Field of the Invention

[0001] This invention relates to railway track maintenance. More particularly, the invention relates to a ballast excavator for use in railway track maintenance operations. The invention also relates to a ballast undercutter, and also to an endless chain structure for use in ballast maintenance operations.

Background Art

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Ballast is considered the foundation upon which railway tracks are placed. Typically, a railway track comprises railway lines supported on railway sleepers in known manner, with the railway sleepers resting on a bed of ballast material. The ballast aids in supporting the load from the sleepers and acts as an avenue for water drainage. Over time ballast bed can be worn or fouled, necessitating periodic track maintenance.

[0004] Typically, the maintenance involves excavating ballast material from the ballast bed and distributing replenishment ballast material to the ballast bed to replace the excavated ballast.

[0005] Known ballast excavators, also known as ballast undercutters, comprise large cutter bars mounted on compact excavators which function as off-track maintenance machines. Initially a skid loader is utilised to remove the ballast shoulders. The undercutter equipped excavator then moves alongside the railway track and wedges the ballast undercutter bar underneath the sleepers to remove worn ballast. The worn ballast is then displaced to a position behind the excavator by the cutter bar to be removed or collected by a skid loader. Replacement ballast would then be deposited after the removal of the used ballast by an appropriate method.

[0006] This procedure for ballast excavation typically requires various other machines to operate alongside the ballast undercutter to facilitate removal and collection of the ballast. Such an arrangement of machines typically inhibits operation in confined locations such as tunnels. Further, a variety of skilled machine operators are required for the maintenance to proceed.

[0007] It is against this background that the present invention has been developed.

Disclosure of the Invention

[0008] It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice.

[0009] Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed.

[0010] According to a first broad aspect of the present invention there is provided an apparatus comprising an undercutter portion for excavating ballast material from a ballast bed and a conveyor portion for conveying the excavated ballast material to a discharge zone, wherein there is provided an endless chain structure adapted to move along a path which includes the undercutter portion and the discharge portion, the endless chain structure defining part of the undercutter portion and the endless chain structure further defining part of the conveyor portion. [0011] Preferably, the endless chain structure comprises a plurality of chain parts interconnected for pivotal movement one with respect to another, each chain part being pivotally connected to an adjacent chain part about a respective one of three axes being a first pivot axis, a second pivot axis and a third pivot axis, wherein the first, second and third axes are substantially perpendicular to the longitudinal extent of the chain structure, and wherein the first and second axes are substantially parallel and the third axis is substantially perpendicular to the first and second axes.

[0012] Preferably, the endless chain structure comprises a plurality of chain links connected one to another for pivotal movement about respective first axes, each link comprising first, second and third link sections each defining one of said chain parts, the first link section being pivotally connected to an adjacent link for pivotal movement therebetween about the respective first axis, the third link section being pivotally connected to a further adjacent link for pivotal movement therebetween about the respective first axis, and the second link section being interposed between the first and third link sections, the first and second link sections being interconnected for pivotal movement therebetween about the respective second axis and the second and third link sections being interconnected for pivotal movement therebetween about the respective third axis.

[0013] Preferably, each link section is configured to define a respective peripheral face, wherein the peripheral faces of the link sections in each link cooperate to define a link face, and wherein the link faces in the endless chain cooperate to define a chain face.

[0014] Preferably, the endless chain structure further comprises excavating means adapted to engage and excavate ballast material from the ballast bed.

[0015] Preferably, the excavating means comprises a plurality of excavating tools spaced along the endless chain.

[0016] Preferably, each excavating tool is configured as an excavating claw. [0017] Preferably, the excavating claw comprises a plurality of excavating fingers spaced transversely to the longitudinal extent of the endless chain structure.

[0018] Preferably, the excavating claw further comprises a base from which the excavating fingers extend, the base presenting a contact face transverse to the longitudinal extent of the endless chain structure.

[0019] Preferably, the contact face is curved to present a concave surface to ballast material.

[0020] Preferably, the excavating fingers extend forwardly and outwardly from the base with respect to the direction of travel of the endless chain structure.

[0021] Preferably, each excavating claw is mounted on the chain face.

[0022] Preferably, each excavating claw is mounted on a respective chain link.

[0023] Preferably, each excavating claw is mounted on one of the link sections of the respective link.

[0024] Preferably, the chain face is adapted to define a load-carrying surface of the conveyor portion.

[0025] Preferably, the conveyor portion further comprises two longitudinal side portions defining an elongate space therebetween, wherein the endless chain structure has a portion of the path thereof passing along the space, whereby the two side portions and the endless chain structure therebetween cooperate to define the conveyor portion.

[0026] According to a second broad aspect of the invention there is provided a mobile machine comprising an apparatus according to the first broad aspect of the present invention. [0027] Preferably, the mobile machine is configured for movement along a railroad having railway tracks supported on the ballast bed.

[0028] Preferably, the mobile machine is configured as a road/rail vehicle for dual mode mobility, one mode being a rail mode in which the vehicle is supported for movement on the railway track and the other mode being a road mode in which the vehicle is adapted to travel on ground or a road surface.

[0029] Preferably, the mobile machine further comprises a lifting means for lifting and supporting the railway track as ballast is excavated.

[0030] Preferably, the mobile machine comprises two apparatus according to the first broad aspect of the present invention adapted to operate from opposite sides of the ballast bed.

[0031] Preferably, the respective undercutter portions of the two apparatus are offset with respect to each other in the longitudinal direction of travel of the mobile machine.

[0032] According to a third broad aspect of the present invention there is provided a ballast excavating machine incorporating an apparatus according to the first broad aspect of the present invention.

[0033] According to a fourth broad aspect of the present invention there is provided an endless chain structure for a ballast undercutter comprising a plurality of chain parts interconnected for pivotal movement one with respect to another, each chain part being pivotally connected to an adjacent chain part about a respective one of three axes being a first pivot axis, a second pivot axis and a third pivot axis, wherein the first, second and third axes are substantially perpendicular to the longitudinal extent of the chain structure, and wherein the first and second axes are substantially parallel and the third axis is substantially perpendicular to the first and second axes. [0034] Preferably, the chain structure comprises a plurality of chain links connected one to another for pivotal movement about respective first axes, each link comprising first, second and third link sections, the first link section < being pivotally connected to an adjacent link for pivotal movement therebetween about the respective first axis, the third link section being pivotally connected to a further adjacent link for pivotal movement therebetween about the respective first axis, and the second link section being interposed between the first and third link sections, the first and second link sections being interconnected for pivotal movement therebetween about the respective second axis and the second and third link sections being interconnected for pivotal movement therebetween about the respective third axis.

[0035] According to a fourth broad aspect of the present invention there is provided an endless chain structure comprising a plurality of links connected one to another for pivotal movement about respective first axes, each link comprising first, second and third link sections, the first link section being pivotally connected to an adjacent link for pivotal movement therebetween about the respective first axis, the third link section being pivotally connected to a further adjacent link for pivotal movement therebetween about the respective first axis, and the second link section being interposed between the first and third link sections, the first and second link sections being interconnected for pivotal movement therebetween about a second axis and the second and third link sections being interconnected for pivotal movement therebetween about a third axis.

[0036] According to a fifth broad aspect of the present invention there is provided a ballast undercutter comprising an undercutter portion for excavating ballast material from a ballast bed, the undercutter portion comprising a plurality of chain parts interconnected for pivotal movement one with respect to another, each chain part being pivotally connected to an adjacent chain part about a respective one of three axes being a first pivot axis, a second pivot axis and a third pivot axis, wherein the first, second and third axes are substantially perpendicular to the longitudinal extent of the chain structure, and wherein the first and second axes are substantially parallel and the third axis is substantially perpendicular to the first and second axes.

[0037] According to a sixth broad aspect of the present invention there is provided a method of excavating ballast material using apparatus according to the first broad aspect of the present invention.

[0038] According to a seventh broad aspect of the present invention there is provided a method of excavating ballast material using a ballast undercutter according to the fifth broad aspect of the present invention.

Brief Description of the Drawings

[0039] The invention will be better understood with reference to the following description of one specific preferred embodiment thereof as shown in the accompanying drawings/photographs in which:

Figure 1 is a side view of a ballast excavating machine according to the preferred embodiment;

Figure 2 is a rear perspective view of the. ballast excavating machine;

Figure 3 is a fragmentary side view of a ballast excavating machine;

Figure 4 is a front perspective view of the ballast excavating machine, with each excavating and conveying assembly in a retracted condition;

Figure 5 is a further front perspective view of the ballast excavating machine, but with each excavating and conveying assembly in an extended condition;

Figure 6 is a side view of the arrangement shown in Figure 5; Figure 7 is a rear perspective view of the arrangement shown in Figure 5;

Figure 8 is a front view of the arrangement shown in Figure 5;

Figure 9 is a rear view of the arrangement shown in Figure 5;

Figure 10 is a further fragmentary perspective view of the arrangement shown in Figure 5;

Figure 11 is a further fragmentary perspective view of the arrangement shown in Figure 5, illustrating in particular the excavating and conveying assembly;

Figure 12 is a further rear perspective view of the arrangement shown in Figure 5;

Figure 13 is a view illustrating in particular the excavating and conveying assembly;

Figure 14 is a view illustrating the upper end of the conveyor portion of the excavating and conveying assembly and a conveyor system onto which excavated ballast material is transferred;

Figure 15 is a schematic side view of the excavating and conveying assembly, including an endless chain structure incorporated in the undercutter portion and the conveyor portion;

Figure 16 is a fragmentary perspective view illustrating in particular the excavator portion of the excavating and conveying assembly,;

Figure 17 is a further fragmentary perspective view illustrating in particular the excavator portion of the excavating and conveying assembly; Figure 18 is a still further fragmentary perspective view illustrating in particular the excavator portion of the excavating and conveying assembly;

Figure 19 is a fragmentary perspective view illustrating in particular the transition between excavator portion and the conveyor portion of the excavating and conveying assembly;

Figure 20 is a further fragmentary perspective view illustrating the transition between excavator portion and the conveyor portion of the excavating and conveying assembly;

Figure 21 is a still further fragmentary perspective view illustrating the transition between the excavator portion and the conveyor portion of the excavating and conveying assembly;

Figure 22 is schematic plan view depicting the endless chain structure forming part of the undercutter and conveyor portions;

Figure 23 is a schematic side view of part of the endless chain structure;

Figure 24 is a fragmentary view of the endless chain structure illustrating in particular excavating claws provided thereon;

Figure 25 is a further fragmentary view of the endless chain structure at the transition between the excavator portion and the conveyor portion, illustrating in particular the excavating claws;

Figure 26 is a further fragmentary view of the endless chain structure extending along the conveyor portion, illustrating in particular the excavating claws;

Figure 27 is a further fragmentary view of the endless chain structure at the transition between the excavator portion and the conveyor portion; Figure 28 is a still further fragmentary view of the endless chain structure at the transition between the excavator portion and the conveyor portion, illustrating in particular the excavating claws;

Figure 29 is a schematic view of an excavating claw provided on the endless chain structure;

Figure 30 is a perspective view of several links of the endless chain structure;

Figure 31 is a perspective view of a model illustrating one link of the endless chain structure, with the link comprising three link sections pivotally interconnected and the three link sections being shown in one particular orientation;

Figure 32 is a side view of the arrangement shown in Figure 31 ;

Figure 33 is a further perspective view of the arrangement shown in Figure 32;

Figure 34 is a fragmentary perspective view illustrating in particular a rail lifting mechanism; and

Figure 35 is a side view of the rail lifting mechanism. Best Mode(s) for Carrying Out the Invention

[0040] The preferred embodiment shown in the drawings/photographs is directed to a ballast excavating machine 10 for excavating ballast from a ballast bed 13 of a railway track 15.

[0041] The railway track 15 comprises two railway lines 17 supported on railway sleepers 19 in known manner, with the railway sleepers resting on the ballast bed 13. With this arrangement, the ballast bed 13 comprises a central section 21 upon which the sleepers 19 are resting and two shoulder sections 23 on opposed sides of the railway track 15. Each railway line 17 comprises a series of rails 18 connected one to another in end-to-end relation.

[0042] The operation performed by the ballast excavating machine 10 involves excavating ballast material from the ballast bed 13 prior to delivery of replenishment ballast material to the ballast bed in replacement of the excavated ballast.

[0043] The ballast excavating machine 10 comprises a vehicle 30 having a frame structure 33 and a cabin 35 to accommodate an operator. The frame structure 33 is supported on wheels 39.

[0044] The ballast excavating machine 10 can assume an operative condition for performing an excavating operation and a transport condition, as will be described in more detail later. In the transport condition, the ballast excavating machine 10 is preferably so configured that the vehicle 30 complies with road transport regulations in Australia, whereby it can legally travel on public roadways.

[0045] In the arrangement shown, the vehicle 30 comprises a conventional truck 31 having a cab 36 and a chassis 37 modified to provide the frame structure 33. Various other modifications are made to the truck 31 to configure it as the vehicle 30. In should, however, be appreciated that the vehicle 30 can be constructed specifically for the intended purpose.

[0046] The wheels 39 are configured for dual mode mobility, one mode being a rail mode in which the vehicle 30 is supported for movement along the two railway lines 17, and the other mode being a road mode in which the vehicle 30 is adapted to travel off the two railway lines 17 (typically, along the sleepers 19 on the outer side of the railway lines 17, along ground adjacent to the railway track 15, or along a roadway). In other words, the machine 10 has a road/rail mobility configuration. In the arrangement shown, the dual mode mobility is provided by the wheels 39 being configured in two sets, one set being configured as rail wheels 41 and the other set being configured as road wheels 43. In the arrangement illustrated, the road wheels 43 comprise the original wheels of the truck 31 , with modifications being made to the truck to incorporate the rail wheels 41. A control mechanism (not shown) is provided for selectively moving the rail wheels 41 between operative and retracted conditions, as is known practice, whereby in the operative condition the rail wheels engage the railway lines 17 and the road wheels 43 are lifted into an elevated position above the ground, and in the retracted condition the rail wheels are above the railway lines 17 and the road wheels remain in contact with the ground. With this arrangement, the vehicle 30 assumes a rail mode when the rail wheels 41 are in the operative condition and a road mode when the rail wheels 41 are in the retracted condition.

[0047] In this preferred embodiment, the vehicle 30 is operated from cabin 35 when in the rail mode and performing a ballast excavating operation, and is operated from the cab 36 when in the road mode. More particularly, when in the road mode, the vehicle 30 is driven as if it were the truck 31 , with the driver in the cab 36 operating the truck in the normal manner.

[0048] When in the road mode, the vehicle 30 is driven in the forward direction of the truck 31. However, when in the rail mode and performing a ballast excavating procedure, the vehicle 30 is driven in the rearward direction of the truck 31.

[0049] The ballast excavating machine 10 is configured to travel along a railway track 15 to excavate the central section 21 and the two shoulders section 23 of the ballast bed 13. This is particularly suitable for long stretches of railway track with simple track layout configurations.

[0050] The ballast excavating machine 10 comprises excavating means 51 for excavating ballast material in the central section 21 and the two shoulder sections 23 of the ballast bed 13. [0051] The excavating means 51 comprises two excavating and conveying assemblies 55 disposed for operation from opposed sides of the railway track 15.

[0052] The two excavating and conveying assemblies 55 project inwardly and operate in unison from opposed sides of the railway track 15.

[0053] Each excavating and conveying assembly 55 comprises an undercutter portion 57 and a conveying portion 59.

[0054] The two undercutter portions 57 are offset with respect to each other in the longitudinal direction of travel of the machine 10, as best seen in Figure 22.

[0055] Each excavating and conveying assembly 55 further comprises an endless chain structure 61 adapted to move along a circuitous path 63 which includes the undercutter portion 57 and the conveying portion 59. The endless chain structure 61 is supported on and passes around a series of sprockets 64, at least one of which is powered to drive the chain structure 61.

[0056] In this preferred embodiment, the chain structures 61 are powered from a hydraulic power source.

[0057] The circuitous path 63 of the chain structure 61 travels through three dimensions in space; that is, path 63 has both horizontal and vertical vectors at various stages, as will become apparent later. It is a particular feature of the preferred embodiment that the endless chain structure 61 is constructed to accommodate such complex movement in three dimensions.

[0058] Each undercutter portion 57 is configured as a boom structure 65 adapted to move into, and along, the ballast bed 13 below the railway sleepers 19, as will be described in more detail later. Each boom structure 65 is adapted to enter the ballast bed 13 from the respective side thereof, passing through the adjacent shoulder section 23 and into the central section 21 below the below the railway sleepers 19. [0059] The boom structure 65 has provision for constraining and guiding the endless chain structure 61 along its path.

[0060] Within the boom structure 65, the endless chain structure 61 has an entry run 67 and a return run 69. With this arrangement, ballast material is excavated from the ballast bed 13 by the endless chain structure 61 along the return run 69 thereof. The configuration is such that the return run 69 is disposed forwardly of the entry run 67 with respect to the direction of travel of the machine 10 along the railway track 15 during an excavating operation.

[0061] The return run 69 moves the excavated ballast material to the conveyor portion 59 whereupon the excavated ballast material is conveyed by the conveyor portion 59 to a transfer zone 71. At the transfer zone 71 , the excavated ballast material is transferred onto a conveyor system 72 arranged to convey the excavated ballast material to a discharge zone 73 at which the excavated ballast is discharged from the ballast excavating machine 10.

[0062] In the arrangement shown, the excavated ballast is discharged from the ballast excavatingmachinelO and deposited onto the ground area alongside the railway track 15, as is known practice with ballast excavating operations. In another arrangement, there may be a ballast cleaner operating in conjunction with the ballast excavating machine 10, in which case the excavated ballast may be discharged from the ballast excavating machine and delivered to the ballast cleaner for cleaning the excavated ballast material. In yet another arrangement, there may be a mobile collection facility (such as a truck) operating in conjunction with the ballast excavating machine 10 to receive the excavated ballast material, whereby the excavated ballast is discharged from the ballast excavating machine and delivered to the mobile collection facility.

[0063] In the arrangement illustrated, the conveyor system 72 includes a series of conveyor sections 74 arranged to receive excavated ballast material from each of the conveyor portions 59 of the two excavating and conveying assemblies 55. [0064] The conveyor sections 74 include two receiving conveyors 75, each associated with a respective one of the two the conveyor portions 59. The two receiving conveyors 75 are movable between extended and retracted conditions corresponding to the operative and transport conditions of the vehicle 30. The two receiving conveyors 75 are shown in the retracted conditions in the drawings/photographs. The conveyor sections 74 further include a common intermediate transfer conveyor 76 and a common terminal discharge conveyor 77, the arrangement being that the common intermediate transfer conveyor receives excavated ballast material from the two receiving conveyors 75 and transfers that material to the common terminal discharge conveyor which in turn conveys the material to the discharge zone 73.

[0065] The common intermediate transfer conveyor 76 is mounted longitudinally on the frame structure 33. The common terminal discharge conveyor 77 is mounted on the frame structure 33 for movement between extended and retracted conditions. In the arrangement shown, the common terminal discharge conveyor 77 is pivotally movable between the extended and retracted conditions. In the retracted condition, the common terminal discharge conveyor 77 extends longitudinally with respect to the direction of travel of the vehicle 30, as shown in Figures 1 , 2 and 3. In the extended condition, the common terminal discharge conveyor 77 extends transversely with respect to the direction of travel of the vehicle 30, as shown in Figures 4, 9, 10 and 12 for discharging the excavated ballast material to one side of the vehicle 30 onto the ground area alongside the railway track.

[0066] The extended and retracted conditions of the common terminal discharge conveyor 77 respectively correspond to the operative and transport conditions of the vehicle 30.

[0067] Where there is ballast cleaning operating in conjunction with the ballast excavating machine 10, the cleaning process may involve the excavated ballast material undergoing a separation process to remove undersized components thereof as well as any unwanted debris. The retained cleaned ballast material may be redistributed in the ballast bed 13, in known manner.

[0068] Each excavating and conveying assembly 55 is selectively adjustable in position relative to the frame structure 33 on which it is supported.

[0069] In particular, each excavating and conveying assembly 55 is selectively movable between extended and retracted conditions respectively corresponding to the operative and transport conditions of the vehicle 30. The excavating and conveying assemblies 55 are shown in the retracted condition in Figures 1 to 4 and in the extended condition in Figures 5 to 13.

[0070] Further, each excavating and conveying assembly 55 has provision for positional adjustment relative to the ballast bed 13 when in the extended condition. In this way, the position of the undercutter portion 57 can be selectively varied with respect to the ballast bed 13 in order to accommodate characteristics of the ballast bed. In particular, such positional adjustment includes height adjustment of the undercutter portion 57 through the provision for vertical movement of the undercutter portion 57 relative to the frame structure 33. Additionally, such positional adjustment includes sideways adjustment of the undercutter portion 57 relative to the frame structure 33. In this way, the lateral position of the undercutter portion 57 can be selectively varied with respect to the ballast bed 13.

[0071] In the arrangement shown, each excavating and conveying assembly 55 is mounted as a unit on an adjustable support structure 78 which can be configured to provide the required positioning for the excavating and conveying assembly 55. The adjustable support structure 78 includes a telescopic arm assembly 79 for horizontal adjustment of the respective excavating and conveying assembly 55 and a telescopic leg assembly 80 for vertical adjustment of the excavating and conveying assembly 55. [0072] The facility for vertical adjustment provided by the telescopic leg assembly 80 not only accommodates height adjustment of the undercutter portion 57 relative to the ballast bed 13 but also allows the excavating and conveying assembly 55 to be elevated into a condition sufficiently clear of the ground for transportation when the vehicle 30 is in the transport condition.

[0073] Further, the facility for horizontal adjustment provided by the telescopic arm assembly 79 not only accommodates lateral adjustment of the undercutter portion 57 relative to the ballast bed 13 but also allows the excavating and conveying assembly 55 to be retracted into a fully withdrawn condition when the vehicle 30 is in the transport condition.

[0074] The endless chain structure 61 comprises a plurality of chain links 81 connected one to another by pivot pins 83 which define first pivot axes 85 transverse to the direction of travel of the endless chain structure 61.

[0075] Each chain link 81 comprises three link sections 87, being a leading link section 91 , an intermediate link section 93 and a trailing link section 95. The leading and intermediate link sections 91 , 93 are pivotally interconnected by pivot pin 97 for pivotal movement with respect to each other about a second pivot axis 99.

[0076] The intermediate and trailing link sections 93, 95 are pivotally interconnected by pivot pin 101 for pivotal movement with respect to each other about a third pivot axis 103.

[0077] The second pivot axis 99 is substantially parallel to the respective first axis 85 connecting the ends of the chain link 81 to an adjacent chain links in the endless chain structure 61.

[0078] The third pivot axis 103 is substantially perpendicular to the second pivot axis 99, and consequently substantially perpendicular to the first pivot axis 85. [0079] The first, second and third pivot axis 85, 99 and 103 are each perpendicular to the longitudinal extent of the endless chain structure 61.

[0080] The construction of the chain structure 61 involving the series of first, second and third axes provides an arrangement which can accommodate the circuitous path 63 which involves three dimensions.

[0081] Each link section 87 is comprises a body 105 configured to define a planar peripheral face 107. The various peripheral faces 107 of the link sections 87 cooperate to define a link face 109. The link faces 109 of the various chain links 81 in the endless chain structure 61 cooperate to define a chain face 111.

[0082] The chain face 111 supports excavating tools 113.

[0083] In this preferred embodiment, the excavating tools 113 are configured as excavating claws 115, with one excavating claw 115 mounted on each chain link 81. More particularly, each excavating claw 115 is mounted on the leading link section 91 of each chain link 81.

[0084] Each excavating claw 115 comprises a base 117 mounted on the peripheral face 105 of the respective leading link section 91 and a plurality of excavating fingers 119 extending from the base 117.

[0085] The base 117 presents a contact face 121 transverse to the longitudinal extent of the endless chain structure 61. The contact face 121 is forwardly facing with respect to the direction of travel of the endless chain structure 61 about the circuitous path 63. With this arrangement, the contact face 121 presents a confronting surface for pushing ballast material in its path during the excavation process, as will be explained later.

[0086] The excavating fingers 119 extend forwardly and outwardly from the base 117 in the direction of travel of the endless chain structure 61. Each excavating finger 119 has an outer end section configured as a point 123 for penetrating the ballast material.

[0087] In the undercutter portion 57, the chain structure 61 is oriented such that the chain face 111 is substantially vertical and the excavating claws 115 extend outwardly therefrom.

[0088] With this arrangement, the circulating endless chain structure 61 can cut into the central section 21 of the ballast bed 13, with the excavating fingers 119 drawing ballast materials towards the chain face 111. On the return run 69 of the endless chain structure 61 , the contact face 121 pushes ballast material out of the central section 21 of the ballast bed 13. The excavating tools 113 not only excavate ballast material from the ballast bed 13 but they also move the excavated ballast material towards, and onto, the conveying portion 59.

[0089] In the undercutter portion 57, the endless chain structure 61 travels generally along a horizontal plane; that is both the entry and return runs 67, 69 within the circuitous path 63 are generally horizontal.

[0090] The conveying portion 59 is inclined in order to carry the excavated ballast material upwardly to the elevated discharge zone 71.

[0091] In moving between the undercutter portion 57 and the conveying portion 59, the endless chain structure 61 passes through a turn section 126 around sprocket 64a (see Figure 22).

[0092] Within the conveying portion 59, the endless chain structure 61 has an ascending run 128 and a descending run 129. The ascending run 128 extends from the return run 65, with the transition therebetween being at a path section 63a of the circuitous path 63 around sprocket 64a at a turn section 126. Similarly, the descending run 129 leads to the entry run 67, with the transition therebetween being at a spiral path section 63b of the circuitous path 63 at a turn section 127 around sprocket 64b, as also shown in Figure 22. The construction of the chain structure 61 involving the series of first, second and third axes facilitates movement through the spiral path at sprocket 64b.

[0093] The conveying portion 59 comprises a trough 130 along which the ascending run 128 of the endless chain structure 61 travels between an entry end 130a and a discharge end 130b. The discharge zone 71 is at the discharge end 130b of the trough 130.

[0094] The trough 130 comprises two longitudinal side portions 131a, 131b which are spaced apart to define an elongate space 133, a base 135 and a top 137 which can be opened to provide access to the space 134. In this preferred embodiment, the top 137 a flexible strip 138 (such as a strip of rubber material) attached along one longitudinal edge thereof to one of the side portions 131. The ascending run 128 of the endless chain structure 61 is adapted to travel along the elongate space 133 in a manner such that the contact faces 121 of the various excavating tools 1 13 serve to push the excavated ballast material upwardly along the conveying portion 59 to the elevated discharge zone 71. This is best seen in Figure 26, in which the top 137 has been lifted to reveal the endless chain structure 61 travelling along the elongate space 133 to push the excavated ballast material upwardly along the trough 130. As can be seen in Figure 26, the excavated ballast material is confined in the trough 130 between the chain face 1 1 1 and the opposed longitudinal side portions 131a, with contact faces 121 of the excavating tools 113 pushing the excavated ballast material along the trough.

[0095] The entry end 130a of the trough 130 is configured to receive ballast material excavated by the undercutter portion 57. The return run 69 of the endless chain structure 61 moves the excavated ballast material towards, and onto, the conveying portion 59 at the entry end 130a of the trough 130.

[0096] The frame structure 33 includes a rail lifting mechanism 140 for lifting and supporting the section of the railway track 15 at the location where ballast material is being excavated. The rail lifting mechanism 140 may be of known kind.

[0097] In the arrangement shown, the rail lifting mechanism 140 comprises two lifting structures 141 each adapted to engage one of the railway lines 17. Each lifting structure 141 comprises a carriage 143 comprising two carriage parts 145 pivotally movable between engaging and release conditions on opposed side of the respective railway line 17. Each two carriage part 145 comprises a body 147 and two engaging rollers 149. Each engaging rollers 149 comprises a roller surface 151 and a flange 153 at the bottom of the roller surface. The arrangement is such that each engaging roller 149 can engage the respective rail 18 when the carriage 143 is in the engaging condition, with the roller surface 151 in rolling contact with the adjacent side of the head of the rail and the flange 53 engaging against the underside of the head of the rail.

[0098] The rail lifting mechanism 140 further comprises an actuating mechanism 155 for pivotally moving the two carriage parts 145 between the engaging and release conditions on opposed side of the respective railway line 17.

[0099] The rail lifting mechanism 140 further comprises an elevating mechanism 157 for raising and lowering each carriage 143.

[00 00] With this arrangement, the elevating mechanism 157 can be actuated to lower each carriage 143 into position with the carriage parts 145 in the release condition on opposed sides of the respective rail 18. The actuating mechanism 155 can then be actuated to pivotally move the two carriage parts 145 into the engaging condition whereby the engaging rollers 149 engage the respective rail 18 on opposed side thereof. . The elevating mechanism 157 can then be actuated to lift the respective rail 18 to provide support therefor while the ballast material is being excavated. [00101] Because rail lifting mechanism 140 is in engagement with the two rails 18 through the engaging rollers 149 on opposed sides of the rails, the carriages 143 can travel along the rails 18 as the machine 10 advances along the railway track 15, with the rails 18 being progressively lifted as the machine 10 advances during a ballast excavating procedure.

[00102] The machine 10 is adapted to operate in a dual mode rail-road configuration as previously described. With this arrangement, the machine 10 can be driven onto the railway track 15 using the road wheels 43. Once the machine 10 is properly positioned on the railway track 15 and ready to commence operation, the rail wheels 41 can be moved into engagement with the railway lines 17 to facilitate mobility of the machine 10 along the railway track 15 without the need for steering control as is required with mobility via the road wheels 43.

[00103] As previously mentioned, operation of the machine 10 is particularly suitable for long stretches of railway track with simple track layout configurations. This mode involves the access to the ballast bed 13 for the two undercutter portions 57 simultaneously from both sides of the ballast bed. For this mode of operation, the undercutter portions 57 are oriented to extend inwardly in an offset and overlapping relation, as depicted in the drawings/photographs. The overlapping arrangement ensures that the entire central section 21 of the ballast bed 13 is exposed to the excavation and the offsetting arrangement ensures that the two undercutter portions 57 do not interfere with each other.

[00104] It is a feature of the ballast excavating machine 10 according to the preferred embodiment that it can be used for "spot" maintenance of a section of railway track. Specifically, the machine 10 can be driven to the location where the maintenance is required and onto the railway track 15 using the road wheels 43. Once the machine 10 is properly positioned on the railway track 15 and ready to commence operation, the railway wheels 41 can be moved into engagement with the railway lines 17 to facilitate mobility of the machine 10 along the railway track 15 to perform the "spot" maintenance operation. [00105] It should be appreciated that the scope of the invention is not limited to the scope of the preferred embodiment described. By way of example, the excavating and conveying assembly 55 may be employed in other ballast excavating arrangements and is not necessarily limited to the ballast excavating machine 10 according to the preferred embodiment described and illustrated. Similarly, the chain structure 61 is not necessarily limited to either the excavating and conveying assembly 55 or the ballast excavating machine 0 according to the preferred embodiment described and illustrated.

[00106] Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.