Improvements In or Relating To Vehicle Bumpers

The present invention, relates to vehicle bumpers or fenders and particularly to the front bumper arrangement of a road vehicle.

It is envisaged that legislative requirements will require vehicle front bumpers to exhibit differing magnitudes of resistive force during deflection thereof in various collision situations. More specifically, it is envisaged that differing magnitudes of resistive force will be required to ensure vehicle preservation during low speed parking impacts, pedestrian safety in the event of the vehicle striking a pedestrian, and occupant safety in the event of the vehicle colliding with, for example, a stationary vehicle.

It is highly desirable to provide a vehicle with a front bumper arrangement having a variable resistance to forces applied thereto, said arrangement being coupled to an appropriately configured sensor and activation package which monitors both vehicle operating parameters and the nature and orientation of objects with, which a collision may occur, In the event that a collision with an object is deemed imminent, the package is able to rapidly assess operative parameters of the vehicle such as, for example, steering input and acceleration/deceleration, as well as parameters of the object such as, for example, size, mass, direction of travel, and in the event that the object is a pedestrian, the likelihood of injury, and configure the resistance of the bumper arrangement accordingly. Known object recognition systems which may be incorporated in to such an overall system may operate on a visual basis. Alternatively, or in addition to such a visual system, the recognition system may be operable to monitor signals broadcast by an object.

The overall aim of such a system is to provide a vehicle with means to accurately asses the nature of a collision object and, by configuring the bumper arrangement accordingly, minimise damage to the object and vehicle, while maintaining occupant safety _* A vehicle thus equipped may therefore be able to differentiate between, for example, stationary and moving vehicles, pedestrians, cyclists, wildlife and items of

road and street furniture. In the case of pedestrians, the system may be further configured to take into account such factors as the size, mass and orientation relative to the vehicle of the pedestrian, and assess via an understanding of the kinematics of a human body when struck and the shape and configuration of the vehicle, the likelihood of injury. Taking the example of a front bumper impact upon a human legform, it is acknowledged that keeping the acceleration applied thereto below 150g will typically not result in bone breakage.

It is therefore an aim of the present invention to provide a vehicle bumper arrangement incorporating a force absorption device, and a method of operating such an arrangement, which seeks to minimise the maximum acceleration experienced by an object struck by the bumper arrangement while being able to be accommodated within the available space envelope for such an arrangement on a vehicle.

According to a first aspect of the present invention there is provided a vehicle bumper arrangement comprising a bumper element and a force absorption device positioned between the bumper element and a structure of the vehicle, the bumper element being movable in the direction of the structure of the vehicle in response to an external force applied thereto, the force absorption device being configurable to provide a differing magnitude of resistive force to the applied external force.

The present invention provides a vehicle bumper arrangement which is operable to provide a selected resistive force which is substantially constant and independent of the speed of movement or deformation of the bumper element.

In a first embodiment of the present invention, the force absorption device may be configured so as to be able to provide multiple discrete values of resistive force, one of which values is selected prior to, or shortly after, movement of the bumper element in the direction of the vehicle structure. In an alternative second embodiment, the force absorption device may be configured so as to be able to provide an infinitely variable range of resistive force magnitudes between defined upper and lower limits, one of

which magnitudes is selected prior to, or shortly after, movement of the bumper element in the direction of the vehicle structure.

With regard to said first embodiment, the force absorption device may comprise a hydraulic cylinder mounted to the vehicle and having a piston movable within the bore of said cylinder by the bumper element. The cylinder is provided with a relief valve operable to permit fluid within the cylinder to vent to a reservoir when a predetermined pressure within the cylinder is exceeded and thereby maintain a constant resistive force to movement of the piston by the bumper element, said relief valve being configurable so as to provide a range of relief pressures. The relief valve may be provided with a pilot valve operable to vent fluid from the cylinder in the event that the predetermined relief pressure is only slightly exceeded.

Alternatively, the force absorption device may comprise a hydraulic cylinder mounted to the vehicle and having at least two pistons which are selectively movable within the bore of said cylinder by the bumper element, each of said pistons being configured so as to provide differing resistance to movement within the cylinder. The device may be provided with a rod connected to the bumper element and extending into the hydraulic cylinder, and a coupling arrangement to $electively couple one or bolh of said pistons to said rod.

The coupling arrangement may comprise a deployable arrangement of the rod. The arrangement may be operable to couple a single piston to the rod, or both pistons to the rod. Where both pistons are coupled to the rod, this may be achieved by coupling a first piston to the rod and then moving the second piston by contact with said first piston In such an embodiment, the coupling arrangement may comprise projections or fingers of the rod which are selectively movable into and out of engagement with a piston. Alternatively, the coupling arrangement may comprise a plurality of balls or rollers provided between opposed ramped surfaces of the rod and at least one of the pistons. In use, movement of the rod causes the rollers to move over the ramped surface of the rod and into contact with the ramped surfaces of the piston, thereby coupling the piston to the rod.

The coupling arrangement may alternatively comprise a gripping arrangement which is mounted to one of the rod and a piston and operable to grip the other of the rod and said piston. The gripping arrangement is operable to provide a fiictional connection between the piston and rod. In a preferred embodiment, the coupling arrangement includes a tubular sleeve mounted to the piston, which sleeve is configured so as to be able to contract and grip the piston. The piston may be provided with an annular skirt which is grippable by the sleeve. The sleeve may be formed form a material which is configured so as to contract when a tensile load is applies there to. The sleeve may be formed from a woven mesh of, for example, carbon fibre, Keviar or stainless steel filaments.

In an alternative embodiment, the force absorption device may comprise plurality of deformable elements mounted to the vehicle and a reconfigurable interface member movable by the bumper element into contact with none, some or all of the deformable elements. The deformable elements may comprise projections or columns which, are configured so as to bendable or crushabie between the interface member and the vehicle structure. The elements may each have a differing yield strength. Alternatively, the elements may have substantially equal yield strengths. The interface member is configurable to contact predetermined combinations of said columns so as to provide a predetermined resistive force to the movement of the bumper element. The interface member may be provided with a combination of through apertures, within which a deformable element can be received, and abutment faces, against which a deforraable element can be contacted. By selectively aligning the apertures and abutment faces with the deformable elements, a desired resistive force can be selected. In a preferred embodiment, the interface member may take the form of a disc having an axis of rotation, with the deformable elements arranged around said axis.

hi yet a further embodiment of the present invention the force absorption device may comprise a body having a variable aperture mounted to the vehicle and a member movable through said aperture by the bumper element, the aperture of the body being variable so as to produce a differing interference fit between the body and the member.

By varying the fit in this manner the factional interaction between the member and body can be changed and thus the resistive force to movement of the bumper element altered. Ih one embodiment the body may be comprised of a magneto-strictive material and surrounded by a coil operable to produce a magnetic field in the vicinity of the body. In an alternative embodiment, the body many be comprised of an electro-strictive material and surrounded by means operable to produce an electric field in the vicinity of the body.

In a further embodiment, the force absorption device may comprise a hydraulic cylinder mounted to the vehicle and having a piston movable within the bore of said cylinder by the bumper element, the cylinder containing a magneto-rheological fluid and means to produce a magnetic field to alter the viscosity of fluid flowing through or around the piston and thereby alter the resistance to movement of the piston within the cylinder.

In one embodiment the piston may be provided with a through aperture surrounded by a coil, said coil being energisable so as to alter the viscosity of fluid flowing through the aperture. In an alternative embodiment, the cylinder may be provided with a bypass duct arranged so as to permit fluid to flow within the cylinder from one side of the piston to the other, the duct including a coil eriergisable so as to alter the viscosity of fluid flowing through the duct. In yet a further embodiment, the diameter of the piston may be less than the internal bore of the cylinder such that an annular passage is defined between the piston and cylinder, wherein means are provided to produce a magnetic field in the vicinity of the annular passage to alter the viscosity of fluid flowing therethrough.

In yet. another embodiment of the present invention the force absorption device may comprise a hydraulic cylinder mounted to the vehicle and having a piston movable within the bore of said cylinder by the bumper element, wherein the piston is tapered and movable through a variably sized orifice of the cylinder. In such an embodiment the piston may be provided with an exponential taper. The size of the orifice may be varied by the introduction of differently dimensioned annular inserts into the orifice.

According to a second aspect of the present invention there is provided a vehicle bumper force absorption device mouotable between a vehicle structure and a bumper element, the force absorption device comprising a hydraulic cylinder having a piston movable within the bore of said cylinder by the bumper element, and a relief valve operable to permit fluid within the cylinder to vent to a reservoir when a predetermined pressure within file cylinder is exceeded and thereby maintain a constant resistive force to movement of the piston by the bumper element, said relief valve being configurable so as to provide a range of relief pressures. The relief valve may be provided with a pilot valve operable to vent fluid from the cylinder in the event that the predetermined relief pressure is only slightly exceeded.

According to a third aspect of the present invention there is provided a vehicle bumper force absorption device mountable between a vehicle structure and a bumper element, the force absorption device comprising a hydraulic cylinder having at least two pistons which are selectively movable within the bore of said cylinder by the bumper element _^ each of said pistons being configured so as to provide differing resistance to movement within the cylinder. The device may be provided with a rod connected to a bumper element and extending into the hydraulic cylinder, and a coupling arrangement to selectively couple one or both of said pistons to said rod.

The coupling arrangement may comprise a deployable arrangement of the rod. The arrangement may be operable to couple a single piston to the rod, or both pistons to the rod. Where both pistons are coupled to the rod, this may be achieved by coupling a first piston to the rod and then moving the second piston by contact with said first piston In such an embodiment, the coupling arrangement may comprise projections or fingers of the rod which are selectively movable into and out of engagement with a piston. Alternatively, the coupling arrangement may comprise a plurality of balls or rollers provided between opposed ramped surfaces of the rod and at least one of the pistons. In use, movement of the rod causes the rollers to move over the ramped surface of the rod and into contact with the ramped surfaces of the piston, thereby coupling the piston to the rod.

The coupling arrangement may alternatively comprise a gripping arrangement which is mounted to one of the rod and a piston and operable to grip the other of the rod and said piston. The gripping arrangement is operable to provide a frictional connection between the piston and rod. In a preferred embodiment, the coupling arrangement includes a tubular sleeve mounted to the piston, which sleeve is configured so as to be able to contract and grip the piston. The piston may be provided with an annular skirt which is grippable by the sleeve. The sleeve may be formed form a material which is configured so as to contract when a tensile load is applies there to. The sleeve may be formed from a woven mesh of, for example, carbon fibre, Kevlar or stainless steel filaments.

According to a fourth aspect of the present invention there is provided a vehicle bumper force absorption device mountahle between a vehicle structure and a bumper element, the force absorption device comprising plurality of deformable elements mountable to the vehicle and a recoπfigurable interface member movable by the bumper element into contact with none, some or all of the deformable elements. The deformable elements may comprise projections or columns which are configured so as to bendable or crushable between the interface member and the vehicle structure. The elements may each have a differing yield strength. Alternatively, the elements may have substantially equal yield strengths. The interface member is configurable to contact predetermined combinations of said columns so as to provide a predetermined resistive force to the movement of the bumper element. The interface member may be provided with a combination of through apertures, within which a deformable element can be received, and abutment faces, against which a deformable element can be contacted. By selectively aligning the apertures and abutment faces with the deformable elements, a desired resistive force can be selected. In a preferred embodiment, the interface member may take the form of a disc having an axis of rotation, with the deformable elements arranged around said axis.

According to a fifth aspect of the present invention mere is provided a vehicle bumper force absorption device mountable between a vehicle structure and a bumper element,

the force absorption device comprising a body having a variable aperture mountable to the vehicle and a member movable through said aperture by the bumper element, the aperture of the body being variable so as to produce a differing interference fit between the body and the member. By varying the fit in this manner the Motional interaction between the member and body can be changed and thus the resistive force to movement of the bumper element altered. In one embodiment the body may be comprised of a magneto-strictive material and surrounded by a coil operable to produce a magnetic field in the vicinity of the body. In an alternative embodiment, the body many be comprised of an electro-strictive material and surrounded by means operable to produce an electric field in the vicinity of the body.

According to a sixth aspect of the present invention there is provided a vehicle bumper force absorption device mountable between a vehicle structure and a bumper element, the force absorption device comprising a hydraulic cylinder mountable to the vehicle and having a piston movable within the bore of said cylinder by the bumper element, the cylinder containing a magneto-rheological fluid and means to produce a magnetic field to alter the viscosity of fluid flowing through or around the piston and thereby alter the resistance to movement of the piston within the cylinder.

In one embodiment the piston may be provided with a through aperture surrounded by a coil, said coil being energjsable so as to alter the viscosity of fluid flowing through the aperture. In an alternative embodiment, the cylinder may be provided with a bypass duct arranged so as to permit fluid to flow within the cylinder from one side of the piston to the other, the duct including a coil energisable so as to alter the viscosity of fluid flowing through the duct. Ih yet a further embodiment, the diameter of the piston may be less than the internal bore of the cylinder such that an annular passage is defined between the piston and cylinder, wherein means are provided to produce a magnetic field in the vicinity of the annular passage to alter the viscosity of fluid flowing therethrough.

According to a seventh aspect of the present invention there is provided a vehicle bumper force absorption device mountable between a vehicle structure and a bumper

element, the force absorption device comprising a hydraulic cylinder mountable to the vehicle and having a piston movable within the bore of said cylinder by the bumper element, wherein the piston is tapered and movable through a variably sized orifice of the cylinder. In such an embodiment the piston may be provided with an exponential taper. The size of the orifice may be varied by the introduction of differently dimensioned annular inserts into the orifice.

According to a further aspect of the present invention there is provided a method of varying the magnitude of resistive force applied to a bumper element of a vehicle, the method comprising the steps of: providing a vehicle having a bumper arrangement comprising a bumper element and a force absorption device positioned between the bumper element and a structure of the vehicle, the bumper element being movable in the direction of the structure of the vehicle in response to an external force applied thereto, the force absorption device being configurable to provide a differing magnitude of resistive force to the applied external force; providing the vehicle with means to determine that a collision event is going to occur and to estimate the nature of said collision event; and configuring the force absorption device to provide a resistive force related to said estimated nature of the collision event in advance of said collision event occurring.

In a preferred embodiment, the method includes the additional step of monitoring said collision event and, if deemed necessary, reconfiguring the force absorption device to provide a differing resistive force during said collision event.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a simplified plan view of a road vehicle bumper arrangement Figure 2 shows a simplified sectional view of a bumper hydraulic force absorption device having a pressure relief valve;

Figures 3 to 5 show cross-sectional views of a pressure relief valve;

Figure 6 shows a cross-sectional view of a bumper force absorption device incorporating a constant force spring;

Figures 7 to 9 show cross-sectional views of bumper force absorption devices incorporating magneto-rheological or electro-rheological fluid; Figure 10a shows a cross-sectional view of a bumper force absorption device having a controllable interference fit;

Figure 10b shows an end view of the device of figure I Oa

Figure 11 shows a cross-sectional view of a bumper force absorption device containing selectable defoπnable elements Figure 12 shows an end view of a selection rotor of the device of figure 11 ;

Figure 13 show a cross-sectional view of a bumper force absorption device having selectively couplable pistons;

Figures 14 and 15 show schematic representations of piston coupling arrangements;

Figures 16 to 18 show more detailed cross-sectional views of a bumper force absorption device having selectively couplable pistons;

Figures 19 and 20 show cross-sectional views of an alternative embodiment of a bumper fbree absorption device having selectively couplable pistons; and

Figures 21 to 23 show cross sectional views of a bumper force absorption device having a tapered piston.

Referring firstly to figure 1 there is shown a schematic plan view of a vehicle bumper arrangement generally designated 10. The arrangement 10 comprises a bumper beam 12 which is mounted to a structure 14 of the vehicle, for example longitudinally extending crash members of the vehicle chassis, by force absorption devices 16. In the embodiment shown, each device 16 includes a rod 18 which is movable into the body 20 of the device 16 as a result of the beam 12 being moved towards the vehicle structure 14. It will thus be understood that an impact load 22 applied to the beam 12 is transferred to the vehicle structure 14 by the absorption devices 16. To minimise the possibility of injury to both a pedestrian struck by the beam 12, and the occupants of the vehicle in instances where a collision occurs with another vehicle or similar large object, it is desirable that the force absorption devices 16 generate substantially constant resistive forces which are independent of the speed of movement of the beam 12 in the

direction of the vehicle structure. The absorption devices 16 may be positioned within hollow elements 15 of the vehicle structure 14 so as to efficiently use the available space on the vehicle. Ih the event of a significant impact the beam 12 may be moved into contact with the hollow elements 15 which themselves may crumple or otherwise deform to absorb the energy of the impact.

The arrangement 10 is shown to have two devices 16, however it will be understood that that the arrangement may alternatively have only one device 16 or more than two devices.

Figure 2 shows a simplified cross-sectional view of a force absorption device 16 in the form of a hydraulic cylinder. The device 16 includes a cylinder 24 containing a hydraulic fluid, and a piston 26 connected to the rod 18. The piston 26 is provided with optional through apertures 28 which permit hydraulic fluid to pass from one side of the piston 26 to the other as a result of movent of the piston 26 within the bore of the cylinder 24, The flow of fluid through the apertures 28 produces a force which resists the movement of the piston 26 through the cylinder 24 The device 16 is further provided with a pressure relief valve generally designated 30 which is operable to permit hydraulic fluid to pass from the cylinder 24 to a reservoir 32 when predetermined pressure conditions within the cylinder are experienced.

Figures 3 to 5 show a pressure relief valve 30 of the type suitable for use with the device 16 of figure 2. The valve includes a casing 36 defining a cavity 37, and having pilot valve 38 and a relief valve 40. In use, fluid within the cavity 37 is pressurised by the piston 26 The pilot valve 38 includes a pilot valve member 41 and a seat 42. The valve member is connected via a rod 44 to an actuator 46 which is operable to vary the force required to open the pilot valve 30. The actuator 46 is sensitive to the pressure within the cylinder 24. A return spring 48 is provided to bias the valve member 41 towards the seat 42.

The relief valve 40 includes a relief valve member 50 and a seat 52. The seat 52 surrounds an outlet aperture 54 of the valve casing 36 which is in fluid communication

with the hydraulic fluid reservoir 32. The relief valve member 50 is hollow and is provided with a through bore 56. As will be described in greater detail below, the through bore 56 permits fluid which has passed through the pilot valve 38 to reach the reservoir 32. The relief valve 40 further includes a spring 58 which urges the relief valve member 50 in the direction of the valve seat 52. The relief valve member 50 is further provided with a skirt 60 which is received in a complementarily shaped recess 62 of the casing 36. The skirt 60 is provided with an aperture 64 which permits hydraulic fluid to pass from one side of the skirt to the other and into a passage 66 in the casing 36 which leads to the pilot valve 38.

In use, regulation or opening pressures are chosen for the pilot and relief valves 38,40. The actuator 46 permits the opening pressure of the pilot valve 38 to be varied. In the embodiment shown, the opening pressure of the relief valve 40 is governed by the strength of ihe spring 58. It will be understood that the relief valve 40 may also be provided with an actuator operable to vary the opening pressure. Figure 3 shows the situation where the pressure in the cavity 37 is less than the opening pressures of the valves 38,40. Figure 4 illustrates the situation where the pressure within the cavity 37 is greater that the opening pressure of the pilot valve 38 but less than the opening pressure of the relief valve 40. The pilot valve member 41 is moved from its seat 42 and fluid is thus able to flow into the passage 66, through the pilot valve 38, through the bore 56 of the relief valve member 50 and into the reservoir 32 through the valve outlet aperture 54. Figure 5 shows the configuration of the valve 30 where the pressure within the cavity 27 is greater than opening pressure of both the pilot and relief valves 38,40. The pressure applied to the skirt 60 of the relief valve member 50 lifts the valve member 50 from its seat 52 and permits fluid to flow to the reservoir 332 both around and through the valve member 50. It will be understood that by allowing fluid to flow to the reservoir through the pilot valve 38 or both the pilot and relief valves 38,40, the force resisting the movement of the piston 36 through the bore of the cylinder 24 is reduced,

Figure 6 shows an alternative embodiment of a force absorption device generally designated 116. Features common to the force absorption device described with

reference to the preceding figures are identified with like reference numerals. The device 116 utilises spring force to resist the movement of the rod 18 into the cylinder 24 under the influence of an applied force 68, and embodies a hydraulic damper arrangement to dissipate force stored in the springs as a result of movement of the rod 18. The rod 18 is provided with a fixed mount 70 to which are connected a pair of constant force springs 72. Each spring 72 is comprised of a thin, spiral wound strip of metal with inherent curvature which results in each turn of die strip wrapping tightly around its adjacent neighbour. When the strip is extended, the inherent stress within, the coils resists the loading force, just as in a common helical extension spring but with approximately constant force. In the embodiment shown, a free end 74 of each spring 72 is connected to the mount 70, while the body of each spring 72 is rigidly connected to a base member 76 for the device 116 which, in use, permits mounting of the device 116 to a vehicle structure. As will be readily appreciated, movement of the rod 1 S and mount 70 in the direction of the base member 76 causes extension of the springs 72 and hence a resistive force to be applied to the rod.

A clutch arrangement 78 is provided between the rod 18 and the piston 26 which permits the rod 18 to move relative to the piston 26 in the direction indicated by the applied force 68, but couples the rod IS to the piston 26 when the rod moves 18 in the opposite direction. The piston 26 thus does not resist movement of the rod 18 which results in the storage of energy in the springs 72, but instead acts to resist movement of the rod when said stored energy is released. In the embodiment shown, the clutch 78 comprises a plurality of ball or roller elements 80 which surround the rod 18 and are retained within a frusto-coniocal through aperture 82 of Hie piston. The clutch 78 is configured such that the roller elements 80 are urged into contact with the wall of the aperture 82 by movement of the rod 18 under the influence of the springs 72. The cylinder 24 is further provided with a clutch disengagement mechanism 84 at one end thereof comprising, for example, a plurality of fingers arranged to contact the roller elements 80. A coil spring 86 is provided within the cylinder 24 to move the piston 26 back to its initial position against a stop 88.

Figures 7 to 9 show three different embodiments of a force absorption device _s generally designated 216% 216" and 216"% "which are configured for use with a magneto-rheological fluid. As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals. In the embodiment of figure 7, the piston 26 is provided with circumferential seals 90 so as to ensure a fluid tight seal between the piston 26 and the bore of the cylinder 24. The cylinder 24 is grounded and piston apertures 28 are surrounded by electromagnetic coils 92 to which is connected an extensible power supply conduit 94. In use, the viscosity of the fluid passing through the apertures 28 can be varied by altering the magnetic field provided by the coils 92 in the vicinity of the apertures 2O ₃ and consequently the resistance of the piston 26 and rod 18 to the applied force 86 changed.

The device 216" of figure 8 a coil 92 is incorporated within the piston 26 and the piston 26 is sized such that an annular space 96 is defined between the piston 26 and the bore of the cylinder 24. The coil 92 is energisabie so as to provide a magnetic field in the vicinity of the annular space 92. As before, the viscosity of the fluid passing through the space 92 can be varied by altering the magnetic field provided by the coil 92, and consequently the resistance of the piston 26 and rod 18 to the applied force 86 changed. The device 216" of figure 7 dispenses with the seals 90 of the device 216' of figure 7, however the complexity of the extendible power conduit 94 remains.

The device 216*" of figure 9 utilises a bypass duct 98 to permit fluid to move across the piston 26 as the result of movement of the piston 26 within the bore of the cylinder 24. An electromagnetic coil 92 is provided around the duct 98 and is operable in the same manner as before to restrict the flow of fluid through the duct 98.

The devices 216', 216" and 216'" of figures 7 to 9 have been described with reference to the use of a magneto-rheological fluid. It will be understood, however, that with appropriate changes to provide a potential difference, rather than a magnetic field, then an electro-rheological fluid may be used.

Figure 10a shows a schematic view of a force absorption device generally designated 316 which operates on a magneto-strictive or electro-constrictive principle. As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals. The rod 18, which is connected to the bumper beam, passes through an aperture 100 provided in a grounded annular body 102 of a magneto-strictive material. The rod 18 runs through a flanged bush 101 which abuts a portion of the vehicle structure. The bush 101 may be manufactured ftorn, for example, non magnetic stainless steel. The bush 101 is provided so as to prevent damage to the magneto-strictive material as a result of movement of the rod 18. The bush 101, and potentially the rod 18 may be considered to be sacrificial in that they may need to be replaced after a collision when the device 316 is reset. The body 102 is surrounded by a coil 92 which is energisable so as to alter the shape of the body 102 and hence alter the characteristics of the aperture 100. The aperture 100 may accordingly be modified so as to provide a controllable interference fit between the rod 18 and the body 102.

hi an alternative embodiment, the device 316 may be provided with segments of magneto-strictive material 102 arranged around the bush 101 as indicated in figure 10b. The magneto-strictive material my comprise, for example, Terfenol D (rtm).

The magneto-restrictive material of the body 102 may be substituted for an electro-strictive material, with the coil 92 replaced by appropriate means for generating an electric field in the vicinity of the body 102.

Referring now to figures 11 and 12 there is shown a force absorption device generally designated 416 which incorporates selectable deformable elements. As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals. The device 416 includes a selection rotor 104 which is rotatably mounted to the rod 18, and a pair of deformable columns 106, 108 which are mounted to the vehicle structure. The columns 106, 108 may be manufactured from a bulk metal or a metal foam. The columns 106,108 may, for example, be comprised of a stabilised aluminium foam or an expanded aluminium

honeycomb material. The columns 106,108 each have different diameters such that each column 106,108 has a different yield strengths. For example, the smaller column 106 may have a yield strength of 60 kN, and the larger column 108 a yield strength of 9OkN, such that the columns 106, 108 in combination have a yield strength of 15OkN.

The selection rotor 104 is provided with three through apertures 110,112 comprising two larger diameter apertures 110 and one smaller diameter aperture 112. The apertures 110,112 are sized such that the columns 106,108 are receivable therethrough without impediment. The rotor 104 is rotatable between three positions relative to the columns 106,108. In the first position, indicated by broken line 114, both a large and small aperture 110,112 are aligned with the large 108 and small 106 column respectively. In use, movement of the rod 18 and rotor 104 in the direction of the columns 106,108 results in the columns 106,108 being received in the apertures 112,110 with the result that no resistance to the movement of the rod 18 is provided. In the second position of the rotor 104, indicated by broken line 118, a large aperture 110 is aligned with the larger column 108, while the smaller column 106 faces an engagement portion 120 of the rotor. In this position movement of the rod 18 and rotor 104 in the direction of (he columns 106,108 results in the larger column 108 being received in the aperture 110 and the smaller column 106 crushed by the rotor 104, with the result that a resistive force of 60 kN is applied to the movement of the rod 18 by the deformation of the column 106. In the third position, indicated by broken line 122, both columns 106,108 are faced by engagement portions 120 of the rotor 104 with the result that, in use, a resistive force of 150 kN is applied to the movement of the rod 18 by the deformation of both columns 106,108.

Rotation of the rotor 104 may be achieved by the provision of a geared electric motor acting upon a gear attached to the rotor 104. In an alternative embodiment, the grounding via, for example, a zero air gap electromagnet of one of the columns 106,108 may be utilised to rotate the rotor 104 either clockwise or counter clockwise from a central storting position. Alternatively, the grounding of a pin that is engaged with a short portion, for example, 20 degrees, of a thread ramp on the rotor 104 would cause

the required rotation of the during the first portion the rod travel before the rotor 104 engages axially with the columns 106,108.

The device 416 may be provided with more than two columns 106,108, and consequently a more complicated rotor 104, so as to provide a range of resistive forces based upon various combinations of column strength. The columns 106,108 and rotor 104 may be configured so as to be replaceable so as to enable the device 416 to be recommissioned after use thereof

Figures 13 to 18 show a further embodiment of a force absorption device generally designated 516 which incorporates selectably movable pistons. As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals. Figure 13 shows a cylinder 24 having first and second pistons 26a, 26b, arranged around a common rod 18. It will be noted that the apertures 28a of the first piston 26a are of a narrower bore than the apertures 28b of the second piston 26b and thus appreciated that the resistive force to movement of the rod 18 generated by the first piston 26a is greater than the force generated by the second piston 26b. For example, the apertures 28a of the first piston 26a may be dimensioned such that a resistance of 90 kN is provided, and the apertures 28b of the second piston 26b dimensioned such that a resistance of 60 IcN is provided. The pistons 26a,26b may be selectively coupled to the rod 18 such that either the second piston 26b, or both the first and second pistons 26a,26b, are carried by the rod 18, and a resistance of either 60 kN or 150 kN is provided.

Figures 14 and 15 show two different manners in which a piston 26a can be selectively coupled to the rod 18. Figure 14 shows a rod 18 which is provided with pivotable arms 122. The arms 122 are pivotably mounted to the rod 18 at a first end 124 and are movable between a deployed position shown in figure 14 and a stowed position. In the deployed position, the ends 126 of the arms 122 distal to their pivotable mountings are received in a seat portion 128 of the piston 26a. Ih the stowed position, the distal ends 126 of arms 122 are disengaged from the seat portion 128, and the arms lie against and substantially parallel to the rod 18. The rod 18 and arms 122 are thus able to pass

through a central aperture 130 of the piston 26a which is surrounded by the seat portion 128. A mechanism suitable for the movement of the arms 122 is described with reference to figures 16 to 18. Figure 15 shows a selective engagement arrangement wherein balls or rollers 132 are provided between respective ramp surfaces 134,136 of the rod 18 and piston 26a. Movement of the rod 18 through piston central aperture 130 drives the rollers against a stop 138 of the piston 26a and hence couples the rod 18 to the piston 26a.

Figures 16 to 18 show a device 516 which embodies the deployable arm arrangement of figure 14. The arms 122 are connected to a deployment mechanism 140 which is operable to deploy the arms 122 at differing positions of the stroke of the rod 18. The mechanism 140 includes concentric inner and outer coils 142 _S 144 mounted in an end of the cylinder 24 and corresponding concentric inner and outer ferric rings 146,148 provided within the cylinder 24. The inner ring 146 includes an extendable connector 150 provided between the ring 146 and arms 122. The outer ring 148 includes and extendable stop 152. The connector 150 is provided with a projection 154 which is engageable by the stop 152.

Figure 16 shows the device 516 in an initial rest position with neither coil 142,144 energised and the arms 122 in the stowed position. It will be appreciated that neither piston 26a,26b is connected to the rod 18, and that the application of a force 86 to the rod 18 will result in movement of the rod 18 into the cylinder 24 without experiencing any appreciable resistive force.

Figure 17 shows the device 516 with the outer coil 144 energised. The rod 18 is able to move through the pistons 26a,26b until the connector projection 154 contacts the outer ring stop 152. This causes deployment of the arms 122 and couples the second piston 26b to the rod 18.

Figure 18 shows the device 516 with the inner coil 142 energised. Movement of the rod 18 causes deployment of the arms 122 in advance of the first piston 26a, with the

result that the first piston 26a is moved by the rod 18, and the second piston 26b is moved by contact with the first piston 26a.

Figures 19 and 20 show a further embodiment of a force absorption device generally designated 616 which incorporates selectably movable pistons. As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals. The device 616 includes a piston to rod coupling arrangement generally designated 156. The arrangement 156 includes concentric inner and outer coils 142,144 mounted in an end of the cylinder 24 and corresponding concentric inner and outer ferric rings 146,148 provided within the cylinder 24. Each ferric ring 146,148 is. provided with an extendible connector 150 which is provided between the ring 146,148 and a concentric end boss 158, 160 of the rod 18. Each connector 150 includes a tubular portion 162 comprised of a contracting mesh. The mesh portion 162 of each connector 150 surrounds a skirt 164a, 164b of each piston 26a,26b. The mesh portion 162 is configured to reduce in diameter when placed in tension and thus grip the piston skirt 164a,164b, thereby coupling the rod .12 to a piston 26a,26b by a factional connection. The mesh portion 162 Figure 19 illustrates the situation where neither coil 142,144 is energised, and hence the rod 18 is movable through the cylinder 24 independently of the pistons 26a,26b. In figure 20, the outer coil 144 is energised with the result that the second piston 26b is coupled to the rod 18. By energising the inner coil 142, the first piston 26a would be coupled to the rod 18 and the second piston 26b movable by contact with the first piston 26a.

Figures 21 to 23 show a further embodiment of a force absorption device generally designated 716 which incorporates a tapered piston and a variable diameter . As before, features common to the force absorption devices described with reference to the preceding figures are identified with like reference numerals.

The device 716 comprises a hydraulic cylinder 24 within which there is provided a tapered piston 166 movable through a control orifice 168. The diameter of the control orifice 168 may be varied by the introduction differently dimensioned annular control rings 170 into the control orifice 168, In use, the control orifice 168 is closes as the

piston 166 moves therethrough. The taper of the piston 166 is chosen such that the deceleration of the piston 166 as it moves through the cylinder 24 results in a substantially constant flow rate of fluid through the orifice 168. This in turn provides a substantially constant resistive force. The magnitude of this force can be selected as a function of the control orifice diameter. The taper of the piston 166 is an exponential curve. A cylinder of the type described with reference to figures 21 to 23 may be used in conjunction with a pressure relief valve of the type described with reference to fϊgures.2 to 5.

The force absorption devices described above may be used in conjunction with a control and activation system of a vehicle which is operable to determine the imminent likelihood of a collision and then configure the force absorption device in anticipation of the estimated force to be applied to the bumper beam. The system may be configured so as to be able to change the resistive force provided by the absorption device during a collision event.

The above described embodiments disclose force absorption devices for a vehicle bumper beam which are operable to provide differing resistive force to a force applied to the beam. The devices may be split into two groups comprising multiple discrete force devices and variable force devices. The devices are configured such that they may be reset after a collision event either by an internal restorative mechanism, or by the replacement of sacrificial components.