EP0757132B9 - Bridge element, especially for surmounting gaps by vehicles and system for transporting and placing the bridge element - Google Patents

Description

The present invention relates to a span structure intended in particular for crossing breaches by vehicles, such as armored vehicles of the engineering, and a transportation system on a vehicle of at least at least two bridging bridges intended for crossing of breaches and removal of spans above breaches from the vehicle.

We know systems for filing from of a vehicle a span of short length or more long length after two or more end-to-end assembly more short span.

Such a system is described in document FR-A-2 683,837 in the name of the plaintiff and includes basically a support and launch beam a movable span or assembled span relative to the vehicle to a cantilever position ; means for moving the span or spans assembled relative to the beam at one cantilever position at the front of the beam; and one plate supporting in a guided way the beam and being able tilt relative to the vehicle with the beam to allow removal of the span (s) assembled over a breach to be crossed.

In the inactive or transport position on the vehicle road, the beam has its part behind the platform support housed between two superimposed spans and the connecting arm forming spacers of the two spans, each U-shaped hinged at its ends respectively to two internal side walls of two central boxes of two span elements. Both link arms of the lower span occupy a folded or lowered position to increase the beam accommodation space and these arms of link can be taken up simultaneously by a lift table at a substantially parallel position to the vehicle chassis, to which they are locked at the lower span.

The above known system thus has the disadvantage major to require a complex table structure lifting mounted on the vehicle chassis and means associated command to raise it from a inactive position, after removal of the beam above the lower span, and acting on the lower ends of the U-shaped link arms of this span to separate them from each other until their locking position at the lower span.

The object of the present invention is to eliminate the above drawback of the known system by proposing a span structure intended in particular for vehicle breaches such as armored engineering vehicles, comprising two elements span parallel to upper raceways and linked together by two link arms forming spacers, and which is characterized in that each link arm is approximately Ω shaped of which the two basic coaxial elements are made up by axes having each of their ends connected to the body of the corresponding span element by a ball joint; each articulated axis is mounted at rotation, opposite its ball joint, in a bearing immobilized in rotation to the body of the element of span and able to slide relative to this last so as to allow movement of the axis articulated in a plane perpendicular to the elements of works around the center of articulation of this axis; and in that means are provided for recalling automatically each link arm in its position normal use in a plane substantially perpendicular to the two span elements and maintain the link arm in this normal position of use.

Preferably, the means for recalling and maintaining each link arm includes two cams identical parallel integral with the link arm respectively at the two ends of the articulated axes opposite the ball joints and whose axes of rotation are coaxial with the axes of rotation of the axes articulated; two rollers held in abutment by a means elastic on the bottom of the shape offset of each cam following an effort ensuring the maintaining the link arm in its normal position of use, the eccentric shape of the cam being such as during a rotation of the link arm in one way or the other, one or the other of the two rollers exerts on this cam a righting torque of the link arm to its normal position.

The two aforementioned rollers are mounted on a yoke joint integral with one end of a support axis sliding mounted in a fixed box secured to the body of the corresponding span element and the means said elastic includes a pre-stressed spring housed in the fixed box and working on the support axis a holding force of the two rollers or of one or the other of these resting on the periphery lower of the corresponding cam.

Advantageously, the lower part of each cam where are in support simultaneously the two rollers correspondents is plane and is located between two symmetrical parts of the eccentric shape of the cam.

Preferably, the abovementioned bearing is a block parallelepiped in a rectangular window block guide made in the element body span corresponding perpendicular to the axis longitudinal of it.

Each ball joint includes a nut support of the female sphere in which the male sphere integral with the end of the articulated axis corresponding, the support nut being itself fixed in an integral support piece, for example by welding, of the body of the span element corresponding.

The span structure also includes, associated with each of the two link arms, at least two stops integral respectively with the two span elements and on which can support the arm of corresponding link in the folded position thereof.

Each link arm comprises, integral with the central connection part of the Ω, two pairs of rollers each extending parallel to the structural elements.

Protective rubber bellows are provided to hermetically seal the passages between bearings and rectangular guide windows.

In the normal position for using a link arm, the two prestressed springs associated with it are at their maximum length.

The invention also provides a transfer system on a road vehicle, such as a truck, at least two bridging bridges superimposed on a chassis of the vehicle that can be assembled end-to-end, and removal of each span or span assembled end-to-end over a gap in cross, each span having a structure such that defined above, and of the type comprising a beam supporting and launching a span or span assemblies movable relative to the vehicle towards a cantilever position; means of moving the span or spans assembled relative to the beam at a cantilever position at the front of the support and launching beam; and a tray guided support of the beam and capable of tilt relative to the vehicle with the beam to allow removal of the span (s) assemblies, and which is characterized in that, when removing the span or assembled span, the end of this span or these span opposite assemblies to that already supported on the bank from the gap opposite to the road vehicle, is supported at the end of the removal and launching beam by the rear link arm of the two elements of span of the span or the rear span of the spans assembled during the tilting of the beam until the removal of said span end or spans assembled on the bank adjacent to the vehicle road, the link arm resting on the beam removal that can pivot relative to the elements of spans around the articulated axes so that the arm can adapt to different inclinations of the laying beam.

In the transport position on the road vehicle, the laying and launching beam is arranged between two overlapping spans and the connecting arms of two span elements of the lower span occupy a folded position under the removal beam and launching by being in contact with it by the rollers of the arms of liaison.

The two folded link arms are also support on the integral stops of the elements of spans.

The link arms are straightened to their position normal by the return means exerting the torque of straightening on these, after removal of the beam from removal and launching between the two spans superimposed.

Means of moving the span or span assembled relative to the laying beam and launch include an endless chain drive extending along the longitudinal axis of the beam and mounted on at least two gears extremes themselves rotatably mounted on the beam; and at least two integral fork elements of the drive chain and able to grasp the game center of a link arm between the two pairs of rollers of this arm bearing on the beam removal and launch.

The invention will be better understood and other aims, details and advantages of it will appear more clearly in the description explanatory which will follow made with reference to attached schematic drawings given only as a example illustrating an embodiment of the invention and in which:

Figure 1 is a cross-sectional view representing three overlapping spans in position of transport on a road vehicle.

Figure 2 is a half top view along the arrow II of figure 1.

Figure 3 is a sectional view along line III-III in Figure 2.

Figure 4 is an enlarged sectional view of the part circled in IV of Figure 1.

Figure 5 is a side view along arrow V of Figure 4.

Figure 6 is a half-sectional view along the line VI-VI of figure 4.

Figure 7 is a perspective view showing schematically the assembly of a link arm between two span elements.

Figure 8 is a view along arrow VIII of the Figure 4 with a link arm of two elements of works in the folded position.

Figure 9 is a sectional view along line IX-IX in Figure 8.

Figure 10 is a schematic side view of means of straightening a link arm of elements of travures to its normal position.

Figure 11 is an enlarged cross-sectional view of the central part of figure 1.

Figure 12 is a sectional view along line XII-XII in Figure 11.

Figure 13 is a side view of the removal beam and launching of a span represented in particular in figure 11.

Figure 14 is a sectional view along the line XIV-XIV in Figure 13.

Figure 15 is a sectional view along line XV-XV in Figure 13.

Figure 16 is a partial sectional view along the line XVI-XVI of Figure 14; Figure 16A is a perspective view along arrow 16A of the figure 16.

Figures 17A to 17F show some of the different phases of laying of spans assembled above a breach to cross.

Figure 18 shows in cross section the configuration of two cross members supported by a bank of different levels from a breach.

Referring to the figures, reference 1 designates a road vehicle, such as a truck, for transport to a breach 2 to be crossed by vehicles, such as for example armored vehicles of engineering, three works respectively upper 3, intermediate 4 and lower 5 superimposed on a longitudinal chassis 6 of the vehicle.

Vehicle 1 supports a system adapted to deposit separately the span 3, 4, 5 above the gaps or assemble end-to-end at least two spans and lay the spans assembled above a breach.

The system of assembly of spans and removal of these are generally identical to that described in the French patent N ° 2,683,837 incorporated here for reference and therefore will not be discussed in detail, apart from the few differences that will appear later in this description.

Spans 3, 4, 5 are identical and are each formed by two parallel span elements 3a, 3b; 4a, 4b; 5a, 5b interconnected by two arms of link forming spacers 3c, 4c and 5c. Each arm link can be folded down from its position normal use at a position allowing the passage of a beam 7 for launching and removing span as shown in Figures 1 and 11. These Figures thus show that the link arm 4c of the intermediate span 4 occupies a folded position or lowered so as to increase relative to the arm of connection 3c of the upper span 3 the height of housing the beam 7 in the rest position or inactive on the vehicle 1.

The two span elements of each span 3, 4, 5 have two parallel tracks superior 3d, 4d and 5d and each element of span includes a rigid central body or box 8 and two access nozzles 9, 10 assembled respectively to the two ends of the central box 8 so as to extend the upper track of this box. Beak access 9 is fixed to a part of the central box 8 by a transverse pivot axis 11 and to a part opposite of this box by locking means 12 by a transverse pivot axis 11 and to a part opposite of this box by locking means 12 which are unlockable so as to allow the spout 9 occupy a low position shown in Figure 3 in the case where only one span 3; 4; 5 must be deposited above a breach or a raised position as can be seen from the assembled structures 3, 4, 5 at Figures 17A-F and to which the raised beak 9 of the span is fixed by locking means suitable on another fixed spout 10 of a span adjacent to form a larger span length.

The locking means of each lifting spout 9 a span in the corresponding box 8 thereof and the locking means of each raised access spout 9 to a fixed nozzle of another adjacent span can be of the kind described in the French patent No. 2,683,837. These locking means can also be made up of those that have been described in French patent application No. 95 09 432 filed August 2, 1995 in the name of the plaintiff and incorporated here for reference.

The two elements of a span 3; 4; 5 are assembled by their link arm so that the span can have at each of its ends two respectively mobile and fixed access nozzles 9 of so that there is no taxation for the meaning of presentation of the spans during their coupling.

Each span 3; 4; 5 additionally includes two pairs of front and rear rollers 14 fixed in screws with screw at the two internal side walls opposite of each other respectively of two elements of spans. The rollers 14 allow the displacement of the corresponding span along the laying and launching beam 7 while rolling on two guide rails 15 formed respectively by two lateral shoulders of the beam 14 made at its the top part.

According to the invention each link arm is approximately in the form of Ω located, in position normal use shown in Figures 1 and 11 for upper and lower span 3 and 5, in a plane substantially perpendicular to the axes longitudinal of the two span elements correspondents. The two coaxial elements of the base Ω are constituted by axes 16 transverse to two corresponding span elements in position normal use of the associated link arm and which are each connected to the body of the box 8 of an element of span, in this case element 3a of the span 3 as shown in FIG. 4, by an articulation with ball joint 17 comprising a nut 18 for supporting the female sphere 19 in which the sphere is housed male 20 secured to the end of the articulated axis 16, the support nut 18 being itself fixed in a support female part 21 secured, for example by welding, of the body 8 of the span element 3a. The nut 18 is fixed in the support piece 21 by via a screw 22 coaxial with the articulated axis 16 and the head of which is housed in a bore 23 at the end of axis 16.

Each articulated axis 16 of a link arm is mounted at rotation, opposite its ball joint 17, in a bearing or pad 24 constituted by a block generally parallelepidic immobilized in rotation relative to the body 8 of the span element in a rectangular window 25 made in the body 8 perpendicular to the longitudinal axis of the element span and in which the bearing 24 can slide. Each window 25 is made in the veil longitudinal 8a of the body 8 of the span element of so that the bearings 24 return the forces longitudinal exerted on the axes 16 in the sails longitudinal 8a of the body 8. The ball joint 17 and the bearing 24 of each articulated axis 16 allow thus a free rotation around its axis of rotation OX and a vertical displacement of it along the axis orthogonal OZ, as symbolized in figure 4, of the arm of corresponding link 3c, 4c and 5c. In other words, each axis 16 can rotate around the OX axis and can be move around the C articulation center of the ball joint 17 in a perpendicular plane to the corresponding span element, as we will see later in certain cases of use of spans.

A rubber bellows 26 is hermetically fixed around the outer end of the bearing 24 and at longitudinal web 8a of body 8 in a housing appropriate of it so as to protect the interior body 8 of the beam against dirt, such as than mud.

Each span element also includes means to automatically recall each arm of connection of two span elements at its position normal use and maintain the arm at this position.

These means include two identical parallel cams 27 secured to the corresponding link arm 3c, 4c, 5c at the two ends of the opposite articulated axes 16 to the ball joints 17. The axis of rotation of each cam 27 is coaxial with the axis of rotation of the axis 16 and the eccentric shape of the cam 27 extends around from the axis 16 on about 270 ° of angle as it is better visible in Figure 5 by being symmetrical by relation to the median plane transverse to the element of corresponding span passing through the articulated axis 16.

The means of recalling and holding each arm of link also include two rollers 28 with axes of rotation 29 parallel to the axis of rotation of the axis articulated corresponding 16 and held elastically in support on the lower part 27a of the form eccentric of the cam 27 following an effort ensuring the stable maintenance of the corresponding link arm 3c, 4c, 5c at its normal position. Eccentric shapes respectively of the two cams 27 associated with an arm of bond are such that when rotating this arm in one direction or the other around the OX axis, one either of the two rollers 28 exerts on each cam corresponding 27 a straightening torque of the arm of bond corresponding to its normal position as we will see later.

The two rollers 28 are mounted on a common yoke 30 integral with one end of a mounted support pin 31 sliding in a fixed housing 32 secured to the veil 8a of the body 8 of the span element corresponding by a fixing flange 33. As shown in Figure 4, the axis 31 is perpendicular to the axis of rotation OX of the corresponding articulated axis 16 and a prestressed spring 34, constituting the means elastic now resting the two rollers 28 on the cam 27, is housed in the fixed housing 32 substantially coaxial with the support axis 31 which is shown in the upper upper position corresponding to the maximum elongation of the spring 34. As shown in particularly Figure 5, the lower part 27a of each cam 27 where the two are supported simultaneously corresponding rollers 28 in normal position of the connection is flat and is located between the two parts symmetrical of the eccentric shape of the cam 27.

Figures 8, 9 and 11 show that at least one of span 3, 4, 5, in this case the span intermediate 4, also includes two pairs of fixed cylindrical rubber stops 35 respectively to the two facing sails 8a of the two elements 4a and 4b of span 4 with the two stops 35 of each pair located symmetrically on the plane orthogonal to the longitudinal axis of the span element corresponding and passing through the axis of rotation OX of the link arm 4c. Each stop 35 is fixed to a fixing lug 36 fixed perpendicularly to a plate 37 secured to the veil 8a by fixing screws 38. The cylindrical stops 35 of the same pair are attached to their respective legs 36 so that their longitudinal axes are inclined relative to the plane of symmetry. In addition, the two stops 35 being face respectively of two span elements are positioned relative to these structural elements of so that the corresponding link arm comes in support, in its low folded position on these two stops 35 while being inclined relative to the plane of symmetry a predetermined angle value, for example about 55 ° as shown in Figure 8. The setting stop of the link arms 4c of the span intermediary has the advantage of locking (or wedge) vertically this same span under the launching beam and at the same time the span lower (held in the ascending vertical direction).

Each link arm 3c, 4c, 5c partly comprises center of the upper branch of the Ω shape of this arm, two pairs of rollers 39 to avoid friction between the part central link arm and the top of the laying and launching beam 7 during a relative displacement of this beam and the arm of liaison. The two rollers 39 of a pair are fixed on 4th yokes attached to the link arm corresponding by extending perpendicular to the central part of this arm. As shown in figure 12, the two connecting arms 4c of the span intermediate 4 are held in abutment by the rollers 39 on corresponding lower parts of the beam 7 by the righting torque of each arm exerted by one of the rollers 28 on each cam corresponding 27. When the beam 7 is released from its storage position between the two spans upper 3 and intermediate 4 during the launching and removal of one or more assembled structures above a breach, the link arms 4c of the intermediate span 4 automatically resume their normal vertical position. Figure 10 shows the phase of raising a link arm according to the direction of rotation indicated by arrow F1 after removal of the beam 7. In this figure, one of the rollers 28 is supported by the pre-stressed spring 34 on the cam corresponding 37 at a distance d from the plane of symmetry defined above so that this roller 28 exerts a righting torque C = F x d, where F is the force exerted by the prestressed spring 34 on the roller 28 in contact with cam 27.

The means of displacement of the beam 7 towards its cantilever position relative to the vehicle Road 1 are the same as those described in the French Patent No. 2,683,837 and therefore do not have to be described.

Similarly, the means of moving a span or spans assembled relative to beam 7 thus that the plate means P carrying in a guided manner the beam 7 and allowing its tilting relative to the vehicle to allow the removal of a span or assembled span can be identical to those described in French Patent No. 2,683,837.

However, Figures 13 to 15 show a mode of particular realization of means allowing the translational movement of a span or span assembled on the beam 7.

These means include an endless chain drive 40 extending along the longitudinal axis from the beam 7 passing over toothed wheels 41 to the as shown in figure 13, mounted in rotation on the structure of the beam 7. The chain 40 is directly trained appropriately for a electric motor (not shown) mounted on the platform tilting P. The means of moving a span relative to beam 7 also include at at least two fork elements 42 integral with the upper strand of the drive chain 40 and suitable to grasp the central part of one of the two arms of connection of a span, in particular the link arm rear, during the launch phase of the span. Preferably, two pairs of elements forming fork 42 are provided arranged symmetrically at transverse median plane of beam 7 while being located between the two pairs of rollers 39 of the same link arms. Figure 14 shows two pairs fork elements that can also be attached to the lower strand of the chain 40 of so as to train two or more assembled spans. As shown in Figure 17, two elements forming fork 42 located on the same side in the direction transverse of the chain 40 are rotatably mounted respectively at the two outer ends of an axis 43 connecting parallel links 40a of the chain 40 and are recalled in projecting position above the upper strand of the chain 40 by a spring in spiral 44 mounted on the axis 43 in the middle of it. Each fork element 42 includes a inclined part 42a allowing it to be folded down by a central part of a span link arm when moving in the appropriate direction of the chain 40 to enter this central part in order to carry out the launching and removal phases of the span where assembling it to another span.

The principle of removing a span or two or three spans assembled end to end is in a way general identical to that described in the patent French N ° 2,683,837, but certain phases of launch and removal of a span or span assemblies have been shown in Figures 17A to 17F to highlight certain features related to the invention.

Figures 17A to 17F show the removal of three spans assembled end to end 3, 4, 5.

At the configuration shown in Figure 17A, the beam 7 occupies its cantilever position on the platform tilting P relative to the vehicle 1. In this configuration, the long span made up by the spans 3, 4, 5 is supported on the beam of launch 7 via the rollers 39 of the arms link 5c of span 5 so that this last keeps its geometry like the one shown in figure 1. This geometry is made possible by the fact that the prestressing force exerted by the springs 34 associated respectively with cams 27 of link arm is significantly greater than the effort of reaction exerted on the link arm.

FIG. 17B shows that the plate P has been tilted from so as to deposit the end of the large span length on the bank opposite vehicle 1 and that the beam 7 has been moved back relative to vehicle 1 until the three spans are kept on beam 7 by the rear link arm of the rear span 5.

After removal of the front stabilizer jack VA from its inclined position shown in Figures 17 A and B to its approximately vertical position represented in Figure 17C, the beam 7 is tilted by the plate tilting P until the end of the span of great length be deposited on the bank of the breach 2 adjacent to vehicle 1 as shown in the figure 17D. During the tilting of the beam 7, the arm of rear link 5c of span 5 revolves around two OX axes so that the link arm adapts at the different inclinations of the beam 7 and ensures the resumption of the very long span on the beam 7.

Figure 17E shows that the tip or nose of the beam 7 is released from the rear link arm of the span 5 by retraction of the beam 7 on the plate P while FIG. 17F shows that the beam 7 is in position straightened by rotation of the tilting plate P.

Figure 18 shows the situation where one of the banks where the end part rests corresponding to a span, for example span 3, has an uneven height or walks when viewed in cross section. In this case, each arm of link 3c must allow the span to adapt to this bank configuration or any other configuration, such as for example the one where the bank consists of two inclined parts one towards the other. Thus, in service, the significant weight of vehicles moving on the span allows compress the pre-stressed springs 34 associated respectively to cams 27 and the assembly can be deform as shown in figure 18 by displacement along the two axes OZ of the link arm 3c and therefore adapt to different bank configurations. This function optimizes the weight of the arms of bond which are dimensioned by the self weight of the launching bridge and the braking effects of vehicles and not by the efforts exerted on the passage of vehicles.

Of course, the connecting arms of the spans must keep the two span elements parallel and prevent them from shifting relative to each other whatever the external actions exerted on them such as passing vehicles, braking vehicles, cant, etc. For this purpose, efforts are taken up by ball joints 17 and bearings 24 as indicated by the different arrows shown in Figure 7.

The span structure described above of the invention therefore allows each of its link arms to retract in the transport configuration of overlapping spans, to support the moment due to dead weight of the works in the launch phase; of transmit the translational forces of each works relatively to the launching beam and deposit ; to bear the weight of the span at the deposit ; to adapt to the relative angle, when removal, between span and launching beam; of adapt to the different bank conditions and link the two span elements in parallel one compared to each other.

Claims (15)

1. Bridge element especially designed for surmounting gaps (2) by vehicles, such as military engineering armoured machines, comprising two parallel bridge members (3a, 3b ; 4a, 4b ; 5a, 5b) with upper rolling paths (3d ; 4d ; 5d) and connected together by means of two bracing link arms (3c ; 4c ; 5c), characterized in that each link arm (3c ; 4c ; 5c) is approximately in the shape of a Ω the two coaxial bottom members of which are formed by pins (16) each having their ends that are connected to the body (8) of the corresponding bridge member by means of a toggle joint (17) ; each articulated pin (16) being rotatably mounted, at the opposite of its toggle joint (17), in a bearing member (24) that is rotatably immobilized to the body (8) of the bridge member and can slide relatively thereto in order to permit the displacement of the articulated pin (16) in a plane that is perpendicular to the bridge member around the articulation centre (C) of this pin (16) ; and in that means are provided for automatically returning each link arm (3c ; 4c ; 5c) to its normal position of use in a plane that is substantially perpendicular to the two bridge members and maintaining the link arm (3c ; 4c ; 5c) at this normal position of use.
2. Bridge element according to claim 1, characterized in that said means for returning and maintaining each link arm (3c ; 4c ; 5c) comprise two parallel identical cam members (27) that are rigidly connected with the link arm (3c ; 4c ; 5c) respectively at the two ends of the articulated pins (16) that are opposed to the toggle joints (17) and the rotation axes of which are coaxial to the rotation axes of the articulated pins (16) ; two rollers (28) that are bearingly maintained by means of an elastic means (34) onto the lower part of the eccentric shape of each cam member (27) according to an effort maintaining the link arm (3c ; 4c ; 5c) at its normal position of use, the eccentric shape of the cam member (27) being such that, upon rotation of the link arm (3c ; 4c ; 5c) in either direction, either one of the two rollers (28) will exert on this cam member (27) a torque for raising the link arm (3c ; 4c ; 5c) up to its normal position.
3. Bridge element according to claim 2, characterized in that said two rollers (28) are mounted in a common yoke (30) that is rigidly connected with one end of a support pin (31) which is slidably mounted in a fixed casing (32) that is rigidly connected with the body (8) of the corresponding bridge member and in that the elastic means comprises a pre-stressed spring (34) housed in the fixed casing (32) and exerting on the support pin (31) a force for bearingly maintaining the two rollers (28), or one of them, on the periphery of the corresponding cam member (27).
4. Bridge element according to claim 2 or 3, characterized in that the lower part of each cam member, where are simultaneously bearing the two corresponding rollers (28), is a flat part and is situated between two symmetrical portions of the eccentric shape of the cam member (27).
5. Bridge element according to one of the preceding claims, characterized in that said bearing member (24) is a parallelepiped block that is housed in a rectangular window (25) for guiding the block (24) made in the body (8) of the corresponding bridge member perpendicularly to the longitudinal axis thereof.
6. Bridge element according to one of the preceding claims, characterized in that each toggle joint comprises a half round hollow part (18) for supporting the female sphere (19) in which is housed the male sphere (20) that is rigidly connected with the end of the corresponding articulated pin (16), the supporting half round hollow part (18) being itself fixed in a support piece (21) that is rigidly connected, for example by soldering, with the body (8) of the corresponding bridge member.
7. Bridge element according to one of the preceding claims, characterized in that it comprises, operatively associated with each one of the two link arms (3c ; 4c ; 5c), at least two stops (35) that are rigidly connected respectively with the two bridge members and on which can bear the corresponding link arm (3c ; 4c ; 5c) in the turned-down position thereof.
8. Bridge element according to one of the preceding claims, characterized in that each link arm (3c ; 4c ; 5c) comprises, rigidly connected with the linking centre part Ω, two pairs of rolling rollers (39) each extending parallel to the bridge members.
9. Bridge element according to one of claims 5 to 8, characterized in that it comprises rubber protective bellows (26) hermetically closing the passages between the bearing members (24) and the guiding rectangular windows (25).
10. Bridge element according to one of claims 3 to 9, characterized in that each pre-stressed spring (34) is, at its maximum length, at the normal position of an associated link arm (3c ; 4c ; 5c).
11. System for transporting, on a road vehicle (1), such as a truck, at least two superimposed bridge elements (3, 4, 5) on a frame (6) of the vehicle able to be end-to-end assembled, and for placing each one of the bridge elements (3, 4, 5) or of the end-to-end assembled bridge elements above a gap to be surmounted, each bridge element (3, 4, 5) having a construction such as that defined in one of claims 1 to 10, and of the type comprising a supporting and throwing beam (7) for a bridge element (3 ; 4 ; 5) or assembled bridge elements (3, 4, 5) that is movable relatively to the vehicle (1) towards an overhanging position ; means for moving the bridge element or the assembled bridge elements relatively to the beam (7) towards an overhanging position frontwardly to the beam (7) and a plate (P) guidingly supporting the beam (7) and able to rock relatively to the vehicle (1) with the beam (7) for placing the bridge element or the assembled bridge elements, characterized in that, upon placing a bridge element (3 ; 4 ; 5) or assembled bridge elements (3, 4, 5), the end of this bridge element or of these assembled bridge elements which is opposed to that already bearing on the bank of the gap (2) that is opposite to the road vehicle (1), is supported at end of the placing and throwing beam (7) by means of the rear link arm (3c ; 4c ; 5c) of the two bridge members (3a, 3b ; 4a, 4b ; 5a, 5b) of the bridge element (3 ; 4 ; 5) or of the rear bridge element of the assembled bridge elements (3 ; 4 ; 5) during the rocking of the beam (7) up to placing said end of bridge element or of assembled bridge elements on the bank that is adjacent to the road vehicle (1), the link arm (3c, 4c, 5c) bearing on the placing beam (7) being pivotable relatively to the bridge members around articulated pins (7) so that the link arm can be adapted to different slopes of the placing beam (7).
12. System according to claim 11, characterized in that, in the transporting position on the road vehicle (1), the placing and throwing beam (7) is arranged between two superimposed bridge elements (3, 4) and the link arms (4c) of the two bridge members (4a, 4b) of the lower bridge element occupy a position that is turned down under the placing and throwing beam (7) by being in contact therewith through rolling rollers (39) of the link arms (4c).
13. System according to claim 12, characterized in that the two turned down link arms (4c) are also bearing on the stops (35) that are rigidly connected with the bridge members (4a, 4b).
14. System according to claim 12 or 13, characterized in that said link arms (4c) are raised up to their normal position by returning means exerting a raising torque thereupon, after withdrawal of the beam (7) from between the two superimposed bridge elements (3, 4).
15. System according to one of claims 12 to 14, characterized in that the means for moving the bridge element (3 ; 4 ; 5) or the assembled bridge elements (3, 4, 5) relatively to the beam (7) comprise a driving endless chain (40) that is extended according to the longitudinal axis of the beam (7) and is mounted on at least two end toothed wheels (41) that are rotatably mounted on the beam (7) ; and at least two fork forming members (42) that are rigidly connected with the driving chain and able to grip the centre part of a link arm (3c ; 4c ; 5c) between the two pairs of rolling rollers (39) of this arm bearing on the placing and throwing beam (7).

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