BACKGROUND ART It is known that workmen repairing or widening carriageways are at risk of death or serious injury from accidental impacts with vehicles using the carriageways.

As a result, relatively massive objects, usually lorries, are positioned on the carriageways to shield the workmen from such impacts. However, this gives rise to another problem, and a health and safety regulation has been introduced requiring the use of energy absorbing structures on the relatively massive objects, e. g. in the form of lorry mounted crash barriers, to protect occupants of a vehicle which may be in collision with the relatively massive objects.

Such lorry mounted crash-barrier cushions (or truck-

mounted attenuators) are known from EP 1,001, 091 and US 6,244, 637. These publications describe barriers comprising a frame of hinged arms which together define two bays in which energy absorbing elements are disposed. Restraints are provided on the hinges to resist movement of the hinges. On impact, the restraints break, allowing the frame to collapse and compress the energy-absorbing element.

DISCLOSURE OF INVENTION According to a first aspect of the invention, there is provided a crash barrier for deployment on a mobile body, comprising: a support member for attachment to the mobile body; a bumper spaced from the support member for engaging a vehicle during impact with the crash barrier; a linear guide system for guiding the bumper towards the support member during impact; and an energy absorber configured to absorb impact energy as the bumper is guided towards the support member; wherein the guide system comprises first and second elongate members, one end of each being pivotally coupled at a variable acute angle to the support member, and a third elongate member pivotally coupled to the first and second members to define with the support member a parallelogram with variations in magnitude of the acute angle determining separation between the third and support members.

The present applicant has appreciated that the parallelogram framework has a number of advantages as a linear guide system. Firstly, it can be retracted for ease of transportation or storage. Furthermore, it may readily

be configured to be strong enough to resist damage in an impact without interfering with the performance of the energy absorber. The parallelogram framework may be aligned horizontally at least when the linear guide system is deployed. In this way, the parallelogram framework will pivot in such a way that the third elongate member will be urged laterally relative to the crash barrier, substantially perpendicular to the impact direction.

The guide system of the crash barrier may further comprise at least one further elongate member pivotally coupled to the parallelogram (e. g. the third elongate member) at a variable angle. The at least one further elongate member may also be pivotally coupled (directly or indirectly) to the bumper. The at least one further elongate member may define with the third elongate member part of another parallelogram framework arranged in series with the aforementioned parallelogram (hereinafter referred to as the"first parallelogram"). The two parallelograms may be substantially parallel, perhaps even aligned in a common plane. The two parallelograms may be of equal size, with one being arranged as a mirror image of the other (i. e. with the third elongate member acting as a mirror plane).

The guide system of the crash barrier may comprise at least one further array of elongate members arranged in an equivalent manner to the first, second and third elongate members, with each at least one further array of elongate members defining with the support member a respective

additional parallelogram. One of the respective additional parallelograms may be arranged to one lateral side of the first parallelogram, and may be arranged as a mirror image of the first parallelogram. Each parallelogram may be configured so that a respective part is urged laterally away from a corresponding part of the other parallelogram during an impact. Such side-by-side symmetry may help to balance the guide system. The first parallelogram and its mirror image may each be pivotally coupled via respective elongate members to a common support. In this way, the common support may be constrained to move linearly towards the support member during an impact, even though parts of the two parallelograms disposed therebetween are urged laterally.

At least one of the respective additional parallelograms may be arranged in a plane parallel to but spaced from that of the first parallelogram. The energy absorber may be disposed in spacing between respective planes of the parallelograms. Such an arrangement above- and-below the energy absorber may further balance the guide system, helping to resist any upward force impacted on the bumper during impact.

The energy absorber may be sacrificial i. e. may deform permanently when absorbing energy from an impact. In other words plastic not elastic deformation may occur. The energy absorber may comprise a honeycomb structure, e. g. a cellular structure having an array of cells of hexagonal cross-section. The cells may be aligned with their axes

parallel to a notional line extending between the support member and bumper. Advantageously, the guiding system may be configured to maintain during impact a predetermined orientation between the bumper and the energy absorber.

Thus, the guiding system helps to control the direction of the impact on the honeycomb structure, enabling impact forces to be directed parallel to cell axes-the optimum direction for energy absorption in the honeycomb structure.

The properties of the sacrificial energy-absorber (such as the material, cell size and cell wall thickness) may be selected to provide a level of energy absorption appropriate for the conditions in which the crash barrier is used. For example, if the crash barrier is for use on motorways or other high speed roads (e. g. having speed limit of 70mph), the energy-absorber may need to deform more readily than one deployed in a crash barrier for use in built-up areas or other low speed roads (e. g. having speed limit of 30mph). In this way, impact forces experienced by vehicle occupants colliding with the crash barrier may be reduced to tolerable levels.

Alternatively, the energy absorber may be re-usable and configured to survive the impact. The energy-absorber may comprise a disc brake or the like which may be mounted to resist pivotal movement of the elongate members relative to each other or relative to the support member.

The disc brake may be mounted at the joints connecting the first and second members to the support member or to the third elongate member.

The energy-absorber may comprise a fluid actuator, such as a hydraulic ram, configured to control separation between the third and support members. For example, the fluid actuator may be disposed along one diagonal of the first parallelogram. By providing the fluid actuator along a diagonal rather than along the sides of the framework, the length of the actuator is maximised. The fluid actuator may be configured to retract and deploy the parallelogram framework for storage/transportation and active use respectively.

The fluid actuator provides a resistance to a change in separation between the third and support members which would result from an impact. The resistance provides the mechanism for energy absorption during the impact. The resistance may be uniform per unit change in separation between the third and support members. Different levels of resistance may be chosen to suit characteristics of potential impacts. Alternatively, the resistance may vary with increasing change in separation between the third and support members. The resistance of the hydraulic actuator may even be controlled dynamically, for example in dependence on information sensed during an impact.

The fluid (e. g. hydraulic) actuator may be configured to have increased resistance below a threshold speed and decreased resistance above the threshold speed. In other words, the hydraulic actuator may act as the energy absorber in a strengthening assembly of a variable bumper system of the kind taught in WO 02/057119. Such a variable

bumper system addresses the conflicting requirements of a bumper system, namely it must be stiff enough to withstand impacts at low speed without compromising the safety of a pedestrian in higher speed collisions.

Bumper deformation resistance may be increased by more than 50%, perhaps even 100%, below the threshold speed. The threshold speed may be approximately 5 mph. In this way, the bumper system will be more rigid at so-called"parking speeds"where minor vehicle-to-vehicle bumps are common, than at so-called"around town speeds"of about 30 mph.

In a variable bumper system, there may be limited space. The linear guide system may comprise at least one array of only two parallelogram frameworks which are connected in series. The system may comprise more than one array mounted in parallel. Each array may comprise a first parallelogram framework which is connected to the bumper and to a second parallelogram framework connected to the vehicle. A hydraulic actuator may be connected along a diagonal of the first or second framework. Alternatively, a reusable energy absorber, such as a disc brake may be used to resist deformation of the parallelogram frameworks.

The bumper, which in use will engage a vehicle during impact with the crash barrier, may be configured to prevent the vehicle slipping under the linear guide system. The bumper may comprise a sacrificial member configured to deform during impact. The sacrificial member may be configured to adopt a profile during deformation which corresponds to that of the object colliding therewith.

Such a sacrificial member may help to improve transfer of forces imparted by the object to the guide system and energy absorber.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention specific embodiments will now be described, purely by way of example, with reference to the accompanying drawings in which: Figure 1 shows schematically a perspective view of a crash barrier embodying the present invention; Figure 2 shows schematically a side view of the crash barrier of Figure 1; Figure 3 shows schematically a plan view of the crash barrier of Figure 1, with a different energy absorber; Figures 4a and 4b show schematically a plan view of part of the crash barrier of Figure 1, respectively before and during impact; Figure 5 shows a schematic view of a bumper system, incorporating a crash barrier embodying the present invention, and Figure 6 is a schematic view showing the detail of the bumper system of Figure 5.

DETAILED DESCRIPTION OF DRAWINGS Figure 1 shows a crash barrier (10) according to a first embodiment of the present invention. The crash barrier (10) comprises a support member (12) for attachment to a mobile body, such as the front of a lorry, and a bumper (14) spaced from the support member (12) for

engaging a vehicle colliding head-on with the crash barrier (10) (see arrow A). A linear guide system (16) couples the bumper (14) to the support member (12), and is configured to guide the bumper (14) along a linear path towards the support member (12) during a head-on collision as energy absorber (18) absorbs impact energy by deformation. The linear guide system (16) comprises a framework of elongate members or rods (20), including first and second elongate members (22,24) pivotally coupled at a variable acute angle (a) to the support member (12). For example, angle (eux) may be in the range 80° to 10°, perhaps 75° to 25°. A third elongate member (26) is pivotally coupled to each of the first and second members (22,24) to define with the support member a framework parallelogram (28) (shown in bold). The separation between the support member (12) and the third elongate member (26) (along a notional line extending between the support member (12) and the bumper (14)) varies with the magnitude of acute angle (a).

As shown in Figure 1, the framework parallelogram (28) is aligned in a horizontal plane. In the same horizontal plane, two further elongate members (30,32) are pivotally coupled to the third elongate member (26) and define part of another framework parallelogram (34) arranged in series with parallelogram framework (28). The framework parallelograms (28, 34) are equal in size with one being arranged as a mirror image of the other, with member (26) acting as the mirror plane. Further"pairs"

of parallelogram frameworks are provided in series to establish a pivotal connection to bumper (14).

As also shown in Figure 1, the linear guide system (16) comprises at least one further array of elongate members arranged in an equivalent manner to the first, second and third elongate members (22,24, 26). The further array of elongate members defines with the support member (12) a respective additional parallelogram framework (28'). The respective additional parallelogram framework (28') is a mirror image of parallelogram framework (28), about a notional central line extending from support member (12) to bumper (14). The parallelogram framework (28') is pivotally coupled to elongate members which define part of another framework parallelogram (34') which mirrors framework (34). In fact, parallelogram frameworks (34, 34') are linked by common support (40), forming one side of each. In this way, as guiding system (16) guides bumper (14) towards support member (12), the common support (40) will be constrained to move directly towards support member (12). In contrast, elongate member (26) (and its counterpart (26')) will be urged outwardly in the direction of arrows B.

As shown in Figure 2, the guiding system (16) also comprises a framework of elongate members (20) below the energy absorber (18). The upper and lower parts (50,52) of guiding system (16) may be identically configured, with extremities of each"pair"of framework parallelograms coupled by connectors (54). In this way, an open-lattice

box-structure is created which provides increased resistance to impact forces acting to deflect the guidance system from its linear path. The energy absorber (18) (e. g. one or more blocks of honeycomb structure) is shorter than the maximum separation between support member (12) and bumper (14), with gap (56) provided between bumper (14) and energy absorber (18). As shown in Figure 1, a honeycomb structure would be deployed with the columnar or central axis of the hexagonal cells aligned parallel to a notional line extending between the support member (12) and bumper (14).

Figure 3 shows an alternative crash barrier (10') which employs the same linear guide system (16) as Figures 1 and 2. Instead of a sacrificial energy absorber (18), a fluid actuator (60) is provided along a diagonal of parallelogram framework (28'). The fluid actuator (60) (e. g. hydraulic ram) provides a resistance to outward movement (arrow B) of corner region (62). This in turn provides resistance to linear movement of common support (40), which in turn provides resistance to outward movement (arrow B) of third elongate member (26). The resistance of fluid actuator (60) may be pre-determined at a uniform level, or may be dynamically controlled by controller (64), acting in dependence upon information received from sensor (66) about impact.

Figures 4a and 4b show schematically the positions of two pairs of parallelogram frameworks (28,34) before and after impacts. During impact, the longitudinal extent of

length"L"of the guide system (16) is reduced without plastic deformation of the elongate members (20). Impact energy is absorbed by energy absorber (18) or fluid actuator (60).

Figure 5 shows schematically a bumper system (70) embodying the crash barrier invention in context with a variable bumper system for a car (72). The bumper system (70) comprises a crash barrier or bumper (74) having a protuberant profile defining a front surface (76) which is intended to make first contact with an obstacle (e. g. car or pedestrian) during a collision. The bumper system (70) also comprises a strengthening assembly (78) for in use reinforcing the front surface (76) of the bumper (74) to increase bumper deformation resistance. The strengthening assembly (78) is controlled by a controller (80) in dependence upon vehicle speed sensed by sensor (82). If vehicle speed is below a threshold level, the controller (80) activates the strengthening assembly (78) so as to increase the stiffness of the front surface (76) of the bumper (74).

Figure 6 shows schematically a part of the bumper system (70) of Figure 5. The strengthening assembly (78) comprises a linear guide system which is similar to that of Figure 3 and which is pivotally coupled to a support member (12) by which the linear guide system is attached to the car. Since there is limited space, perhaps only a depth of 200mm, the linear guide system comprises two arrays of framework parallelograms (28, 28') each having a

pair of parallelograms mounted in series. One parallelogram of each pair is arranged as a mirror image of the other, with members (26, 26') acting as the mirror plane. The arrays of framework parallelograms (28, 28') are arranged in parallel (i. e. side-by-side) with one pair being arranged as a mirror image of the other pair about a notional central line (84) extending from support member (12) to bumper (74). All the parallelograms (28, 28') are equal in size.

A first parallelogram framework of each pair is pivotally attached to the bumper (74) and a second parallelogram framework of each pair is pivotally attached to the support member (12). The first framework is provided along its diagonal with a fluid actuator (60). The fluid actuator (60) (e. g. hydraulic ram) provides a resistance to outward movement (arrow B) of corner region (62). The fluid actuators (60) are connected to the controller (80) which is configured to control the resistance to this outward movement provided by each fluid actuator. For example, the controller (80) is configured to decrease the resistance once the speed exceeds the threshold value. The strengthening assembly always remains concealed behind the leading surface of the bumper.

In an alternative arrangement, the fluid actuators (60) may be replaced by another reusable energy absorber, such as a disc brake (100). The disc brake (100) shown schematically in just one possible location in Figure 6, may be arranged to resist any change in corner angles of

parallelograms (28, 28'). For example, the disc brake may be positioned adjacent one corner of one parallelogram (28, 28') to control angular separation between two sides pivotally connected at that corner.