Railroad track relaying train

A railroad track relaying train has, in addition to the cars for transporting the ballast screening machines and a car equipped with power-wrenches for fixing the tie-screws, a sequence of working cars including a tie-and rail-removing car, a ballast clearing car, and a tie and rail laying car. These cars have bogie trucks at both ends and are interconnected by means of coupling frames adapted to bear the adjacent ends of the working cars in the trackless working area and supported by caterpillar trucks adapted to keep the working cars on the selected path, when moving on the ballast cleared track bed. Each caterpillar truck is provided with hydraulic cylinders for raising and lowering the coupling frame relative to the respective truck and with mechanisms for driving and steering the truck.

FIELD OF THE INVENTION 
This invention relates to a railroad track relaying train which, in 
addition to cars for transporting rails, ties and their fastening means, 
comprises at least one sequence of working cars including a track removing 
car, a ballast-clearing car, a track-relaying car, a tie-screw fixing car 
and means for transporting the old ballast to a screener installed on a 
car outside the track-laying area, together with means for transporting 
the screened ballast to a storage and dispensing bin, preliminary to its 
distribution on the new track, and other means for transporting the old 
ties or track panels or spans and the new ties. 
Conventionally, a railroad track relaying procedure comprises not only the 
substitution of new rails and ties for the old ones but also the 
reclaiming of the ballast, since the old ballast, soiled with dirt and 
refuse, is clogged and has lost the necessary elasticity and perviousness. 
On the other hand, the successive additions of gravel during the tie 
truing and ballast tamping operations are attended by an increment in the 
track height, and this may prove rather detrimental on railroad sections 
passing under fixed structures and constructions. 
THE PRIOR ART 
Nowadays, the ballast is normally cleared and screened before or after 
laying the new track. Therefore, the time necessary for this specific 
operation adds itself to the time required for performing the other track 
relaying operations. On the other hand, this ballast clearing and 
screening operation cannot be accomplished without resorting to powerful 
means for lifting the complete track, and this step is obviously attended 
by the risk of altering the shape of the new rails. Now since ballast 
clearing and screening machines have extremely large dimensions, putting 
these machine into operation involves time-robbing and complicated 
maneuvers both when starting and stopping their operation. 
The Applicants are also the owner of the U.S. Pat. No. 4,004,524 disclosing 
a method for the complete relaying of a railroad track, wherein the 
operations consisting in removing the old track, clearing and screening 
the ballast and laying the new track are accomplished during a single 
passage of the complete track relaying train provided for this purpose. 
The same patent also describes a train for the complete relaying of a 
railroad track, which comprises cars for transporting the rails, ties and 
their fixation means, as well as a sequence of working cars provided with 
gantries for removing and laying railroad tracks, and two frame-cars, as 
described in Swiss Pat. Nos. 549,692 and 585,814 also owned by the 
Applicants. The equipment of this known track relaying train comprise 
inter alia means for clearing the ballast and transporting same to a 
screener mounted on a car located outside the track relaying area. The 
frame-cars are interconnected by an intermediate bogie-truck supported by 
a caterpillar chassis and provided with retractable wheels for normal 
passages of the train. The frame-cars have no own undercarriages at their 
ends adjacent to said intermediate bogie-truck, so that the two frame-cars 
and the intermediate bogie-truck form an assembled two-link unit that 
cannot be separated. 
In order to limit traffic hindrance during the track relaying operations it 
is in general prescribed that on double-track railroads the adjacent 
parallel track or siding must not be blocked. By this requirement the 
maximum width and the maximum length of the working cars are limited in 
such a way that even in short radius curves their clearance gauge or 
passage section must always have a sufficient distance from the passage 
section of the adjacent parallel track. 
SUMMARY OF THE INVENTION 
It is the essential purpose of this invention to provide an improved 
railroad track relaying train whereby all the operations consisting in 
removing the old ties and rails, and the excavation of the worn ballast, 
as well as the laying of new ties and new rails, are accomplished without 
stopping the machine and simultaneously with the removal of the old ties 
and rails, and in such a way that the train will still better fit within 
the maximal permissible moving dimensions or passage section while 
increasing the width of the working cars and reducing their wheelbase. 
These improvements together with other advantageous features to be 
described presently are obtained by providing working cars having bogie 
trucks at both ends and by interconnecting the working cars by means of 
coupling frames that carry the adjacent ends of said working cars and are 
supported by special trucks adapted to travel on the ballast and/or on the 
cleared track platform or sub-grade, or on the screened ballast, and 
adapted to be lowered more or less in relation to the relevant coupling 
frames, so as to raise adjacent ends of said working cars with their 
bogie-trucks in the trackless working area, and finally by the fact that 
each coupling frame interconnects two adjacent cars through the medium of 
universal joints and guide members for the purpose of maintaining the 
position of the working car concerned in relation to the coupling frame. 
This arrangement has the main advantage that two working cars equipped with 
usual on-track undercarriages at both ends, together with their 
intermediate coupling frame form a three-link group of vehicles which can 
better approximate a curve in a trackless working area than two directly 
coupled working cars. 
Moreover the working cars have a larger width and a reduced wheel base.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The railroad track relaying train according to this invention may be 
constructed for carrying out two different methods of removing the old 
ties and the old rails: 
1. A method for removing and loading only the old ties (FIGS. 6, 8, 9 and 
13). The old rails 1 are spread apart and laid behind the machine either 
on the shoulder of the bedding or along the track axis. They are 
discharged at the end of the relaying operations. 
2. A method for removing complete track panels or spans with the assistance 
of a rotary elevator 26 adapted to lift and turn the track panels upside 
down and to lay them upon lorries 41 rolling on a transport runway or 
level 40 so as to be eventually discharged by means of gantries (FIGS. 10, 
12 and 15). 
The railroad track relaying train comprises six main component elements 
shown diagrammatically in FIGS. 1, 2, 14 and 16, namely a screener car 4 
(shown only in FIG. 16), a track removing car 5, a ballast-clearing or 
excavating car 6, a track-relaying car 7, and (shown in FIG. 14) a 
tie-screw fitting car 46 followed by transporting cars 47, and gantries 48 
and 49 connected by girder 50 equipped with a transport beam (not shown). 
The car 4 with the ballast screening machine and the tie-screw fitting car 
46 are conventional two-bogie-truck cars. The track removing car 5, the 
ballast-clearing car 6 and the track-relaying car 7 constitute together a 
hinged sequence of wagons supported by six bogie-trucks 12 to 17 and 
interconnected by coupling frames 8 and 8' each of which is equipped with 
a caterpillar or track-laying truck 11 and 11' respectively. Although 
various conveyors cross over coupling frames 8 and 8' (FIGS. 6 and 10), no 
track working tools or equipment are mounted on these frames. 
During the track relaying operations, the screener 4 and the first 
bogie-truck 12 of the track removing car 5 run on the former track 1. The 
central section of the train bears on the caterpillar or track-laying 
trucks 11 and 11' rolling the leading one on the ballast and the trailing 
one on the excavated track platform, or on the screened ballast. The 
rear-bogie-truck 17 of the track relaying car 7 as well as the tie-screw 
fitting car 46 run on the new track 1'. Each coupling frame 8, 8' 
interconnects two adjacent working cars by means of universal or Cardan 
joints 9. Guide members 10 provided at one end of each working car are 
resting on the adjacent end of the respective coupling frame (FIGS. 2, 3, 
6, 10) for keeping the chassis of the car concerned in the proper 
transverse parallel position in relation to the coupling frame 8. The 
other end of each working car can freely incline with respect to the 
adjacent coupling frame when the train passes through a banked curve. 
Controlled hydraulic bumpers 42 are also provided for guiding the relevant 
coupling frame 8, 8' in a predetermined longitudinal position with respect 
to the car chassis or, if the train is moving in a curve, in a 
predetermined angle with respect to said car chassis, as shown in FIG. 5. 
FIGS. 6 and 7 illustrate schematically the arrangement of the caterpillar 
truck 11 and its coupling frame 8. The other caterpillar truck 11' and its 
coupling frame 8' are built up in the same way. 
According to FIGS. 6 and 7 the caterpillar truck 11 has a pair of track 
members 61, 62 (FIG. 7) and is equipped with lifting means 58 comprising 
hydraulic cylinders for lowering and lifting the truck in relation to its 
coupling frame 8. Each of the caterpillar track members 61 and 62 at both 
sides of the caterpillar truck 11 is driven individually by adequate 
hydrostatic drive means 59 and 60 that provide an infinitely variable 
working speed and allow the guiding and steering of the caterpillar truck 
11 along a curve in a conventional manner by driving one caterpillar track 
member 61, 62 at one side with a lower or a higher speed than the other 
one at the other side. 
Automatic control or servo means 63 (FIG. 7) are provided which control 
during the operations the drive and steering means, that is the 
hydrostatic drive means 59 and 60, so that the caterpillar truck 11 
follows the trace of the former track 1 or a trace parallel thereto when 
it is desired to change the distance between parallel tracks. 
For this reason the automatic control or servo means 63 may be controlled 
in different ways to guide and steer the caterpillar trucks. 
This control can be accomplished by using the parallel adjacent track 2 
(FIGS. 3 and 7) or a span wire 3 (FIG. 4) as a reference base, this wire 3 
being tensioned along a polygonal line approching the trace of the track. 
Feeler devices 54 with extensible or telescoping rail feelers 55 (FIGS. 3 
and 7) or feeler devices 56 with extensible or telescoping feeler rollers 
57 (FIG. 4) mounted on the caterpillar trucks 11, 11' sense the parallel 
track 2 or the span wire 3, respectively, and measure continously the 
distance between said reference base and the caterpillar trucks, this 
distance being a measure for the desired run of these trucks, and a 
corresponding control signal is transmitted to the servo means 63 for 
steering the caterpillar trucks. The same measuring and controlling 
principle known per se may be used for adjusting the tie-laying machine on 
the working car 7. 
For assisting the guiding of the coupling frames and for maintaining them 
in a predetermined position with respect to the adjacent working car it is 
preferable to have the already mentioned hydraulic bumpers 42 whose length 
can be individually controlled. In this way the distances on both sides 
between a coupling frame and the adjacent working car can be defined by 
the respective controlled lengths of the two bumpers 42 as shown in FIG. 5 
for the coupling frame 8 and the working car 6 when passing a curve. 
FIG. 16 illustrates another way for controlling the servo means 63 (and 
also the tie-laying machine) by using an angle reference and measuring 
system for determining the trace of the caterpillar trucks. This system 
comprises at least the angles .alpha.,.beta., .gamma., .delta. and 
.epsilon. between the longitudinal axes of successive adjacent cars and of 
working cars and adjacent coupling frames, respectively, beginning with 
the angle .alpha. between the screener car 4 that is still wheeling 
completely on the former track 1 and the track removing car 5. These 
angles may be measured by known electrical angle-measuring instruments in 
the form of a rotary potentiometer 64 mounted at or near the linking or 
coupling point a, b, c, d and e between adjacent cars 4, 5 and between a 
car and the adjacent coupling frame 5,8; 8,6; 6,8' and 8',7, respectively. 
The measured angle .alpha. indicates always the curvature of the former 
track 1 near the beginning of the working area and represents therefore a 
reference value signal that is transmitted to the servo means 63 and from 
which the corresponding steering signals for the steering means are 
obtained or derived. The measured angles .beta., .gamma., .delta. and 
.epsilon. indicate the actual values of the path followed by the 
caterpillar trucks, and the steering operations are carried out so that 
these actual angles approach as exact as possible to the reference angles 
derived from the measured angle .alpha.. Since the curvature of a track 
curve is in general constant, all angles must be maintained equal and 
constant once the train has entered the curve. 
Naturally it is also possible to use other known angle-measuring devices 
e.g. known optical angle-measuring instruments. Moreover it may be useful 
to include further reference angles to be measured between other adjacent 
cars of the train wheeling ahead of the working area and/or behind the 
working area on the new track 1', as between the track relaying car 7 and 
the tie fixing car 46 (FIG. 14), so that the curved path to be followed by 
the caterpillar trucks could be derived more exactly if necessary. 
It will be obvious to those skilled in the art that in principle every 
known measuring and reference system, which is used for railroad 
track-laying or track-maintenance machines as track levelling, aligning 
and tamping machines (e.g. U.S. Pat. No. 3,314,154, G.B. Pat. No. 
1,479,230) can also be applied to obtain the adequate control signals for 
the servo means 63 to control the steering means of the caterpillar 
trucks. By applying these known methods and measurement and control 
devices to the steering according to the present invention, devices 
responsive to the position of the former track 1 may be used, whereby this 
track 1 is measured by rail feelers mounted on the screener car 4 ahead of 
the working area. 
The sensing points of these rail feelers serve to derive or calculate the 
curvature of the former track 1 corresponding to the curved trace to be 
followed by the caterpillar trucks 8 and 8'. In FIG. 16 such a rail feeler 
70 is schematically shown in dotted lines. 
Finally the steering of the caterpillar trucks may also be accomplished by 
using manual control means whereby an operator controls the steering means 
according to reference marks fixed along the track; such marks are 
commonly used for track laying or correcting operations. 
The coupling frame 8 or 8' as described serves only to connect two working 
cars by a hinge member and to support and move them in the trackless 
working area, without carrying any working machine or working head. In 
this way two working cars and their coupling frame representing a sort of 
intermediate chain link form a three-link group of vehicles instead of a 
two-link group that would result if the two working cars would be coupled 
directly. This has the principal advantage, that in a curve the length of 
overhang of the working cars can be reduced and that even cars being 
rather large in width remain in the prescribed passage section if they run 
through a curve. 
Another advantage consists in a very simple construction of the coupling 
frame 8, 8' which does not have to carry any working machines or working 
heads and which does not need any on-track undercarriages. A further 
advantage is the fact that the working cars are equipped with usual 
on-track undercarriages or bogie trucks 12,13; 14,15; 16,17 at both ends; 
therefore outside the trackless working area they can run on the rails 
like a normal car and independently of any coupling frame. 
The track removing car 5 (FIGS. 1 and 6) is supported at the front by the 
bogie-truck 12 and at the rear through the intermediary of the hinged 
coupling frame 8 supported in turn by the relevant caterpillar truck 11. 
Mounted on the car 5 are the conveyors 18 for the excavated material and 
the overhead conveyors 19 for the reclaimed ballast. The old ties 32 are 
removed and transported by using a hydraulic excavator or digger 20, 
endless-chain conveyors 21 and an elevator 22. 
Behind the bogie-truck 12, roller-type rail-jacks (not shown) are provided 
for lifting and spreading apart old rails 1 which are subsequently 
transferred along the machine and eventually laid at the rear upon the 
track sub-grade or platform or along the track axis. 
In the exemplary form of embodiment illustrated in FIGS. 6, 8 and 9, the 
hydraulic excavator or digger 20 extracts the old ties 32 one by one from 
the ballast and lays them down upon an endless chain conveyor 21 directing 
the old ties onto a storage conveyor 21'. The elevator 22 comprises a 
pivoting arm 36 and a rotary clamping head 37 and is adapted to pick up 
three ties 32 at a time from the storage conveyor 21', lift and pivot 
these ties backwards by means of the pivoting arm 36, thus causing them to 
rotate through 90 degrees in the track plane with the rotary clamping head 
37 (FIG. 9). Then the elevator 22 lifts the turned ties 33 laterally of 
the old-ballast conveyor 18, above the level of the tie conveyor 23 (FIG. 
8). The ties are subsequently pivoted and rotated forwards still in the 
plane of the underlaying track and finally laid upon the conveyor 23 which 
transfers them to the transport gantries. The elevator is then returned 
through the same path to its initial position. 
All the movements of the working cycle may be controlled automatically or 
manually. 
Alternatively, the track removing car 5 may be equipped with an elevator 22 
arranged for lifting and pivoting the ties in the track plane around both 
conveyors 18 for the old ballast and 19 for the screened ballast, 
respectively. 
In another form of embodiment of the invention illustrated in FIG. 13, the 
rotary elevator 43 provided with hydraulic claws 44 mounted on a lifting 
system is adapted to grip three ties at a time from the storage conveyor 
and to lift them against the elevator. The latter turns the ties around 
the old ballast conveyor 18 and screened ballast conveyor 19, and 
eventually deposits the ties upside down upon the top level from which 
they are picked up by the movable conveyor 45 and transferred to the 
gantries. Then, the elevator 43 resumes its initial position. All the 
movements of the cycle are controlled automatically or manually. 
Alternatively, the tie removing car 5 may be provided with an elevator 43 
adapted to turn the ties only around the old ballast conveyor 18 as in the 
case illustrated in FIG. 8, but in this modified version the ties are 
disposed upside down on the conveyor 45. 
In another specific form of embodiment for removing complete track panels 
or spans 34, as illustrated in FIGS. 10 and 12, the track removing car 5 
comprises a central girder 24 in which the conveyor 18 for the excavated 
material is housed, the conveyor 19 for the reclaimed ballast being 
located overhead. A rotary elevator 26 equipped with hoisting means and a 
runway 40 for the lorries 41 is suspended by means of rollers 27 from the 
central girder 24. The hoisting means comprises two pairs of rolling claws 
28 secured to hinged frames 29, with hydraulic cylinders for lifting and 
moving said claws laterally. The track panels are disposed upside down on 
the lorries 41 rolling on runway 40. 
In a modified version of this embodiment according to FIG. 15, the track 
removing car 5 may be equipped with a rotary elevator 43' similar to FIG. 
13, adapted to lift and rotate the track panels 34 by means of rolling 
claws 28 secured to hinged frames 29 (as in FIG. 12) both around the old 
ballast conveyor 18 and around the screened ballast conveyor 19, so that 
the track panels are disposed upside down on lorries rolling on runway 40' 
above conveyor 19. 
The track panels may be removed without discontinuing the operation of the 
machine. During the picking up of the next track panel, the one stored on 
the ballast-clearing machine is moved forwards by another train of lorries 
until it reaches the relaying car 7 where it is taken over by the gantries 
48, 48 (FIG. 14) and transported on loading wagons. 
The ballast clearing car or machine 6 (FIG. 1) comprises a pair of 
bogie-trucks 14, 15, an excavator 30, a ballast metering unit and means 
for transporting the ballast, the track ties or the track spans or panels. 
This car 6 is coupled at its leading end to the track removing car 5 and 
at its trailing end to the track-relaying car 7, both couplings occuring 
through the hinged connecting frame 8, 8' supported by the caterpillar 
truck 11, 11'. During the track relaying operations, the track clearing 
machine is supported by the pair of caterpillar trucks 11 and 11' running 
on the old ballast and the excavated track platform, or on the screened 
ballast. 
The excavator 30 comprises an excavating chain and an equalizing or 
levelling blade 25 FIG. 11. The excavator is pivotally mounted on the 
frame and suspended by means of hydraulic cylinders so that the working 
depth and inclination of the platform can be adjusted at will. The blade 
is provided with side plates adjustable during the operation of the 
machine by means of hydraulic cylinders. Behind the levelling blade 25 a 
tamper is provided for compacting the track platform. 
The material dug by the excavator is delivered by the excavating chains to 
conveyors 18 and thus directed towards the screener. The reclaimed and 
screened ballast is then directed by conveyors 19 to the rear end of the 
train and fed to the reclaimed-ballast metering device comprising a fixed 
bin and a metering element adjustable in the vertical direction as a 
function of the requisite thickness of the ballast layer. From the storage 
bin, the ballast is fed to the metering device to provide the first 
ballast layer and the excess ballast is delivered to an intermediate 
conveyor and thus fed to the ballast distributor mounted on the track 
relaying car. Behind the ballast metering device a tamper is also provided 
for compacting the ballast before laying the ties. 
The relatively long transport path followed by the old ballast and by the 
screened ballast along the train may become an inconvenience when the 
train is stopped for any reason during its operation. It would be 
necessary to stop all the conveyors carrying excavated and screened 
material for preventing an unequal distribution of the ballast beneath the 
laying car. Now starting all the loaded conveyors simultaneously would 
constitute a heavy demand of electric power and might delay the resumption 
of normal operations. To avoid these drawbacks, the present invention 
provides a transport connection established at will but preferably 
automatic each time the train is stopped. To this end, a hopper 31 located 
as close as possible to the excavating chain is disposed between the 
transport chains 18 for the old ballast and 19 for the screened ballast. 
The transport connection, creating a closed-circuit condition between the 
screened ballast and the used ballast, is obtained by shifting the 
screened ballast conveyor 19' with the assistance of a hydraulic cylinder 
39 when the machine is stopped (FIG. 11). 
The track relaying car 7 provided with two bogie-trucks 16 and 17 is 
equipped with tie-laying means, together with the conveyor elements, the 
rail laying members and the ballast distributor. During operation, the car 
7 is caused to bear at its front end on the caterpillar-mounted coupling 
frame 8' and at its rear end on the bogie-truck 17 rolling on the new 
track 1'. Also mounted on the rear portion of the car 7 are the new rails 
laying members comprising, inter alia, roller claws, clamps or nippers. 
The new ties 52 stored on transport cars 47 (FIG. 14) are transferred by 
means of gantries 48, 49 to a storage conveyor 51 of the car 46 equipped 
with the tie-screw fitting means. An intermediate conveyor separates the 
ties and feeds them to rotary clamps disposed at the rear end of the track 
relaying car 7. These clamps lift and turn two ties at a time, and lay 
them upon a longitudinal conveyor divided into several sections for the 
intermediate storage. The ties 52 are thus transferred by the longitudinal 
conveyor to the tie-laying machine where they are centered, positioned and 
finally laid upon the ballast, as shown schematically by arrow 53 in FIG. 
14. 
The relative spacing of the ties thus laid down is set by means of a 
measuring device adapted to change this spacing centimeter by centimeter. 
The ties are also positioned in the transverse direction either by means 
of a feeler controlling the distance between the tie axis and the parallel 
track or by means of a measuring system associated with adequate control 
means provided on the working car. 
The tie-screw fitting car 46 (FIG. 14) comprises power-wrenches for 
fastening the new rails by means of tie-screws. Moreover, this car 46 is 
used for transporting the gantries 48 and 49. The dimensions of this car 
46 are such that crew can fit the tie fastening means from inside the car. 
The pair of self-propelled gantries 48 and 49 is constructed according to 
the teachings of Swiss Pat. No. 549,692, for transporting the old and new 
ties to and from the working cars and the transport cars 47. These two 
gantries 48, 49 are intereconnected by the central girder 50 from which a 
tie transporting beam (not shown) is suspended by means of ropes and 
hydraulic cylinders. It also comprises hydraulically actuated claws for 
gripping the ties or the track panels. 
The complete relaying of a railroad track according to the instant 
invention comprises the following operations: 
I--Removing the old ties and rails or the old track panels. 
In the first case: Removing the rail fixing means in front of the machine; 
spreading the old rails apart, behind the front bogie-truck of the rail 
removing car, with the assistance of rolling claws; extracting the old 
ties by using the hydraulic excavator and transferring them through the 
chain conveyors and an elevator to the storage conveyor at the laying car. 
In the second case: Removing the old track panels by means of the rotary 
elevator, then laying them upon the lorries and transporting them in two 
successive runs to the laying car. 
II--Excavating the ballast, equalizng and compacting the track sub-grade or 
platform; 
III--Screening the ballast by using a vibrating screen and a rotary screen; 
the reclaimed ballast is transported to the metering device behind the 
excavation chain and to the ballast distributor at the rear end of the 
track relaying car; any refuse is either deposited laterally of the track 
platform or loaded into a special car; 
IV--Laying the new ties by using the tie laying apparatus; 
V--Laying the new rails on the ties by using rotary claws in front of the 
rear bogie-truck of the track relaying car; 
VI--Transporting the old ties or, as the case may be, the old track panels, 
by using the gantries to the transport cars and supplying new ties by 
using the gantries from the transport cars to the relaying car. 
VII--Fixing the rails by using the tie-screw fastening means contemplated. 
FIGS. 17 and 18 illustrate another embodiment of a coupling frame 
connecting two working cars 5 and 6. This coupling frame 65 is supported 
by two caterpillar trucks 66 and 66' at both ends. Each caterpillar truck 
has a pair of caterpillar truck members and is mounted on a turntable and 
rotatable about a vertical axis 68, 68'; it can be steered by hydraulic 
cylinders 67, 67' that act in a horizontal transversal direction between 
the understructure of the respective truck and the chassis of the coupling 
frame 65 and therefore control the rotation of the truck 66, 66' about 
said axis 68 or 68'. Moreover each caterpillar truck is equipped with 
feelers 54 for sensing the parallel track 2 as described in connection 
with FIG. 3. Hydrostatic drive means (not shown) serve to drive the 
caterpillar trucks, lifting means (not shown) are adapted to raise or to 
lower the coupling frame 65 in relation to the caterpillar trucks, and 
servo means may be provided for an automatic steering and guiding as 
described in connection with FIG. 7. 
The provision of two steerable caterpillar trucks 66 and 66' at both ends 
of a coupling frame 65 improves and facilitates in general the steering 
operations and steering movements in a curve and allows to trail a given 
curved path in a more exact manner.