Patent Publication Number: US-2023142608-A1

Title: Tamping machine, rail works train and method for operating such a train

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates in particular to works for laying, maintaining or repairing a rail track. It relates more specifically to operations referred to as tamping, which consist in having tamping tools penetrate the ballast in the gap between the sleepers of the rail track, in order to mechanically compact the ballast under the sleepers. 
     PRIOR ART 
     The tamping machines are typically integrated in works trains, which comprises a plurality of cars that are coupled to one another, in order to perform successive operations required for laying, repairing or replacing the rail track. A works train of this kind is capable of advancing continuously, at a low speed, on the rail track, without stopping, and preferably at a constant work speed, each train machine having to provide its own functions at this work speed. The tamping operation, in turn, requires the part of the tamping machine which supports the tamping tools to remain stationary with respect to the rail track, for the time necessary for the tamping tools to penetrate into the ballast between two successive sleepers of the track, for the generation of a vibratory movement of the tamping tools in the ballast, and then for the retraction of the tamping tools from the ballast. 
     In order to reconcile these conflicting requirements, architectures of tamping machines are known, illustrated for example by the documents FR2476708 and FR2556752, in which the tamping machine comprises a machine frame that is borne by two trucks arranged at the ends thereof, and a tamping shuttle comprising a shuttle frame that is suspended from the machine frame and guided longitudinally in translation with respect to the machine frame, by slides, between two end-of-travel positions, the shuttle frame bearing tamping tools that are movable perpendicularly to the plane of the rail track. The machine frame is intended to be coupled to other cars of a works train and to advance at a constant work speed, on the rail track. During a tamping cycle, the tamping shuttle moves with respect to the machine frame, in the direction opposed to the advancement direction of the machine train, from an initial position, at a speed that is equal in absolute value to the advancement speed, so as to remain immobile with respect to the track during the phase of penetration of the tools into the ballast, of generation of the vibratory movement of the tools in the ballast, then of retraction of the tamping tools out of the ballast. Then, once the tamping tools are retracted, the shuttle frame returns towards its initial position in order to start a new cycle under the following sleeper of the track. In the case of a machine of this type, the slides for longitudinal guidance of the shuttle frame with respect to the machine frame must allow a longitudinal relative movement between the two trucks, while withstanding the stresses in reaction to the stresses of penetration of the tamping tools into the ballast, in a vertical direction perpendicular to the longitudinal movement direction of the shuttle frame. The stresses applied to the guide slides thus vary significantly during the operating cycles, which can bring about rapid wear of the slides. 
     According to a variant shown in document FR2 550 808, the machine frame is still borne by two end trucks, but no longer bears the shuttle frame in its entirety, which is borne by mounts on two additional bearing trucks which travel on the rail track and are equipped, if applicable, with braking and drive structure. The only connection remaining between the two frames and a jack acting longitudinally in order to allow the alternate movement of the shuttle frame with respect to the machine frame. In the case of such a machine comprising four trucks, it is the weight of the shuttle frame which alone balances the stress of penetration of the tamping tools into the ballast, without taking advantage of the weight of the machine frame. The high number of trucks renders this design complex and expensive. 
     DISCLOSURE OF THE INVENTION 
     The invention aims to overcome the disadvantages of the prior art and to propose an alternative tamping machine architecture which allows for a continuous advancement, preferably without stopping, of the tamping machine, while ensuring a step-by-step advancement of the tamping shuttle which bears the tamping tools. 
     In order to achieve this, according to a first aspect of the invention a tamping machine for a works train for laying, repairing or replacing a rail track is proposed, the tamping machine comprising a first truck and a second truck that are located longitudinally at a distance from one another and are intended for supporting the tamping machine, a machine frame and a tamping shuttle, the tamping shuttle having a shuttle frame and one or more tamping units that are vertically movable with respect to the shuttle frame, the shuttle frame being linked to the machine frame by longitudinal guide structure that allow a relative back-and-forth movement, between two end-of-travel positions, between the shuttle frame and the machine frame in a longitudinal direction of the tamping machine, characterized in that the machine frame is entirely supported by the shuttle frame which is borne by the first truck and the second truck. Thus, a tamping machine is achieved having a limited number of trucks, and the longitudinal guide structure of which are subjected to vertical stresses which do not vary over the course of the operating cycles of the machine, since these stresses are only those resulting from the weight of the machine frame and the elements which said frame bears. 
     According to one embodiment, the longitudinal guide structure comprise a first longitudinal rolling interface that is closer to the first truck than to the second truck, and a second longitudinal rolling interface that is closer to the second truck than to the first. Preferably, the first rolling interface and the second rolling interface each comprise at least one longitudinal raceway and at least one associated roller which is capable of rolling on the raceway in order to allow for the back-and-forth relative movement between the shuttle frame and the machine frame, the longitudinal raceway being rigidly connected to one of the two subassemblies formed by the machine frame and the shuttle frame, the associated roller being either translationally secured to the other of the subassemblies formed by the machine frame and the shuttle frame, or guided so as to roll simultaneously on the longitudinal raceway and an opposing longitudinal raceway that is rigidly connected to the other of the subassemblies formed by the machine frame and the shuttle frame. 
     Preferably, the longitudinal raceway of each of the first and second rolling interfaces is rigidly connected to the machine frame, and the associated roller is mounted so as to rotate about a horizontal axis of rotation that is fixed with respect to the shuttle frame, and located longitudinally between at least one wheel set of the first truck and one wheel set of the second truck. For the purpose of a good balance of stresses, the machine frame has a center of gravity that is located between the first rolling interface and the second rolling interface. 
     In a more general manner, the weights are preferably distributed such that, in a median relative position of the machine frame and of the shuttle frame, halfway between the two end-of-travel positions, stopped on a horizontal rail track, each of the first and second trucks supports at least 40% and at most 60% of the total weight of the tamping machine. 
     Outside of the work phases themselves, it may be necessary for the machine to travel on a rail track at a travel speed that is substantially higher than the work speed. For this purpose, it is possible to provide a longitudinal locking device which is capable of rigidly connecting the machine frame to the shuttle frame in a position referred to as the travel position, the locking device comprising at least one lock which is capable of withstanding a critical load exceeding 500 kN, preferably 900 kN, and even more preferably 1500 kN, in the longitudinal direction. The critical load will correspond for example to a sudden stop of the machine frame encountering an obstacle. 
     According to one embodiment, the tamping machine comprises at least one assistance actuator, preferably comprising one or more hydraulic jacks, connecting the machine frame to the shuttle frame, capable of performing one or more of the following operations: 
     blocking the shuttle frame with respect to the machine frame in any intermediate position between the two end-of-travel positions; 
     driving the shuttle frame with respect to the machine frame in a longitudinal direction of the tamping machine, in a back-and-forth movement between the two end-of-travel positions. 
     The function of blocking by the assistance actuator will be implemented in particular at very low speed when, during a work sequence, the tamping machine must pass an item of track equipment, for example points. 
     According to one embodiment, the end-of-travel positions are at least 1 meter, preferably at least 1.5 meters, apart from one another. 
     According to one embodiment, the first truck is guided in rotation with respect to the shuttle frame so as to pivot at least about a first vertical pivot axis, the second truck is guided in rotation with respect to the shuttle frame so as to pivot at least about a second vertical pivot axis, the second vertical pivot axis preferably being located at a distance (D) from the first vertical pivot axis that is greater than 10 meters, preferably greater than 12 meters. 
     It is advantageous for the trucks of the tamping machine to ensure suspension of the tamping machine in the movement phases of the tamping machine at a speed higher than the work speed. In contrast, in the work phases, it is advantageous to eliminate the suspension so as to achieve a high degree of positioning accuracy of the tamping tools between the sleepers. For this purpose, and according to a preferred embodiment, it is provided for the first truck and the second truck to each comprise a truck frame, at least two wheel sets, a primary suspension between the wheel sets and the truck frame. Preferably, the primary suspension of each of the first and second trucks comprises a blocking mechanism that is capable of vertically blocking each of the wheel sets with respect to the truck frame, at least in a bearing direction of the truck frame on each of the wheel sets. Preferably, at least one reference truck from the first and second trucks comprises a rotational locking mechanism that is capable of securing the truck frame of the reference truck with respect to the shuttle frame. 
     According to various embodiments: 
     the machine frame comprises a coupling for connection to an adjacent car of the works train; 
     at least one longitudinal end of the machine frame is equipped with one or more shock pads; 
     the tamping shuttle is entirely located between two opposing longitudinal ends of the machine frame, at least in a median relative position of the machine frame and of the tamping shuttle, halfway between the two end-of-travel positions, and preferably in the two end-of-travel positions; 
     the machine frame comprises a driver&#39;s cab or a control station. 
     According to a preferred embodiment, at least one truck from the first truck and the second truck is a motorized truck comprising at least one motorized wheel set. Preferably, each motorized truck comprises two motorized wheel sets, each driven by a traction motor, preferably a hydraulic motor. The two trucks are preferably motorized trucks. The motorized trucks can in particular be used in the work phases, if applicable in addition to the actuator described above, in order to perform the mechanical work necessary for the relative movement between the shuttle frame and the machine frame. They can also be used also in the movement phases of the tamping machine, at a speed higher than the work speed, preferably after having locked the machine frame in position with respect to the shuttle frame. Preferably, at least one truck from the first truck and the second truck is equipped with a break, a motorized truck comprising at least one motorized wheel set that is driven by at least one motor. 
     According to another aspect of the invention, this relates to a rail works train comprising a tamping machine as described above, and at least one additional car comprising an additional frame coupled to the machine frame of the tamping machine, and at least one additional truck for supporting the additional frame. 
     According to another aspect of the invention, this relates to a method for operating a works train as defined above on a rail track, method according to which, in a work mode, the machine frame is pulled or pushed by the additional frame of the additional car, on the rail track, in a work direction, preferably without stopping, preferably at a constant speed, the shuttle frame moving longitudinally back-and-forth with respect to the machine frame, so as to have stopping phases, with respect to the rail track, during which the tamping units penetrate the ballast of the rail track, and movement phases in the work direction. Preferably, it is ensured that, in the work mode, the tamping shuttle is driven by one or more motorized trucks from the first and the second truck, and/or by one or more assistance actuators connecting the machine frame to the shuttle frame. Preferably, the method also has a movement mode, in which the machine frame is locked in position longitudinally with respect to the shuttle frame. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Other features and advantages of the invention will become clear from the following description, given with reference to the accompanying drawings and explained below. 
         FIG.  1    is a side view of part of a train comprising the work machine and at least one additional car, according to one embodiment of the invention, the work machine comprising a machine frame and a work shuttle in a first end-of-travel position. 
         FIG.  2    is a side view of the train of  FIG.  1   , the work shuttle being in a second end-of-travel position. 
         FIG.  3    is an exploded view of the work machine of the train of  FIG.  1   . 
         FIG.  4    is a schematic view of a first truck supporting the shuttle frame of the work machine of  FIG.  3   . 
         FIG.  5    is a schematic view of a second truck supporting the shuttle frame of the work machine of  FIG.  3   . 
         FIG.  6    is a schematic plan view of the two trucks of  FIGS.  4  and  5   . 
         FIG.  7    is a cross-sectional view in a cutting plane VII-VII of  FIG.  1   , making it possible to see a first rolling interface as well as a first locking device between the machine frame and the shuttle frame. 
         FIG.  8    is an isometric view of the cross section of  FIG.  7   . 
         FIG.  9    is a cross-sectional view in a cutting plane IX-IX of  FIG.  1   , making it possible to see a first rolling interface as well as a first locking device between the machine frame and the shuttle frame. 
         FIG.  10    is an isometric view of the cross section of  FIG.  7   . 
         FIG.  11    is a detailed view of an alternative rolling interface between a machine frame and a shuttle frame of the tamping machine of  FIG.  3   . 
     
    
    
     For reasons of improved clarity, the identical or similar elements are indicated by identical reference signs in all the figures. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS.  1  and  2    show a rail works train  10  for maintaining or repairing a rail track  12 , said train comprising a plurality of rail cars that are coupled to one another, i.e. in this case a work train  14  which in this case is a tamping machine, and at least one additional car  16 , for example a compacting machine that is located behind the work machine  14 , in a direction referred to as the travel direction  100 , on the rail track  12 . 
     The work machine  14 , shown in an exploded view in  FIG.  3   , comprises a work shuttle  18 , in this case more specifically a tamping shuttle, borne by a first truck  20  and a second truck  22  located longitudinally at a distance from one another, as well as a machine frame  24  borne by the work shuttle  18 . 
     The machine frame  24  comprises a longitudinal recess  25  for accommodating the work shuttle  18 , said longitudinal recess  25  being spanned by a longitudinal bridge  125  having a small cross section that constitutes a median portion of the machine frame  24  and connects two opposing longitudinal end portions  126 ,  128  having a larger transverse cross section. The front  126  and rear  128  end portions of the machine frame  24  can be equipped with equipment for interfacing with outer rail vehicles or with track equipment, for example shock pads  26  at the front end  126  and a coupling  28  for connection to the additional car  16  at the rear end  128 . As shown in the figure, the additional car  16  comprises an additional frame  30  coupled to the machine frame  24  of the tamping machine  14  and supported in a manner independent of the work machine  12 , by at least one additional truck  32 . The machine frame  24  is able to support various items of equipment, such as a driver&#39;s cab  34  and a control station  36 , as well as, if applicable, a hydraulic unit  37  which can comprise, for example, a hydraulic pump for supplying various hydraulic motors located in particular on the work shuttle  18 . 
     The work shuttle  18  comprises a shuttle frame  38  which is borne by the first truck  20  and the second truck  22 , as well as one or more work units  40 , in this case tamping units, which are suspended on the shuttle frame  38  and are movable with respect to the shuttle frame  38  in a direction perpendicular to the plane defined by the rails of the rail track  12  (i.e. a vertical direction when the work machine  14  is moving on a horizontal rail track  12 ). The first truck  20  is guided in rotation with respect to the shuttle frame  38  so as to pivot at least about a first vertical pivot axis  120 , the second truck  22  is guided in rotation with respect to the shuttle frame so as to pivot at least about a second vertical pivot axis  122 , the second vertical pivot axis  122  preferably being located at a distance D from the first vertical pivot axis  120  that is greater than 10 meters, preferably greater than 12 meters. 
     The first truck  20 , illustrated in detail in  FIG.  4   , and the second truck  22 , illustrated in  FIG.  5   , each comprise a truck frame  42 , two motorized wheel sets  44  and a primary suspension  46  between the wheel sets  44  and the truck frame  42 . The wheel sets  44  are provided with service brakes  48 . The primary suspensions  46  of the first truck  20  and of the second truck  22  preferably comprise a blocking mechanism  50  which is capable of vertically blocking each of the wheel sets  44  with respect to the truck frame  42  in at least the downward bearing direction of the truck frame  42  on each of the wheel sets  44 . Said blocking mechanism  50  may be made up of hydraulic jacks, the piston of which is rigidly connected for example to the axle box, and the cylinder is rigidly connected to the truck frame  42 . The two truck frames  42  are connected to the shuttle frame  38  via a center plate  142 . 
     Furthermore, at least one of the two trucks  20 ,  22 , for example the first truck  20 , which is intended to be positioned in front of the machine when this advances in the work direction  100  on the rail track  12 , can be equipped with a vertical blocking device  52  for preventing a vertical relative movement between the truck  20  and the shuttle frame  38 . Said device  50  may comprise two retractable lateral support jacks  54  which may be guided hydraulically so as to pass from a retracted position into an operational position in which they constitute two lateral supports between the shuttle frame  38  and the truck frame  42 , thus rigidly connecting the truck frame  42  to the shuttle frame  38 , in the vertical direction, as shown in  FIG.  6   , while the rear part of the shuttle frame  38  rests on axle bars  55  with which the truck frame  42  of the second truck  22  is equipped. The shuttle frame  38  can thus retain its horizontal orientation on a horizontal track, or retain a controlled predetermined angle on a sloping track. 
     The shuttle frame  38  is linked to the machine frame  24  by longitudinal guide structure that allow a relative back-and-forth movement, between two end-of-travel positions, between the work shuttle  18  and the machine frame  24  in a longitudinal direction of the work machine  14 , while preventing vertical and lateral movements. Said longitudinal guide structure comprise a first longitudinal rolling interface  56  that is closer to the first truck  20  than to the second truck  22 , and a second longitudinal rolling interface  58  that is closer to the second truck  22  than to the first  20 , as shown in  FIGS.  3  and  7  to  10   . 
     The first rolling interface  56 , illustrated in detail in  FIGS.  7  and  8   , and the second rolling interface  58 , illustrated in detail in  FIGS.  9  and  10   , each comprise at least one longitudinal raceway  60  and, in this case, each comprise two parallel horizontal longitudinal raceways  60 , two parallel vertical longitudinal raceways  61 , and at least one roller  62 ,  63  associated with each longitudinal raceway  60 ,  61 , the roller  62 ,  63  being capable of rolling on the associated raceway  60 ,  61  in order to allow for the back-and-forth relative movement between the shuttle frame  38  and the machine frame  24 , the longitudinal raceway  60 ,  61  being rigidly connected to one of the two subassemblies formed by the machine frame  24  and the shuttle frame  38 , in this case the machine frame  24 , while the associated roller  62 ,  63  is translationally secured to the other of the subassemblies, i.e. the shuttle frame  38 . 
     In a variant, shown in  FIG.  11   , it is possible to provide one or more rollers  62 ,  63  which roll simultaneously on a longitudinal raceway  60 ,  61  that is rigidly connected to the machine frame  24  and an opposing longitudinal raceway  160  which is rigidly connected to the shuttle frame  38 . 
     The weight of the body of the machine, constituted by the machine frame  24  and the machine elements which it bears, is transmitted integrally to the shuttle frame  38  by the two rolling interfaces  56 ,  58 , which are located on either side of the center of gravity of the body of the machine, such that, when stopped on a horizontal rail track, a load distribution ratio between the first rolling interface  56  and the second rolling interface  58  is between 60% and 140% for every relative position of the machine frame  24  and of the work shuttle  18  between the two end-of-travel positions. Furthermore, the load distribution on the work shuttle  18  and the machine frame  24  is such that, in a median relative position of the machine frame  24  and of the shuttle frame  18 , halfway between the two end-of-travel positions, stopped on a horizontal rail track, each of the trucks  20 ,  22  supports at least 40% and at most 60% of the total weight of the work machine  14 . 
     The work machine  14  is provided with a longitudinal locking device which is capable of rigidly connecting the machine frame to the shuttle frame in a position referred to as the travel position. Said locking device comprises at least two locks  66 ,  68 , which are each located close to a longitudinal end of the shuttle frame  38  and one of the rolling interfaces  56 ,  58 , as shown in particular in  FIGS.  7  and  8   . The lock  66  comprises a bolt  70  which is mounted on one of the two subassemblies formed by the machine frame  24  and the shuttle frame  38 , in this case the shuttle frame  38 , and a striker plate  72  which is mounted on the other of the two subassemblies, in this example the machine frame  24 . The bolt  70  is movable with respect to the subassembly on which it is mounted, between a retracted position and a locking position, and is connected to an actuator  74 , formed in this case by a hydraulic jack. In a similar manner, it can be seen that the lock  68  shown in  FIGS.  9  and  10    comprises a bolt  70  which is mounted on one of the two subassemblies formed by the machine frame  24  and the shuttle frame  38 , in this case the machine frame  24 , and a striker plate  72  which is mounted on the other of the two subassemblies, in this example the shuttle frame  38 . The bolt  70  is movable with respect to the subassembly on which it is mounted, between a retracted position and a locking position, and is connected to an actuator  74 , formed in this case by two parallel hydraulic jacks. 
     When the machine frame  24  is positioned in the travel position, with respect to the shuttle frame  38 , the bolts  70  of the locks  66 ,  68 , passing from their retracted position into their locking position, penetrate the striker plates  72  and achieve the desired rigid connection, respectively between the front  124  longitudinal end portion of the machine frame  24  and the shuttle frame  38 , and between the rear  126  longitudinal end portion of the machine frame  24  and the shuttle frame  38 . The shuttle frame  38  and the machine frame  24  thus form a structural entity, such that some of the stresses exerted on the shock pads  26 , or more generally the interface at the end  126  of the machine frame  24 , is transmitted to the coupling  28 , or more generally to the interface at the end  128  of the machine frame, passing via the locks  66 ,  68  and the shuttle frame  38 , relieving the bridge  125  of the machine frame  24  accordingly. 
     The work machine  14  is preferably equipped with at least one assistance actuator  82  which connects the machine frame  24  to the shuttle frame  38  and has a course of travel that corresponds to the relative course of travel between the shuttle frame  38  and the machine frame  24 , between the two end-of-travel positions. Said assistance actuator  82  may be formed by a hydraulic jack, preferably a jack having two chambers. A jack of this kind makes it possible, by isolating each of the chambers, to block the machine frame  24  with respect to the shuttle frame  38 , in any intermediate position between the two end-of-travel positions. It also makes it possible to drive the machine frame  24  with respect to the shuttle frame  38  in a back-and-forth movement between the two end-of-travel positions. In a variant, it is possible to provide an actuator that is formed of two hydraulic jacks that are arranged in opposition, each of the jacks managing the blocking in one direction and the movement in the opposite direction. 
     The work units  40  borne by the shuttle frame comprise picks  84  mounted on a common frame  86  that is guided so as to move vertically with respect to the shuttle frame, between a retracted position, vertically remote from the rail track, and a work position, plunging into the ballast between two adjacent sleepers  88  of the rail track  12 . Said picks  84  are motorized so as to be able to vibrate about an average position when they are plunged into the ballast, in order to perform the work operation. However, it is only provided for the frame  86  of the work units  40  to be movable longitudinally with respect to the shuttle frame  38 . 
     If applicable, the work machine  14  and the additional car  16  can be provided so as to function in tandem, for example if it is provided for the additional car  16  to bear a motor group for supplying hydraulic power to the hydraulic drive motors mounted on the trucks  20 ,  22 , or the work units  40 . 
     The work machine  14  functions in the following manner. 
     In a mode of operation which can be referred to as the work mode, the train  10  advances at a constant work speed, in a predetermined work direction  100 , for example towards the left in  FIG.  1   . Said constant speed is in particular that of the additional car coupled to the work machine, and is thus also that of the machine frame  24 . In practice it is very low, by way of example less than 5 km/hour. 
     In the work mode, the machine frame  24  is pushed by the frame of the additional car  16  located directly behind the work machine  14 , or pulled by an additional car located directly in front of the work machine  14 , and thus advances at the work speed, in the work direction  100 . The work units  40  must, in turn, alternate stationary phases with respect to the track, in order to allow for penetration of the picks  84  into the ballast and the tamping operation, and rapid advance phases. During the stationary phases, the trucks  20 ,  22  are stationary and the shuttle frame  38 , stopped with respect to the rail track  12 , progressively moves backwards with respect to the machine frame  24 , towards the rear end-of-travel position. During the rapid advance phases, the work units  40  are at a distance from the track, and the shuttle frame  38  accelerates rapidly from the stopped position thereof in the work direction  100 , in order to reach a speed higher than the work speed, and to progress forwards with respect to the machine frame and with respect to the track, before decelerating rapidly to a stop, so as to position the work units  40  above the portion of the rail track  12  directly adjacent to the portion already treated. The driving of the shuttle frame  38  can be performed by hydraulic motors for driving motorized wheel sets  44  of the trucks  20 ,  22 , if applicable assisted by the hydraulic jack  82 . The decelerations can also be obtained by the hydraulic motors which are driven so as to function as pumps in the case of reversible hydraulic machines, or by the service brakes  48 , or by the hydraulic assistance jack  82 , or by a combination of these different structure. 
     The course of travel which the shuttle frame  38  has to cover with respect to the machine frame  24 , at each rapid advance phase, in the work direction, is substantially equal to the course of travel covered by the machine frame  24  with respect to the rail track  12 , in the work direction  100 , during the stationary phase, and thus to the product of the work speed and the stopped time of the shuttle frame  38  with respect to the rail track  12  in the stationary phase. These courses of travel must of course remain within the space delimited by the end-of-travel positions. In practice, the end-of-travel positions are at least 1 meter, preferably at least 1.5 meters, apart from one another. 
     In the work mode, it is advantageously possible to operate the blocking mechanism  50  of the primary suspensions of the two trucks  20 ,  22 , in order to rigidify the trucks  20 ,  22 . It is also possible to operate the device  52  for vertical blocking of one of the trucks  20  with respect to the shuttle frame  38 , for more accurate control of the position of the shuttle frame  38  with respect to the rail track  12 , in all spatial directions. Ideally, the blocking device is actuated intermittently, only when the trucks  20 ,  22  are stopped, and is released when the shuttle advances towards its next work position. 
     It goes without saying that, in the work operating mode, the longitudinal locking device  66 ,  68  is not engaged. If it proves necessary, on a construction site, to interrupt the work mode over some meters, for example for the passage of an item of track equipment, such as points, it is possible to use the hydraulic assistance jack  82  as an additional longitudinal locking device. 
     When they are not in work mode, the work machine  14  and the train  10  are able to travel on the rail track  12  at a speed significantly higher than the work speed, for example at more than 10 km/hour, in order for example to travel to or leave a construction site. In order to allow for a movement of this kind, the blocking mechanism  50  of the primary suspensions  46 , as well as the rotational locking device  54  of one of the trucks, are released, and the machine frame  24  is rigidly connected to the shuttle frame  38  in the travel position, by structure of the longitudinal locking device  66 ,  68 . 
     In practice, the machine frame  24  is positioned, with respect to the shuttle frame  38 , precisely in the travel position, by structure of the hydraulic assistance jack  82 , or the motorized trucks  20 ,  22 , and then one of the locking devices  66 ,  68  is engaged. Very slight structural play is retained between the bolt and the striker plate, in order to make it possible, if applicable after very slight position adjustment by structure of the hydraulic assistance jack  82 , or motorized trucks  20 ,  22 , to engage the other locking device. 
     The locks  66 ,  68  of the longitudinal locking device are dimensioned so as to withstand significant stresses corresponding to a sudden stop of the machine frame  24  when the pads  26  collide with an obstacle when the train  10  is moving at a movement speed that is higher than the work speed. In practice, each of said locks  66 ,  68  is capable of withstanding a critical load exceeding 500 kN (or if applicable exceeding 900 kN, and preferably exceeding 1500 kN) in the longitudinal direction. Thus, the locks  66 ,  68  of the longitudinal locking device make it possible to transmit at least some of the buffering stresses longitudinally from the pads  26  to the coupling  28 , passing via the locks  66 ,  68  and the shuttle frame  38 . It is thus possible to accept relatively lightweight dimensioning of the machine frame  24  in the thinner part  125  thereof, because the machine frame  24  does not have to transfer all the buffering stresses. 
     Of course, the examples shown in the drawings and discussed above are given merely by way of example and are non-limiting. It is explicitly provided that it is possible to combine the different embodiments shown with one another, in order to suggest others. 
     It is emphasized that all the features, as they follow for a person skilled in the art from the present description, the drawings, and the accompanying claims, even if they have been specifically described only in relation with other specific features, both individually and in any combination, can be combined with other features or groups of features disclosed herein, provided that this is not explicitly excluded or that technical circumstances render such combinations impossible or meaningless.