30. The resultant permanent deformation of at least 0.2% signifies that for even an initial stress applied to the energy absorbing element, there would be at least 0.2% permanent strain experienced in the energy absorbing element upon removal of said stress. It will be appreciated that due to the structural configuration of load limiter 10 in accordance with the presently disclosed subject matter, i.e., the telescopic nature of telescopic assembly 20, the shape of energy absorbing elements 30, their composition of a ductile material having high elongation to break, their solid monolithic structure, and their disposition externally to telescopic assembly 20, as well as the pivotal nature of the pivotal connections between the ends 32 and 34 of energy absorbing elements 30, and the members 22 and 24 (respectively) of telescopic assembly 20, the following desirable outcomes are achieved with respect to the energy absorbing operation of load limiter 10: the load path of the load applied to load limiter 10 acts in the axial direction only along telescopic assembly 10, such that telescopic assembly 10 is unharmed after an energy absorption operation (compressive or tensile) of load limiter 10. Thus, load limiter 10 remains in working order to absorb energy in subsequent strokes of load applied to it.

Upon application of a known load to load limiter 10 designed on the basis of design requirements (e.g., anticipated loads), to absorb a calculable amount of energy through a calculable displacement in tension and / or compression, load limiter 10 transmits only a calculable constant load, and prevents bending moments from being transmitted.

In their disposition external to telescopic assembly 20, energy absorbing elements 30 are easily accessible for replacement when necessary.

The energy absorbing element 30 undergoes permanent deformation of at least 0.2% at beginning of deformation.

The plastic deformation of the energy absorbing element allows achieving maximum allowable plastic strain along its entire length up to the end of the deformation process.

According to a particular example of the presently disclosed subject matter according to which, the load limiter is mounted to a secondary strut of an inverse tripod structure comprising one of four landing legs of a lunar spacecraft, and can have the following characteristics:

- the energy absorbing element 30 can be composed of Stainless Steel 301 Annealed having elongation to break of 40%; and

- the energy absorbing element 30 can have a maximal cross-sectional height of 8 mm and a constant cross-sectional width of 5 mm.