EP0461216B1 - Propulsion device for a railway modernization flatcar - Google Patents

Abstract

A propulsion device for a vehicle on rails, particularly a railway modernizing flatcar, of the kind in which movement is obtained by applying the power required for propulsion directly between the vehicle's frame and the rails, thereby bypassing the wheels. The device comprises hinged means (11-14, 31-34) for connecting it to the frame of a railway vehicle, means (1-2) for moving the propulsion device between a non-operational raised position during transit and an operational lowered position, two movable crosspieces (15, 35), means (13, 14, 33, 34) for supporting the movable crosspieces and guiding them along a path which is longitudinal with respect to the frame, hydraulic drive cylinders (16, 36) mounted between each of the two movable crosspieces (15, 35) and the frame, jaws (19, 39) mounted at both ends of each said crosspiece and able to engage the corresponding rails, and actuators (2, 42) arranged to control the engagement of said jaws (19, 39) with the rails, in conditions which make it possible to produce forward or reverse propulsive power.

Description

TECHNICAL AREA

The present invention relates to a propulsion device for a vehicle on rails, and especially for a train set intended to be used for the movement of railway or other machinery. More precisely, the invention relates to a propulsion device of the type in which the movement is obtained by applying the force necessary for the propulsion directly between the chassis of a vehicle and the rails, without intervention of the wheels.

PRIOR ART

Many types of rail vehicles or trains are known to be able to be moved (by their own means or harnessed to other trains) on the railway tracks, to carry them from a depot to a work region. and, this achieved, to execute by mechanical means different operations, such as for example the removal of rails to be replaced, the removal of old sleepers, the cleaning up of the ballast, the laying of new sleepers, the laying of new rails, or even other operations. These trainsets must be fitted with propulsion devices which ensure their regular progress during the execution of the works. The necessary advance is relatively slow, for example of the order of magnitude of 10 meters per minute, but it requires a high propulsion effort, for example of the order of magnitude of 200,000 N, in consideration of the large resistances who oppose advancement during labor. As a result, the usual means of propulsion for railway trains cannot be used with advantage. For this purpose, propulsion devices by continuous hydrostatic transmission can be used, acting on the wheels of oar, but these devices have high installation and exercise costs and give rise to adhesion problems. As an alternative, it is possible to use propulsion devices by hydraulic cylinders operating without the intervention of the wheels by taking hold directly on the rails, but in their known forms these devices have the disadvantage of giving rise to an intermittent advance of the train, which n is not desirable for a regular development of the operations carried out, or else they are not able to produce a retrograde advance, which may be necessary sometimes, even only for limited lengths, but with frequent repetition.

STATEMENT OF THE INVENTION

The object of the present invention is to improve the propulsion devices for rail vehicles of the last type indicated, particularly the propulsion devices for train sets intended for the purposes indicated in principle, so as to ensure at the same time favorable conditions of installation and exercise, continuous and uniform propulsion at a speed that can be adjusted easily and exactly, the availability of the high effort required without introducing adhesion problems, as well as the possibility of reversing the direction of walks without substantially modifying the characteristics of propulsion effort and speed.

The device of. propulsion according to the present invention is characterized in that it comprises articulated means for its connection to the chassis of a railway vehicle, means for moving the propulsion device between a raised neutral position for the transfer operation and a lowered operating position , two movable sleepers, means for supporting said movable sleepers and guiding them independently of one another along a path of longitudinal displacement relative to the chassis of the vehicle, hydraulic traction cylinders connected between each of said movable sleepers and the vehicle chassis, jaws mounted at both ends of each movable cross member, capable of engaging the corresponding rails, and actuation means arranged to activate and deactivate the engagement of the jaws relative to the rails, under conditions capable of producing a propulsion force in a progressive or retrograde direction.

In a particularly intended embodiment, said jaws engage the rails by wedging, and said actuating means act by moving said jaws relative to the movable crosspieces so as to activate or deactivate said engagement by wedging in relation to progressive advancement or else , respectively, retrograde, of the vehicle.

Owing to these characteristics, the propulsion device according to the invention can be raised to a neutralized position for the transfer step, which in this way is not disturbed, and then it can be lowered at the appropriate moment to ensure propulsion. oar during the period in which it is in work. When the propulsion device is in the operative position, the mobile sleepers can be secured alternately to the rails by means of their respective engagement jaws, thus constituting a fixed point of support allowing the hydraulic traction cylinders to transmit to the chassis of the carrier vehicle ( and therefore thus to the whole train of which it is a part) the desired propulsion effort. While a first cross member is thus secured to the rails to provide a fulcrum, the jaws of the second cross member can be disengaged from the rails, and then the second cross member can be moved forward by the corresponding traction cylinders, by bearing in an advanced position, reaching which it can be secured again to the rails to provide a new fulcrum. The first cross member can then be advanced in a similar manner, which in the meantime has moved rearward relative to the vehicle that is being advanced. By providing, in the execution of these operational phases, a certain superposition of the periods of thrust produced by the two sleepers, it is possible to ensure continuous and uniform propulsion of the train. The fact that the propulsion is carried out by hydraulic cylinders ensures the easy obtaining of the high effort required, without introducing adhesion problems, as well as an easy and exact adjustment of the speed of advance printed on the train. The fact that the jaws of the mobile sleepers can be engaged with the rails in conditions such as to produce a propulsion force in the progressive direction or else in the retrograde direction also ensures the possibility of performing reverse steps when necessary, with propulsion characteristics similar to those of progressive walking. Finally, the nature itself of the means employed ensures the economy of the installation and the exercise of the device.

The propulsion device according to the invention can be applied equally to any of the vehicles constituting the operating assembly of the train, or to any of the storage wagons forming part of the train itself. This latter possibility can be shown to be advantageous in view of the large number of other apparatuses which have to find their place on the vehicles of the operational assembly, and it depends on the fact that the adhesion of the device, being generated by an engagement of jaws by relative to the rails, is independent of the weight of the vehicle on which the propulsion device is mounted.

Special provisions may be made to ensure the correct insertion of the mobile sleepers with their jaws in correspondence with the curves of the track, as well as to block the sleepers in their inactive condition.

SUMMARY DESCRIPTION OF THE DRAWINGS

• Fig. 1 montre en vue latérale et à une petite échelle un véhicule ferroviaire equipé avec le dispositif de propulsion suivant l'invention, en position opérative;
• Fig. 2 montre d'une façon similaire le véhicule de la figure 1, mais avec le dispositif de propulsion dans sa position neutralisée de transfèrement;
• Fig. 3 montre à une échelle plus grande et avec plus de détails le dispositif de propulsion suivant la figure 1, séparé du véhicule;
• Fig. 4 montre en vue en plan la partie inférieure du dispositif de propulsion suivant la figure 3;
• Fig. 5 montre à une échelle plus grande un détail, vue de dessous, d'une traverse mobile avec les mâchoires respectives engagées avec le champignon des rails;
• Fig. 6 montre une mâchoire isolée, vue de dessous;
• Fig. 7 montre en élévation les conditions d'engagement d'une mâchoire avec le rail respectif; et
• Figs. 8 et 9 montrent deux exemples différents de réalisation des mâchoires pour l'engagement avec les rails.

The particulars indicated and others as well as the advantages of the object of the invention will emerge more clearly from the following description of an embodiment, given by way of a nonlimiting example, and shown schematically in the accompanying drawings , wherein:

• Fig. 1 shows in side view and on a small scale a railway vehicle equipped with the propulsion device according to the invention, in the operative position;
• Fig. 2 similarly shows the vehicle of FIG. 1, but with the propulsion device in its neutralized transfer position;
• Fig. 3 shows on a larger scale and in more detail the propulsion device according to FIG. 1, separated from the vehicle;
• Fig. 4 shows in plan view the lower part of the propulsion device according to FIG. 3;
• Fig. 5 shows on a larger scale a detail, seen from below, of a movable cross member with the respective jaws engaged with the head of the rails;
• Fig. 6 shows an isolated jaw, seen from below;
• Fig. 7 shows in elevation the conditions of engagement of a jaw with the respective rail; and
• Figs. 8 and 9 show two different examples of construction of the jaws for engagement with the rails.

PREFERRED WAY OF CARRYING OUT THE INVENTION

Referring for example to a train for the renewal of railways, this train generally comprises an operator assembly consisting of one or more wagons, subsequent operator means installed on wagons following the train, and a certain number of storage wagons , intended to carry the new materials to be installed as well as to receive the old materials removed. Any one of these wagons, to which the propulsion function of the train is assigned in this case, is shown in Figures 1 and 2.

The wagon shown in Figures 1 and 2 has a chassis T which, in this case, is supported on wheels R by means of two bogies C. In other cases these bogies could be replaced by simple axles. The chassis T carries a loading platform P on the top, which can optionally be equipped with a service channel for handling materials.

On each side of the wagon, at frame T are articulated, in points 10 and 30, two support arms 11 and 31 which support the propulsion device. The support arms 11 and 31 are provided with lever arms 12 and 32 which, with the support arms, form square levers. Between the lever arms 12 and 32 is installed a hydraulic unit comprising a cylinder 1 and its piston rod 2. By this arrangement, when the hydraulic unit 1-2 is extended, the support arms 11 and 31 are lowered and the propulsion device is in an operative position (Figure 1), with the possibility of engaging the rails B of the track. When, on the contrary, the hydraulic unit 1-2 is contracted, the support arms 11 and 31 are raised (FIG. 2) and the propulsion device is entirely located at a level higher than the level of track B. In this position the propulsion device, inactive, allows free movement of the wagon on the track, for approaching or away from the work area.

On each side of the wagon, on each support arm 11 and 31 is suspended a lever, respectively 13 and 33, which by means of a connecting rod, respectively 14 and 34, supports a movable cross member, respectively front 15 and rear 35 At the lower ends of the levers 13 and 33 are connected the rods of two hydraulic cylinders, respectively 16 and 36, articulated at points, respectively 17 and 37, fixed to the chassis T of the wagon. As can be understood, the actuation of the cylinders 16 makes it possible to move the levers 13, and with them the front cross member 15, between the position moved forward shown in the drawings, and a position 13 'moved backward, shown by lines in dots and lines in FIG. 3. In the same way, the actuation of the hydraulic cylinders 36 makes it possible to move the levers 33, and with them the rear crossmember 35, between the position moved backwards shown in the drawings, and a position 33 'moved to front, shown by dotted and dashed lines in Figure 3.

Between the connecting rods 14 and the levers 13, as well as between the connecting rods 34 and the levers 33, are arranged hydraulic cylinders, respectively 18 and 38, which give the possibility of adjusting the position of the connecting rods relative to the corresponding levers. By appropriate control of the hydraulic cylinders 18 and 38 it is possible to obtain that the cross members 15 and 35, under the effect of the cylinders 16 and 36, move along parallel paths of the rails B, despite the fact that the lower ends of the levers 13 and 33 run through arcs of a circle. In this way it can be ensured that the engagement jaws, described further on and installed at the ends of the movable crosspieces, remain adherent or else in strict proximity to the running surface constituting the upper part of the rails.

At the ends of the mobile sleepers 15 and 35 are articulated jaws, respectively 19 and 39. In the embodiment now described, these jaws are intended to engage the rails by wedging. For this purpose each jaw is provided with a notch, respectively 20 and 40, capable of engaging the head of a rail B (Figures 5 to 7). The jaws 19 and 39 are provided with control arms, respectively 21 and 41, which form with the jaws angled levers. Between the arms 21 of the front jaws 19 is inserted a double hydraulic unit 22 with cylinders and pistons, and between the arms 41 of the rear jaws 39 is similarly inserted a double hydraulic unit 42 with cylinders and pistons. The hydraulic units 22 and 42 allow the jaws 19, respectively 39, to oscillate relative to the movable cross members 15 and 35 to which they belong, as shown in FIG. 5. FIG. 5 refers in particular to the rear movable cross member, but a very similar behavior is achieved for the anterior mobile crossmember.

Referring to Figure 5, when the jaws 39 have been carried by the double hydraulic cylinder 42 in the position indicated by solid lines, their notches 40 engage the fungus of rails B in a position such that a force, applied to the cross member 35 by the hydraulic cylinders 36 in the direction of the arrow F, tends to increase the jamming between the jaws 39 and the rails B. Therefore, in these conditions the action of the hydraulic cylinders 36 cannot move the cross-member 35 relative to the rails B, on the contrary it advances, in the direction opposite to the arrow F, the wagon to the chassis of which the cylinders 36 are articulated. We then realize a progressive advancement of the wagon.

When, on the contrary, the jaws are carried by the double hydraulic cylinder 42 in the position 39 'indicated by lines with dots and lines, there is no wedging between the notches 40 of the jaws 39 and the rails B, therefore the cross member 35 can be freely moved relative to the rails.

When, finally, the jaws 39 have been carried by the double hydraulic cylinder 42 in the position 39 '' indicated by lines with double dots and lines, the notches 40 engage the head of the rails B in a position such as a force, applied to the cross member 35 by the hydraulic cylinders 36 in the direction opposite to the arrow F, tends to increase the wedging between the jaws 39 and the rails B. Therefore, under these conditions, the action of the hydraulic cylinders 36 can not move the cross 35 relative to the rails B, on the contrary it advances, in the same direction of the arrow F, the wagon to the chassis of which the cylinders 36 are articulated. We then carry out a retrograde advancement of the wagon.

To make jamming more secure with respect to the rails B, the notch 40 of the jaw 39 (as well as the notch 20 of the jaw 19) can be provided with regions 40 ′ (FIG. 6) crenellated, knurled or roughened by any other means, or else filled with an adhesive material. In order to be able to adapt to the differences in the spacing of the rails B of the track, the cross-member 35 is preferably provided with a telescopic seal 35 'which allows a limited modification of its length, and a similar arrangement. is taken for the anterior crossmember 15. Finally, preferably, the crosspieces 15 and 35 are connected to each other by a spar constituted by two parts 3 and 4 telescopically coupled to one another, so as to allow independent displacements of the crosspieces in the longitudinal direction. The crosspieces are articulated to said spar 3-4 by pivots 5, arranged so as to allow a limited angular orientation of the mobile crosspieces, for the effect of a correct engagement with respect to the rails B in correspondence of a curvature of the latter. .

The left-hand part of FIG. 5 shows a safety device which can be adopted advantageously. This device comprises a pair of hydraulic units 47 and 48 with cylinder and piston, the rods of which act on a plate 49 secured to the jaw 39. The hydraulic units 47 and 48 are inactive during the propulsion phase, and they are arranged to force the jaw 39 to assume the position 39 ', not engaged with the rail B, when said units are activated. Of course, such units are provided for all the jaws of the propulsion device. Activation of these hydraulic units when the jaws 39 have to be moved along the rails B ensures that the jaws cannot be caught with the rails by accident as a result of disturbances due, for example, to deformations, dents or rail burrs, abnormal friction and so on.

To allow automatic control of the actuation of the device, preferably the latter comprises sensors which detect the arrival of the levers 13 and 33 in particular positions. In more detail, as shown in FIG. 3, in connection with the front levers 13, the following sensors can be provided: 23, which detects the achievement of the end of travel position forward by the front lever 13; 24, which detects the arrival in a position shortly before the end of travel detected by the sensor 23; 25, which detects the achievement of the rear end position by the front lever 13; and 26, which detects the arrival in a position shortly before the end of stroke detected by the sensor 25. In the same way, in connection with the rear levers 33, the following sensors can be provided: 43, which detects the achievement of the end of travel position forward by the rear lever 33; 44, which detects the arrival in a position shortly before the end of travel detected by the sensor 43; 45, which detects the achievement of the rear end position by the rear lever 33; and 46, which detects the arrival in a position shortly before the end of travel detected by the sensor 45.

The actuation of the propulsion device according to the invention can be carried out as follows.

After having completed a stroke of proximity of the train to a working region, this stroke being carried out with the propulsion device raised according to FIG. 2, the propulsion device is lowered according to FIG. 1 by actuating the hydraulic units 1-2 , and by this operation the notches 20 and 40 of the jaws 19 and 39 engage the mushrooms of the corresponding rails B. Supposing to start from the configuration according to FIG. 3, the double hydraulic cylinder 22 is contracted, while the double hydraulic cylinder 42 is brought to an intermediate position. By this the front jaws 19 are engaged with wedging with the rails B, while the rear jaws 39 are not jammed with the rails.

The hydraulic cylinders 16 are then activated in expansion, while the hydraulic cylinders 36 are activated in retraction. Because the jaws 19 are engaged with wedging with the rails B, the traction cylinders 16 produce an advancement of the wagon, during which the levers 13 oscillate towards the position 13 '. This movement is made with the set speed that we want to impose on the advancement of the wagon and the train. At the same time, the cylinders 36 produce an oscillation of the levers 33 towards the position 33 'and the jaws 39, which are not jammed with the rails B, move forward relative to the latter; this movement can be rapid.

When the sensors 43 detect the arrival of the levers 33 in the end position forwards, the action of the cylinders 36 is interrupted. When, afterwards, the sensors 26 detect that the levers 13 are close to arriving at the rear end position, the double cylinder 42 is activated in retraction, thus causing the jaws 39 to jam with the rails, and the cylinders 36 are also activated in retraction, so that they add their action to that of the cylinders 16 for the production of the advancement of the wagon. The phase in which the cylinders 36 as well as the cylinders 16 together control the advance is maintained only for a short period in order to ensure the continuity of the propulsion. As soon as the sensors 25 detect the arrival of the levers 13 in their end-of-travel position back, the activation of the cylinders 16 is reversed and the double cylinder 22 is brought to an intermediate position, so that the propulsion by the cylinders 16 ends, and these cylinders move forward relative to the rails the jaws 19, which are no longer stuck with the rails. The propulsion is now carried out only by the cylinders 36.

When the sensors 23 detect the arrival of the front levers 13 in their end of travel position forward, the cylinders 16 are deactivated. When, afterwards, the sensors 46 detect that the levers 33 are close to arriving at the rear end position, the front cylinders 16 and 22 are again brought into the propulsion condition, as at the beginning of the cycle described, so that they add their action to that of the traction cylinders 36. When finally the sensors 45 detect the arrival of the levers 33 in their rear end position, the activation of the cylinders 36 is reversed and the double cylinder 42 is brought to an intermediate position, so that the repetition of the described cycle begins.

It should be particularly noted that the superimposition, for a certain extension, of the propulsion phases carried out by the traction cylinders 16 and 36, ensures the possibility of obtaining uniform advancement, without any solution of continuity.

It will be clearly understood by those skilled in the art as the cycle described must be modified to achieve retrograde advancement, instead of progressive, of the vehicle. For this purpose the double cylinders 22 and 42 are carried, during the propulsion period, in expansion instead of in retraction, by oscillating the jaws in positions similar to those shown in 39 '' in Figure 5. The superposition periods of propulsion carried out by the front and rear traction cylinders is possible due to the presence of sensors 24 and 44, which are not active during progressive propulsion, while during retrograde propulsion are not active the sensors 26 and 46.

In the embodiment described so far, the jaws of the propulsion device engage the rails by wedging, tilting relative to the crosspieces which carry them. However, it is also possible to provide jaws acting in any other way, in particular by clamping. For example, as shown in FIG. 8, a jaw can comprise a fixed part 59 and a part 61 movable in horizontal direction under the action of a hydraulic unit, of which the piston rod 62 is shown. Such a jaw is capable tighten the sides of the head of a rail B to achieve the desired engagement.

Alternatively, as shown in FIG. 9, a jaw can comprise a fixed part 69 provided with elements 70 arranged (in their operational condition) under the head of the rail B, and a part 71 movable in vertical direction under the action of a hydraulic unit 72. Such a jaw is capable of clamping in the vertical direction the head of a rail B to achieve the desired engagement. Of course, unlike the embodiment according to FIGS. 4 and 5, in embodiments like those shown by way of example in FIGS. 8 and 9 the jaws do not require to be articulated at the ends of the movable crosspieces of so as to be able to oscillate relative to the latter, but on the contrary they can be fixed relative to the crosspieces.

The propulsion device described is simple, relatively economical and extremely reliable, and it makes it possible to obtain, by a minimum consumption of power, the high thrusts necessary, by achieving continuous advancement, whether progressive or retrograde, at a speed uniform, precisely adjustable. The fact that the propulsion device, not having adhesion problems, can be applied to a storage wagon instead of to a wagon of the operating train, in certain cases makes it lighter, simple and economical. renewal train as a whole. However, it is obvious that, when it seems preferable, the propulsion device can also be applied to one of the wagons of the operating train.

Although we discussed a train for the renewal of railways, as it represents the typical case of application of the propulsion device according to the invention, it should be understood that this device can be applied, in general , for the propulsion of any vehicle on rails. It should also be understood that the device according to the invention may include all of the characteristics set out or else only a part of these characteristics, depending on the particular requirements of the applications envisaged. Various modifications may be made to the details described, and all parts and groups may be replaced by their technical equivalents, within the scope of the claims of this patent.

POSSIBILITIES OF INDUSTRIAL APPLICATION

The propulsion device according to the invention can find advantageous applications on any railway vehicle for which relatively slow, uniform advancement is required, under a high tensile force. The most characteristic application is that of propelling a train intended for carrying out work on a railway track.

Claims (15)

1. A propulsion device for a vehicle on rails, and mainly for a railway train intended to be used for the renewal of railway tracks, of the kind in which the movement is obtained by applying the power needed for the propulsion directly between the frame (T) of the vehicle and the rails (B), without intervention of the wheels (R), characterized in that it comprises articulated means (11-14, 32-34) for its connection to the frame (T) of a railway vehicle, means (1-2) for displacing the propulsion device between a lifted neutralized position for the transfer travel and a lowered working position, two movable cross-bars (15,35), means (13-14, 33-34, 3-4) for supporting said movable cross-bars and for guiding them independently the one from the other along a displacement trajectory longitudinal with respect to the vehicle frame (T), traction hydraulic cylinders (16,36) connected between each said movable cross-bar (15,35) and the vehicle frame (T), jaws (19,39; 59; 69) mounted at both ends of each movable cross-bar, suitable for engaging the corresponding rails (B), and actuation means (22,42; 62; 72) provided for making active or inactive the engagement of the jaws with respect to the rails, in such a way that a propulsion force is produced, in the progressive or the regressive direction.
2. A propulsion device as set forth in Claim 1, characterized in that said articulated means (11-14, 32-34) for connection to the frame (T) and said means (1-2) for displacing the propulsion device between a neutralized position and a working position comprise a pair of supporting arms (11,31) articulated to points (10,30) fixed to the frame (T) and having square lever arms (12,32), and a hydraulic unit (1-2) comprising a cylinder (1) and a piston (2), connected to said lever arms (12,32); some levers (13,33) being part of the propulsion device hanging from the outer ends of said supporting arms (11.31).
3. A propulsion device as set forth in Claim 1, characterized in that said means for supporting and guiding the movable cross-bars include suspension levers (13,33), at whose bottom ends said traction hydraulic cylinders (16,36) are connected.
4. A propulsion device as set forth in Claim 3, characterized in that said means for supporting and guiding the movable cross-bars also include connecting rods (14,34) interposed between the bottom ends of the suspension levers (13,33) and the cross-bars (15,35), and hydraulic cylinders (18,38) provided for correcting, by means of said connecting rods (14,34), the trajectory followed by the movable cross-bars (15,35) in their displacement.
5. A propulsion device as set forth in Claim 1, characterized in that said movable cross-bars (15,35) have a telescopic structure for the adaptation to the gauge modifications of the way.
6. A propulsion device as set forth in Claim 1, characterized in that said cross-bars (15,35) are connected the one another by a telescopic longitudinal bar (3-4) to which the movable cross-bars are pivoted.
7. A propulsion device as set forth in Claim 1, characterized in that said jaws (19,39) engage the rails (B) by wedging, and said actuation means (22,42) operate by displacing said jaws with respect to the movable cross-bars (15,35) in such a way that said wedging engagement is made active or inactive with respect to a progressive or respectively a regressive displacement of the vehicle.
8. A propulsion device as set forth in Claim 7, characterized in that said jaws (19,39) are pivoted on the ends of the respective cross-bars (15,35) in such a way that they may oscillate both forward and rearward with respect to a position of non-engagement which is substantially aligned with the corresponding movable cross-bar, and that each jaw (19,39) has a recess (20,40) capable of engaging the head of a rail (B), it being free to slide when the jaw is in the position aligned with the cross-bar, and wedging with the rail when the jaw assumes an inclined position.
9. A propulsion device as set forth in Claim 8, characterized in that said means (22,42) for actuating the jaws (19,39) comprise hydraulic units capable of expanding and contracting, said units connecting the one another actuating levers (21,41) shown by the jaws (19,39) mounted on the opposite ends of the same movable cross-bar (15,35).
10. A propulsion device as set forth in Claim 8, characterized in that it includes means, such as hydraulic units (47,48), provided for blocking said jaws (19,39) in the non-wedging condition, against accidental actions tending to cause a untimely wedging.
11. A propulsion device as set forth in Claim 1, characterized in that said jaws (19,39) have in their active portions some regions (40') which are furrowed, knurled, roughened, provided with a friction material, or otherwise contidioned for favouring the wedging with respect to the rails.
12. A propulsion device as set forth in Claim 1, characterized in that said jaws (59; 69) engage the rails (B) by grasping, and that said actuation means (62; 72) act by displacing movable parts (61; 71) of the jaws (59; 69) with respect to their fixed parts.
13. A propulsion device as set forth in Claim 1, characterized in that, to the purpose of an automatic actuation, it includes sensors (23, 25,43,45) arranged for detecting reaching the position of front and back end of stroke by certain elements (13,33) of the propulsion device which are connected to the movable cross-bars (15,35).
14. A propulsion device as set forth in Claim 13, characterized in that it further includes sensors (24,26,44,46) arranged for detecting reaching a position near the end of stroke by said elements (13,33) of the propulsion device.
15. A propulsion device as set forth in Claim 13, characterized in that said elements of the propulsion device which are controlled by the sensors (23-26, 43-46) are suspension levers (13,33) which sustain the movable cross-bars (15,35).

Images