GOLF CLUB WITH A CUSHION MADE OF VISCOELASTIC MATERIAL

Abstract

A golf club (10) is configured to dissipate kinetic energy during the impact when striking the golf ball, thereby to reduce the quantum of kinetic energy transferred from the golf club (10) to the ball and reducing the distance that the ball travels. The reduction in ball travel encourages the player to use more concentric muscle action at the moment of impact and thus to have better control over the impact. The golf club (10) includes a shaft (18) and a head (14) and the head (14) comprises a support structure (22) that is connected to the shaft (18), and an impact absorbent structure (16) that defines a face (46) of the golf club (10). The impact absorbent structure (16) includes a cushion (48), disposed between the face (46) and the support structure (22) and the cushion (48) is made of a shear thickening material.

Description

FIELD OF THE INVENTION

This invention relates to improvements in accuracy while playing golf. In particular, the invention relates to golf clubs for improved short game accuracy.

BACKGROUND TO THE INVENTION

When playing golf, the player swings the golf club so that the face of the club head hits the golf ball and kinetic energy is transferred from the golf club to the ball—which then travels towards the green and after successive shots, towards the hole. The transfer of kinetic energy is thus from the player to the club's shaft, to the club face and finally to the ball.

Most golf clubs have been developed to maximise the transfer of energy from a golf club to the golf ball in an attempt to allow the golf ball to be driven as far as possible. This approach works well in the long game, where the objective is generally to drive the ball as far as possible towards the green, but in the short game, the distances that the ball needs to travel are more easily achieved and the accuracy of play becomes more important—accuracy in both direction and distance.

Face inserts of materials that differ from the rest of the putter have been used in putters, but these face inserts were configured to increase perimeter weighting of the putters, to provide a softer feel and sound for the putters, and/or to enhances grip between the putter face and the ball (which reduces skid and varies roll of the ball).

These putter inserts did not result in sufficient improvement in accuracy. In fact, alleged success of many of these inserts is largely attributed to psychosomatic effects (the “placebo effect”).

The present invention seeks to provide improved accuracy in the golf short game in both distance and direction.

SUMMARY OF THE INVENTION

According to the present invention there is provided a golf club that is configured to dissipate kinetic energy during the impact when striking the golf ball, thereby to reduce the quantum of kinetic energy transferred from the golf club to the ball and reducing the distance that the ball travels. The golf club includes a shaft and a head and the head comprises:

• • a support structure that is connected to the shaft; and
  • an impact absorbent structure that defines a face of the golf club, said impact absorbent structure including a cushion, disposed between the face and the support structure;
  • wherein said cushion is made of a viscoelastic material is shear thickening, and it may be dilitant and/or rheopectic.

The definitions of “shear thickening”, “dilitant” and “rheopectic” vary, and typically refer to the “viscosity” of fluids. The viscoelastic materials suitable for the present invention resemble solids more than fluids, and the term “stiffness” (meaning “resistance to strain”) is used herein, although it has the same meaning as “viscosity”, in the context. Further, in this specification, the term “shear thickening” refers to an increase in stiffness with an increase in shear loads, “dilitant” refers to a time independent increase in stiffness with an increase in shear loads, and “rheopecty” refers to a time dependant increase in stiffness. It is clear that a material can exhibit more than one of these characteristics at the same time.

The impact absorbent structure may include one or more hard layer, that is harder than the cushion and the hard layer may be disposed adjacent the face of the golf club. The term “hard” refers in this specification to a resistance to stain and can for the purposes of this specification also be equated to “stiff”.

The hard layer may form the face of the golf club or may be embedded in the cushion, spaced from the face of the golf club. The impact absorbent structure may include a softer, compressible face layer, forming the face of the golf club, with the hard layer disposed between the cushion and the face layer.

The support structure may define a recess in which the impact absorbent structure is receivable—e.g. the impact absorbent structure may be a “face insert”.

The kinetic energy may be dissipated by converting it to potential energy or heat that may be stored in the club head and/or by creating an alternative load path for the loads exerted by the golf club on the ball.

The dissipation of kinetic energy may be achieved by allowing the club face to be compressed upon contacting the ball, wherein the compression is dampened, followed by dampened rebound, preferably exaggerated dampened rebound of the club face to its original position relative to the rest of the club head.

The golf club may have a mechanical construction which allows for dampened compression and/or dampened rebound and the dampening may include dissipation of kinetic energy by heat generation.

The golf club may include one or more biometric telemetry sensors that are configured to monitor movement of the golf club.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings.

Each of FIGS. 1 to 8 is a diagrammatic sectional side view of the head of a golf club with a short length of the shaft, adjacent the club head, and each of these figures shows a club head and shaft of a different conceptual embodiment of a golf club in accordance with the present invention;

FIG. 9 shows a three-dimensional view of a preferred embodiment of a golf club head in accordance with the present invention;

FIG. 10 shows an exploded view of the golf club head of FIG. 9;

FIGS. 11 to 15 show sectional side views of the golf club head of FIG. 9, with different inserts;

FIG. 16 shows an exploded view of an insert for the golf club head of FIG. 9;

FIG. 17 shows a three-dimensional view of an insert for the golf club head of FIG. 9;

FIG. 18 shows a part-exploded view of an insert for the golf club head of FIG. 9;

FIG. 19 shows a schematic diagram of experimental apparatus; and

FIG. 20 shows results of experiments conducted on different golf club heads, using the apparatus of FIG. 19.

DETAILED DESCRIPTION OF INVENTION WITH REFERENCE TO THE DRAWINGS

During a golf swing, like in all other voluntary human movements, each muscle involved in the movement can act in a concentric manner or in an eccentric manner. When a golf club is accelerated, this is achieved predominantly through concentric muscle action and when the golf club is decelerated, this is achieved predominantly through eccentric muscle action.

In concentric muscle action, the muscle contracts while generating tensile force in the direction of contraction and thus in the direction of movement. In eccentric muscle action, the muscle elongates while under tension due to an opposing force being greater than the tensile force generated by the muscle. The muscle thus acts to decelerate movement or otherwise controls a load, rather than generating a force in the direction of movement.

Muscle fibres create tension through cross-bridging between thick myosin filaments and thin actin filaments through the repeated binding and releasing of myosin heads to binding sites on the actin filaments. In concentric muscle action, the tensile force that the muscle needs to exert is calculated in the central nervous system and is brought into effect through cross-bridging and contraction of the muscle, as described above. The extent of the force is thus relatively simply under control of the central nervous system. By contrast, in eccentric muscle action, the force the muscle exerts is a result of an external, elongating force on the muscle and the smaller tensile force generated in the muscle through myosin and actin cross-bridging. The central nervous system can control the extent of the tensile muscle force, but has no control over the external force and consequently has to reassess the external force repeatedly by momentarily disconnecting the myosin-actin bridge. The control exercised by the central nervous system over eccentric muscle action is thus more complicated and discontinuous or less smooth than in the case of concentric action.

As a result of the different manners in which muscles exert tension when acting concentrically and eccentrically and in particular, the ways in which the muscles are controlled in these circumstances, much better control is exercised over concentric muscle action than eccentric muscle action.

When these principles are applied to a golf swing, better control over the muscle action is exercised during acceleration of the golf club (when muscle action is predominantly concentric) than during deceleration (when muscle action is predominantly eccentric). Accordingly, in order to allow better control over the golf swing at the time of striking the ball and thus improve the accuracy of play, the golf club should preferably be accelerating at the time of striking. This occurs reasonably naturally during the long game, when a player is seeking to drive the ball as far as possible and thus does not try to decelerate the golf club. However, in the short game, in an attempt to prevent hitting the ball too hard, players tend to start deceleration of the golf club before impact and the result is that at the critical moment of impact, the club is controlled by eccentric muscle movement, rather than by concentric muscle movement.

The present invention seeks to shorten the distance that the ball is driven by the golf club, so that the player is compelled to strike the ball harder and is thus encouraged to keep accelerating the golf club up to the time of impact. In order to shorten the distance that the ball travels, the quantum of kinetic energy that is transferred from the golf club to the ball needs to be reduced and this is sought to be done by dissipating the kinetic energy. This approach of dissipating kinetic energy to prevent the ball from travelling far is a drastic departure from the approach followed in existing golf club development, which seeks to maximise the transfer of kinetic energy to the ball.

Referring to FIGS. 1 to 8 of the drawings, eight different conceptual embodiments of golf clubs are shown, each of which is an example of how part of the kinetic energy that would otherwise have been transferred to the golf ball, can be dissipated. Each golf club is indicated generally by reference numeral 10, and features that are common between the different embodiments are identified by the same reference numerals, followed by suffixes that refer to the embodiments (and to the figure numbers).

Referring to FIG. 1, the first conceptual embodiment of a golf club 10.1 includes a shaft 12.1 and head 14.1 that form a contiguous, unitary construction of a resilient dampening material, with a suitably rigid club face insert 16.1. The material of the shaft 12.1 and head 14.1 is resiliently compressible, so that the insert 16.1 can be compressed upon impact with the ball and can rebound, but both the compression and the rebound is dampened, to reduce the transfer of kinetic energy from the club head 14.1 and insert 16.1 to the ball.

Strictly speaking, it is not the insert 16.1 that is compressed, but the club head 14.1 that is compressed by movement of the insert 16.1, and vice versa for rebound of the club face. However, in order to avoid unnecessarily lengthy descriptions, reference is made in this description to compression of the club face or of the club face insert or of the club head, interchangeably—all referring to a compression in which the club face is displaced relative to the rest of the club head.

Referring to FIG. 2, the second conceptual embodiment of a golf club 10.2 includes a club head 14.2 of resiliently compressible material that can dampen compression and rebound of a club face insert 16.2, as in the case of the golf club 10.1, but the club head 14.2 is attached to a conventional shaft 18.2.

Referring to FIG. 3, the third conceptual embodiment of a golf club 10.3 also includes a club head 14.3 of resiliently compressible material as in the case of the golf club 10.1 and the material may dampen compression and rebound of a club face insert 16.3, but the dampening effect is primarily caused by inserts 20.3 of dampening material, embedded within the club head 14.3.

Referring to FIG. 4, the fourth conceptual embodiment of a golf club 10.4 includes a shaft 18.4, similar to that shown in FIG. 2 and the shaft is contiguous with a hard retaining cup or outer shell 22.4 that extends around the solid club head 14.4, apart from the front of the club head, where the shell is open. The club head includes a face insert 16.4. The material of the club head 14.4 is resiliently compressible to allow the club face 16.4 to be compressed and to rebound and the material also dampens the compression and rebound, to reduce the transfer of kinetic energy from the club head 14.4 and insert 16.4 to the ball. The club head 14.4 may be attached to the inside of the shell 22.4 so that compression and rebound occurs purely as a result of deformation of the club head or (if permissible), a degree of sliding may be allowed between the club head and the shell—especially in the vicinity of the club face.

Referring to FIG. 5, the fifth conceptual embodiment of a golf club 10.5 includes a shaft 18.5 that is contiguous with a club head jacket 24.5 that extends around the club head 14.5 in similar fashion to the shell shown in FIG. 4, but the jacket 24.5 is open at the club face and at the rear of the club. The club head 14.5 and face insert 16.4 are generally similar to those shown in FIG. 4, but the opening at the rear of the jacket 24.5 places less restriction on deformation of the club head 14.5 during compression and rebound of the club face insert 16.5. Similarly to the golf club shown in FIG. 4, the club head 14.5 may be attached to the inside of the jacket 24.5 so that compression and rebound occurs purely as a result of deformation of the club head or (if permissible), a degree of sliding may be allowed between the club head and the jacket—especially in the vicinity of the club face.

Referring to FIG. 6, the sixth conceptual embodiment of a golf club 10.6 includes a contiguous shaft 18.6 and shell 22.6, with a club head 14.6 held inside the shell, similar to those shown in FIG. 4, but the club head 14.6 does not extend to the rear inside of the shell 22.6. Instead, a spring 26.6 or other mechanism is provided that assists in allowing compression and rebound of the club face. Preferably, the mechanism is configured for dampening of the compression and rebound. Similarly to the golf club shown in FIG. 4, the club head 14.6 may be attached to the inside of the shell 22.6 so that compression and rebound occurs purely as a result of deformation of the club head, with the spring 26.6 affecting the compression and rebound, or (if permissible), a degree of sliding may be allowed between the club head and the shell.

Referring to FIG. 7, the seventh conceptual embodiment of a golf club 10.7 includes a shaft 18.7 and club head 28.7 that form a continuous, unitary construction. A resiliently compressible layer 30.7 is provided at the front of the club head and a generally rigid outer cup 32.7 is fitted over the front of the club head, around the compressible layer 30.7. The cup 32.7 defines the club face. The cup 32.7 can slide relative to the head 28.7 while compressing the layer 30.7 during compression of the club face and the resilience of the layer causes the cup to slide away from the head during rebound of the club face. The compressible layer 30.7 dampens the compression and rebound movements to reduce the transfer of kinetic energy to the ball.

Referring to FIG. 8, the eighth conceptual embodiment of a golf club 10.8 includes a shaft 34.8 that is contiguous with a club head 36.8 and both the shaft and the club head are made from a composite material, which is configured (e.g. by material selection and/or orientation) to allow dampened compression and rebound of the club face, to reduce the transfer of kinetic energy from the club head 36.8 to the ball.

Further, the golf club 10.8 includes a biometric telemetry system 38.8, embedded in the club head 36.8, although in other embodiments, the telemetry system may be installed temporarily, The telemetry system is 38.8 is configured to monitor the transfer of kinetic energy from the club 10.8 to the ball, directly or indirectly. The telemetry system may be enhanced further by external equipment which measures or receives data relating to the accuracy of play, in directional and/or distance, which can be correlated to the readings on the telemetry system 38.8.

Referring to FIGS. 9 to 18, a preferred, practical embodiment of a golf club in accordance with the present invention is shown in the form of a putter, with some variations. The reference numbers used in FIGS. 1 to 8 are also used in FIGS. 9 to 18, but without suffixes.

The golf club 10 is configured to dissipate kinetic energy during the impact when striking the golf ball, and includes a shaft 18 (although only a short lower part of the shaft is shown in the drawings) and a head 14. The head 14 includes a support structure in the form of an outer shell 22 that is typically cast of metal and that is connected to the shaft 18, as well as an impact absorbent structure in the form of a club face insert 16 that defines a face 46 of the golf club 10.

The outer shell 22 has a back cavity 40 and interchangeable weights 42 can be attached to the body at the heel and toe ends of the back cavity, to alter the golf club's weight and/or moment of inertia (MOI). The positioning of the weights at the heel and toe, rather than the middle of the back cavity 40 also improves the MOI of the golf club. A recess 44 is defined in the face of the shell 22 in which the face insert 16 is receivable and the face insert may be attached permanently in the recess, or may be removably attached—e.g. it may be held in place with a friction fit, clips, of the like—depending on what is permissibly according to rules governing the game of golf.

Referring to FIG. 11, the entire first embodiment of the face insert 16 comprises a cushion that extends from the face 46 to the shell 22 and the cushion is made of a viscoelastic material in which stiffness of the material increases with the rate (speed) of compression of the cushion, i.e. the cushion becomes more stiff, the harder a golf ball drives into it. Examples of suitable materials include E-A-R ISODAMP C-1000 Series materials (available from Aearo Specialty Composites) which exhibit suitable velocity-sensitive compression resistance, i.e. they seem soft when they are compressed slowly, but which seem stiff when compressed quickly. The high internal damping properties of these C-1000 Series materials also inhibit vibration and shock, within limited deformation, without “bottoming out” (i.e. without compressing to the extent that it loses its viscoelastic properties).

Materials other than the C-1000 series materials can be used for the cushion (48), but such materials must be non-linear (referring to their stress-strain characteristics), non-newtonian, shear thickening, dilitant and/or rheopectic.

Referring to FIG. 12, the second embodiment of the face insert 16 consists mostly of the cushion 48, but the cushion does not extend all the way to the face 46. Instead, a hard layer 50 is attached to the cushion and forms the face. The hard layer 50 distributes the impact from the golf ball more evenly over the cushion 48 and provides a face 46 that is hard enough to comply with to rules governing the game of golf, e.g. the “R&A” rules.

Referring to FIG. 13, the third embodiment of the face insert 16 differs from the embodiment shown in FIG. 12 only in that it includes an additional soft face layer of surface coating 52 to create a softer feel and/or dampening effect, when striking the golf ball.

Referring to FIG. 14, the fourth embodiment of the face insert 16 differs from the embodiment shown in FIG. 11 only in that two harder layers 50 are embedded in the cushion 48. The hard layers 50 serve the same purposes as in the embodiments shown in FIGS. 12 and 13 and the thin part of the cushion 48 that extends between the face 46 and the hard layers 50 serves the same purpose as the soft surface coating shown in FIG. 13.

Referring to FIG. 15, the fifth embodiment of the face insert 16 differs from the embodiment shown in FIG. 14 only in that the hard layers 50 are not completely embedded in the cushion 48, but extend to the top of the cushion and can be withdrawn from the cushion and can be replaced with other hard layers, with different characteristics (e.g. different weight, stiffness, etc.).

FIGS. 16 to 18 show how hard layers 50 can be inserted and withdrawn from the cushions 48 in the embodiment of the face insert shown in FIG. 15, or in a similar embodiment including a single removable hard layer 50, instead of two.

The golf clubs shown in FIGS. 9 to 18 may also be equipped with one or more biometric telemetry sensors such as accelerometers that are configured to monitor movement of the golf club, to monitor the transfer of kinetic energy from the club to the ball, directly or indirectly, and/or to monitor accuracy of play, in direction and/or distance—as described above with reference to FIG. 8. The biometric telemetry system may be installed on the club head permanently or temporarily.

The golf club 10 is configured to dissipate kinetic energy when striking the golf ball, thereby to reduce the quantum of kinetic energy transferred from the golf club to the ball and reducing the distance that the ball travels. The effect is that more muscular input and recruitment is required to hit the ball the same distance and the player is required to use muscles concentrically and more muscle to get the same force applied to the ball.

Referring to FIGS. 19 and 20, experiments were conducted to assess the ability of the golf club 10 of the present invention, to dissipate kinetic energy when striking a golf ball.

Referring to FIG. 19, the experimental procedure involved dropping a pre-selected variety of golf balls 54 (a wide range of ball varying from soft to hard, but each of which complied with R&A and USGA rules) from a stationary condition through a drop guide 65 onto the face of a golf club in the form of a putter. The drop guide 56 served to ensure straight vertical free fall of the ball 54 and comprised of a tube of low friction material (to minimise spin of the ball) with an inside diameter of 42.67 mm. The drop guide 56 was positioned to ensure that the ball 54 would impact the face of the putter in the centre of the putter head sweet spot.

The putter was fixedly mounted in a putter mount 58, which was fixed to a load cell 60, which was fixedly onto a monolithic concrete base 62. No part of the base 62, load cell 60 or putter mount 58 had a resonant frequency which could affect the experimental results. The Load cell 60 was a HBM CFT 120 load cell and included an output recording and conditioning system and a measuring system with a frequency response in accordance with channel frequency class (CFC) 1000 of ISO 6487: 1987.

A vertical graduated pole 64 was provided adjacent the apparatus described above and a high speed camera was used to record images of the golf balls, during the experiments—to assist in accurate height measurements.

Setting up the equipment for each experiment included:

• • adjusting the drop guide 56 to the desired heights from which the ball 54 was required to be dropped. Experiments were conducted from drop heights of 200 cm, 150 cm and 100 cm above the putter face.
  • rigidly fixing the putter to be tested, in the putter mount 58 by screwing or clamping it in such a way that resonance will not affect the experimental results.
  • ensuring that the golf ball 54 impacts the sweet spot of the putter head.

The experimental tests included dropping each of the golf balls 54 through the drop guide 56 onto each of the putters and measuring the height by which the ball rebounded off the putter face—taken from the face of the putter to the lowest edge of the ball, with the aid of the high speed camera. Each experiment was repeated several times to ensure that consistent results were obtained. The force transmitted onto the load cell 60 was also measured for each experiment.

The putters that were used in the experiments were:

• • “Standard”: Three standard putters were used and the averages were taken for the experimental results for these three putters. The three putters were Odyssey [white hot xg], Wilson [P Steff lady—soft feel], and a putter as shown in FIGS. 9 and 10 of the present application, with a solid stainless steel face insert;
  • “Straight Aim”: a putter with a face insert intended to assist in putting distance control:
  • “Leatt R&A”: a putter as described above, with reference to FIG. 12, using C-1002 material in its cushion 48 and a hard layer 50 of hard wood with a thickness of about 2 mm (although experimental results did not differ appreciably when layers 50 of steel, aluminium or hard plastic materials); and
  • “Leatt Max”: a putter as described above, with reference to FIG. 11, using C-1002 material in its cushion (48).

Referring to FIG. 20, experimental results are shown for the maximum rebound heights achieved in drop tests from drop heights of 200 cm, 150 cm and 100 cm, for Standard and Leatt Max putters.

Additional test results including maximum rebound heights (in centimetres) and load cell force (in Newton) for all four putters and all three drop heights are provided in the table below (amounts shown in brackets are percentage reductions, when compared to “Standard” putters):

			100 cm
	200 cm drop height	150 cm drop height	drop height
	rebound	force	rebound	force	rebound	force
Standard	139	982	103	860	76	713
Straight	122 (12%)	820 (16%)	96 (7%)	820 (5%)	67	650
Aim					(12%)	(9%)
Leatt	72 (48%)	880 (10%)	44 (57%)	670 (22%)	35	590
R&A					(53%)	(17%)
Leatt	45 (68%)	770 (22%)	35 (66%)	630 (27%)	20	490
Max					(74%)	(31%)

The experimental results show that, while there is a slight reduction in rebound height from Standard putters to Straight Aim putters, this is very little compared to the very drastic reduction in rebound height when using the Leatt R&A and the Leatt Max putters of the present invention. The reduction in rebound height is conclusive proof that the putters of the present invention are extremely effective in dissipating kinetic energy during the impact when striking the golf ball, reducing the kinetic energy transferred to the ball and reducing the distance that the ball travels—with the resulting use of concentric muscle action at the moment of impact and improved control, as described above.

There is al so a reduction in maximum force transmitted to the load cell 60—which confirms the dissipation of kinetic energy.

Claims

1-7. (canceled)

8. A golf club including a shaft and a head, said head comprising:

a support structure that is connected to the shaft; and

an impact absorbent structure that defines a face of the golf club, said impact absorbent structure including a cushion, disposed between the face and the support structure; wherein said cushion is made of a viscoelastic material that is rheopectic.

9. A golf club according to claim 8, wherein said impact absorbent structure includes at least one hard layer, that is harder than the cushion, said hard layer being disposed adjacent the face of the golf club.

10. A golf club according to claim 8, wherein said hard layer forms the face of the golf club.

11. A golf club according to claim 8, wherein said hard layer is embedded in the cushion and is spaced from the face of the golf club.

12. A golf club according to claim 11, the impact absorbent structure includes a softer, compressible face layer, forming the face of the golf club, with said hard layer disposed between the cushion and said face layer.

13. A golf club according to claim 8, wherein said support structure defines a recess in which said impact absorbent structure is receivable.

14. A golf club according to claim 8, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

15. A golf club according to claim 9, wherein said hard layer forms the face of the golf club.

16. A golf club according to claim 9, wherein said hard layer is embedded in the cushion and is spaced from the face of the golf club.

17. A golf club according to claim 9, wherein said support structure defines a recess in which said impact absorbent structure is receivable.

18. A golf club according to claim 10, wherein said support structure defines a recess in which said impact absorbent structure is receivable.

19. A golf club according to claim 11, wherein said support structure defines a recess in which said impact absorbent structure is receivable.

20. A golf club according to claim 12, wherein said support structure defines a recess in which said impact absorbent structure is receivable.

21. A golf club according to claim 9, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

22. A golf club according to claim 10, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

23. A golf club according to claim 11, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

24. A golf club according to claim 12, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

25. A golf club according to claim 13, wherein said golf club includes at least one biometric telemetry sensor that is configured to monitor movement of the golf club.

26. A golf club according to claim 16, the impact absorbent structure includes a softer, compressible face layer, forming the face of the golf club, with said hard layer disposed between the cushion and said face layer.

27. A golf club according to claim 15, wherein said support structure defines a recess in which said impact absorbent structure is receivable.