Background of the Invention In the construction of roads, housing or apartment complexes and other infrastructures, it is known to cut trenches in the ground to receive pipes, electrical cables, telecommunication lines and the like. In the case of roads, drainage pipes are provided to run alongside at least one side of the road underneath but close to the surface. To this end, a relatively narrow trench to accommodate the pipe is dug out and after installation of the pipeline re-filled.

For this purpose it is known to use specialised stone cutting circular saws mounted on vehicles custom made for such tasks. One such piece of equipment is known as a Hydra Saw manufactured in Queensland, Australia. A self-propelled, rubber tyred tractor has mounted at its rear a saw blade hood or housing. A circular earth/stone cutting saw blade is driven about a substantially horizontally extending axis. The circular saw blade is arranged and mounted such that the blade can be moved along a substantially vertical extending axis only to lower and raise the saw blade to adjust the depth of cut of the trench. The housing encapsulates an upper part of the saw blade and a lower part of the saw blade protrudes downwards to engage and cut into the ground. During the cutting operation, a considerable amount of debris is propelled directly in a rearward direction into the trench which has just been cut and part of the debris is propelled into the housing around the saw to be expelled in front of the saw in the trench digging path. While such a specialised and custom made trench digging vehicle may be justifiable from an operational and economic point of view for major projects, where the costs of the machinery can be offset during the entire

project life, the economic viability becomes less attractive where such a machine is used on small scale projects and machine down-times are high. Of greater significance, however, is that known trench digging machinery with circular saw blades, while being able to effectively cut a trench, are not efficient in the removal of the cut-away debris from the trench, thus necessitating a subsequent cleaning up of the trench by other means or equipment, prior to being ready for receiving the conduits to be embedded in such a trench. This adversely affects the overall efficiency and costs of the trench digging operation. Also, the advance or cut-rate achievable is limited by the speed with which debris can be expelled from the housing to avoid jamming of the circular saw blade within the housing cavity. A further disadvantage is the limited manoeuvrability of the trench digging saw due to its mounting on the vehicle.

Summary of the Invention It would be advantageous if at least preferred embodiments of the present invention addressed these drawbacks. It would also be advantageous if at least

^• preferred embodiments provided a trench digging saw which is extremely versatile in use and adaptable to different operational conditions.

In a broad aspect thereof, the present invention provides a trench digging saw comprising a circular saw blade driven about a first axis. A housing can partly encircle and cover the periphery and sides of the saw blade such that the blade protrudes from a first opening in the housing. The blade can then engage a working surface to cut a trench along a predetermined path. The housing can be adapted for mounting at an outer end of an arm-linkage assembly on a vehicle such as to be positionable thereby and held in fixed relationship with respect to the vehicle and the working surface plane. A main discharge opening can be provided to expel debris cut by the saw blade from the housing. Optionally, a

means for directing debris not discharged through the main discharge opening can be provided to expel such debris through the first opening behind the saw blade. Then a means for collecting and directing such debris expelled through the first opening towards the saw blade can be provided so that such debris is re-propelled by the saw blade towards the main discharge opening. Optionally, a means for directing debris discharged through the main opening away from the trench cutting path in front of the saw can also be provided.

In one preferred embodiment thereof, the present invention can further provide a trench digging saw adapted for detachable mounting on an outer end of an arm-linkage assembly of a self-propelled vehicle, such as an excavator or rubber tyred tractor, the saw comprising: a circular saw blade having a plurality of cutters or teeth spaced from one another and arranged along the periphery of the blade, the saw blade being adapted for being driven about a first axis by a motor; a housing defining a cavity and having a first opening, the saw blade being received within the cavity and so as to protrude from the first opening for engagement of a working surface in use to cut a trench therein, and having a discharge opening for discharging from the housing debris cut by the saw blade and that has been conveyed into the housing cavity; an attachment head associated with the housing, the attachment head being mountable at the outer end of the arm-linkage assembly for controlled positioning with respect to the working surface; a drag plate associated with the housing, and arranged at the rearward end of the housing for extension substantially in the same plane as the saw blade but in the vicinity of the first opening such that a lower end thereof is spaced approximately the same distance from the housing as the lowest extent of the saw blade cutters; and a screw conveyor arranged externally at a forward

end of the housing in the vicinity of the discharge opening, the screw conveyor extending laterally greater than the thickness of the saw blade and being positioned for activation about a second axis intersecting the saw blade plane, thereby conveying debris discharged from the discharge opening away from the saw trenching path.

Preferably, the main discharge opening is positioned at a forward end of the housing in the vicinity of the location where, in use, the saw blade cuts the trench. Such an arrangement ensures that most of the debris cut by the saw will be expelled through the discharge opening by the centrifugal forces created by the rotating blade without having to travel along a substantial distance within the housing. The cavity in the housing is preferably shaped to generally correspond to the contour of the blade but leaving a radial gap between the cavity inner surface and cutters of the saw blade. This allows debris (optionally including debris trapped between adjoining cutters) and not expelled from the main discharge opening to travel along the gap towards the rear of the housing for discharge through the first opening in a downward direction into the trench behind the saw blade. As the trench digging saw is moved forward along the trench digging path, the debris discharged behind the saw blade is pushed forward by the drag plate. This debris will thus be brought in contact with the rotating saw blade again and conveyed to the main discharge opening for expulsion therethrough.

Advantageously, the housing includes a discharge chute at least partly surrounding the discharge opening, the chute having deflection means arranged such that at least part of the debris cut away and propelled by the saw blade in a radially outward direction in the plane of the saw is deflected by the deflection means laterally out of this plane and generally sideways from the housing.

Preferably, the screw conveyor comprises an auger having an axis of rotation inclined with respect to the

plane in which the saw is arranged, as well as being inclined to the first axis of the saw. The debris discharged in front of the trench digging saw will thus be conveyed in an inclined rearward direction laterally from the housing upon advance of the saw along the trenching path.

Advantageously, a scraping plate cooperates with the auger of the screw conveyor to scrape the surface in front of the trench digging saw, thereby providing a substantially planar working surface to the saw in use. The auger is advantageously driven by a hydraulic motor which is supplied with hydraulic fluid from the vehicle carrying the saw; similarly, the drive for the saw blade is preferably a hydraulic motor fed from the main hydraulic circuit of the self-propelled vehicle.

The diameter of the saw blade may advantageously range from about 600mm to 6m and have a width allowing cuts of about 50mm to about 400mm width. Digging depth can accordingly range from about 100mm to about 2.8m. A number of advantages of the inventive trench digging saw are that the saw can work through 360 ^° rotation about a vertical axis without requiring re-positioning of the vehicle, since the saw is mounted on the linkage arm assembly. It is possible to saw along steep embankments or even vertical surfaces since the saw mounting allows pivoting of the housing about a horizontal axis. It is also possible to cut trenches under water by disposing the excavator on a barge and mounting the saw to the free end of the arm linkage assembly of the excavator. Thus, lying of submarine cables is facilitated.

In another aspect an improved trench digging or stone cutting saw blade is provided which comprises: a circular saw disk; a plurality of cutting tools each having a tool carrier and a cutting bit, the cutting tools being removably fixed in a sequence around an outer-peripheral face of the saw disk to protrude radially as well as laterally from a side face of the disk, each tool carrier

protruding laterally a first amount from a respective side face opposite from which the respective cutting bit protrudes, and each two adjacent cutting tools having their cutting bits arranged to protrude from opposite side faces; and at least two annular wear protection sections, one each extending near the peripheral face from a respective one of the side faces and having a thickness in the lateral direction that is greater than the first amount. Preferably, the annular wear protection sections are provided by a ring-shaped integral plate, or by discrete plate sections forming a continuous or discontinuous ring. In particular, the annular wear protection sections may be formed of a plurality of discrete, narrow platelets arranged to form a circle, the platelets being arc-shaped in plan view and rectangular or trapezoid in cross-section and abutting endwise against one another to form a continuous circle when positioned on the saw disk. Alternatively, the annular wear protection sections may be formed from a plurality of discrete platelets arranged to form a regular polygon around the disk, the platelets having a rectangular or trapezoid cross-section, and being shaped in plan view in the form of regular trapeziae that abut endwise against one another to form a closed polygon. The platelets may alternatively be arranged such as to leave gaps between them, thus providing a discontinuous wear plate surface.

Advantageously, the wear plate or wear platelets may be welded to the side faces of the saw disk. The wear plate/platelets may be comprised of two or more stacked plate elements of rectangular cross-section, whereby the plate element which abuts against the side face is preferably made of a mild steel for ease of welding onto the steel saw disk, and the outer plate element, which provides the actual wear resistance and protection for the cutting tool carrier portions which protrude from the side faces, being made of an abrasive resistant stainless steel, i.e. tungsten or molybdenum carbide steel.

Typically, the discrete platelets may have a dimension of 400-500mτn in length, 100-200mm in width, and 20-40mm in thickness, which may vary depending on the diameter of the saw disk and amount by which the tool carrier base portions protrude from the side faces. The wear plates/platelets should preferably be arranged as close as possible to the outer periphery of the saw disk next to the base portions of the tool carriers, i.e. 25mm from the outer perimeter edge, to provide optimum wear protection.

The above described saw disk with wear plates on both side faces increases the life-time of the saw blade by a factor of about 4 as compared to ordinary saw blades without such wear plates. It is to be further noted that the annular guide plates also act as a self-centering guide for the saw blade during cutting of trenches and cutting operations into sandstone by increasing in-plane stiffness against bending of the blade in reaction to lateral reaction loads during cutting. Also, and in contrast to a radially extending arrangement of wear plates, which tend to act as scrapers and not to provide optimum protection for the base portions for the cutting tool carriers, the annular arrangement of the wear plates provide skid plates along the widthwise cut face rather than grate plates.

Brief Description of the Drawings The invention will be better understood from the following non-limiting description of a preferred embodiment of the invention given with reference to the accompanying drawings, in which:

Figure 1 is a perspective schematised view showing a trench digging saw according to the present invention.

Figure 2 is a side view in direction of arrow II of Figure 1 of the trench digging saw. Figure 3 is a top view of the trench digging saw of Figures 1 and 2.

Figure 4 is a schematic plan view of a saw blade which can be used with the trench digging saw of Fig.

1 - 3 .

Figure 5 is a schematic, enlarged detail view of the saw blade in direction of V in Figure 4 partly in section. Modes for Carrying out the Invention

In describing the preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "forward", "rearward", "radially", "peripherally", "upwardly", "downwardly", and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

Referring now to the drawings, in particular to Figure 1, there is shown an improved trench digging saw, generally designated by 10, which is specifically built to be pivotally connected to the free end of a linkage arm assembly of a self-propelled vehicle (not shown) . The self-propelled vehicle can be a conventional hydraulic excavator, for example, of the type comprising an undercarriage mounted on tracks, an upper structure that is rotatable about a vertical axis on the undercarriage and a linkage arm assembly comprising booms joined at knee-linkages which are manipulated in a known manner by suitable hydraulically powered jacks or motors. Of course, other types of vehicles having an arm-linkage assembly to support at its free end an earth moving tool can also be used. In the following, reference will be made to an "excavator" which encompasses all types of self-propelled vehicles. The trench digging saw 10 comprises, generally, an attachment or connector head assembly 20, a housing 40, a circular saw blade 50 with motor 30, a screw conveyor assembly 60 with motor 66 and a drag plate or sword 70 as

is described in more detail in the following.

The trench digging saw 10 can be attached to the free end of the boom of the arm-linkage assembly through the attachment or connector head, generally designated by 20, which includes a base plate member 21 and a pair of substantially parallel side plate members 22a and 22b integrally formed with or welded to and extending vertically from the base plate.

The side members 22a and 22b are spaced apart from each other by a distance enough to receive therebetween the distal end of the boom arm, generally indicated as 24 in ghost outline, of the excavator (Figure 2) . The side members 22a and 22b are also provided with two pairs of coaxially aligned seating holes to permit insertion of respective mounting pins 26a, 26b, thereby providing for pivotal attachment of the connector head 20 and thus the whole trench digging saw 10 to the boom arm 24. Tilt arm assembly members 28a, 28b, which are articulated to one another in a conventional and known manner, allow for positional adjustment of the saw 10, wherein actual pivoting is effected by means of an hydraulically powered jack, the free rod end of which is indicated at 29 and articulated at pivot 27.

Side plate 22b is provided with a receptacle hole (not shown) through which extends a drive axle of a hydraulically driven motor 30 located between the side members 22a and 22b as illustrated in Figure 3. The motor 30 is fixed and supported at side plate 22b. The hydraulic lines running to the motor 30 have been omitted for purposes of clarity; these lines are connected to the main hydraulic fluid source of the excavator in a conventional manner. This type of connector head enables the saw 10 to be easily removed from the arm-linkage of the excavator in a short time, typically about 5 min, so that the excavator is capable of being refitted with another tool/implement to carry out other tasks.

Disposed beneath the connector head 20 is a support beam 32 which is welded to the base plate, the connector

head 20 being arranged to extend laterally from the support beam 32.

The saw blade housing, generally indicated at 40, has an overall half circular configuration and is relatively narrow laterally compared to the diameter of the housing 40. The housing 40 is made up of two side plates 42a, 42b extending parallel to one another and bridged at their upper half circular edges by an arc- shaped hood plate 43. Support beam 32 is welded to the lower terminal edge of the side plate 42A, whereas a further support beam 33, which extends in parallel to the first beam 32, is welded to the lower terminal edge of side plate 42b. As can be appreciated from Figure 3, though not specifically illustrated, side plate 42a has an opening through which the drive axle of motor 30 protrudes into the housing cavity (that is defined between plates 42a, 42b and 43) .

The housing is made up of steel sheets welded together to provide the form illustrated in Figure 2, whereby the forward end of the half circular housing is removed and provides a discharge opening in a forward facing direction onto which is welded a discharge chute, generally indicated at 44, comprised of a number of deflection plates in a manner which will become clearer below.

Within the housing 40 is arranged the trench digging saw blade 50, having a hub into which is received the drive axle of motor 30 such that the blade 50 rotates about axis A (which generally extends in a horizontal plane and perpendicular to the saw blade plane B) . The circular saw blade 50 comprises a saw disc 52 on which are mounted in known manner a plurality of teeth or cutter holders, each carrying a cutter or tooth, only schematically illustrated at 54, which are spaced from one another at regular intervals along the periphery of the saw disc 52. As can be further seen in Figure 2, the housing only surrounds an upper part of the saw blade, a lower part protruding therefrom through a lower

side opening of the housing 40. The saw blade 50 is received within the housing cavity such that a radial gap 56 extending along the inside of the housing is maintained between the radially outermost tips of the cutting tools 54 and the inner facing surface of the arc shaped housing plate 43.

The discharge chute 44 comprises a number of deflection plates that are welded together and arranged such that their planes are angled with respect to plane B, in which the saw blade extends. Accordingly debris cut by the saw blade and propelled in a radially outward direction with respect to axis A, when impinging on the deflector plates is imparted a motion obliquely to plane B, as will be described in more detail below. As has been noted, the trench digging saw 10 further comprises a screw conveyor assembly 60, arranged on the front side of the housing 40 in the vicinity of the discharge chute 44 and extends with its main longitudinal axis C to subtend an acute angle γ with respect to the plane B (and also subtends an acute angle with the rotation axis A) . In an alternative arrangement, the screw conveyor axis C can extend perpendicularly to plane B to be parallel to axis A.

The screw conveyor assembly includes two bearing plates, schematically illustrated at 62a, 62b, which rotatingly support the hubs of the axle 63. On this axle, spiral plate 64 of an auger 65 is mounted (welded) , so that the axle 63 and spiral plate 64 define the auger 65. A hydraulic drive 66 is coupled to one of the hubs of the axle 63 and supported at bearing plate 62b to impart rotation to the auger 65, as shown in Figure 3.

The screw conveyor assembly 60 further includes a scraping plate 67 which is arc-shaped in cross-section and which extends between and is welded onto the bearing plates 62a, 62b, and so that a lower terminal edge 68 thereof more or less coincides with the maximum radial distance of the spiral plates 64 from the axis C about which the auger 65 rotates. As can be seen in Figure 3,

a radial gap is maintained between the spiral plate 64 and the inner face of the scraping plate 67. In operation, the lower edge 68 of the scraping plate 67 is intended to glide over the ground to scrape the surface immediately in front of the trench digging saw, thus removing loose debris which is then conveyed by the auger 65 sideways and backward as indicated by arrow F, out of the intended trench digging path. Here again, the hydraulic drive motor 66 for the auger 65 is fed through hydraulic lines (not shown for clarity) which provide hydraulic fluid from the main hydraulic system of the excavator carrying the trench digging saw.

Support beams 69a and 69b are welded to the scraping plate 67 at the location of the bearing plates 62a and 62b to extend towards support beam 33 and 32, respectively, where they are welded so as to rigidly connect the screw conveyor assembly 60 to the main support beams 43 and 42.

On the rearward side of the housing 40 is located the drag plate 70 which is arranged to extend in substantially the same plane B as the saw blade 50. The drag plate 70 has a thickness which preferably corresponds to the cut width the saw blade is able to achieve. The drag plate is arranged between the two rearwardly extending ends of the support beams 42 and 43 and is fixedly attached thereto by bolts 71a and 71b. The upper bolt 71a is received in coaxially arranged holes of two parallel flanges 72a, 72b welded onto the support beams 32, 33, respectively, thus providing a rigid but removable attachment of the drag plate 70 to the support beams 32, 33.

As can be seen from Figure 2, the drag plate 70 is provided on a forward facing side with arcuate shaped wear plates 74 which maintain a gap to the cutters of the saw blade 50 similar to the gap 56 within the housing 40. The lower terminal end of the drag plate 70 is arranged to substantially coincide with the maximum distance the cutters 54 have from the axis of rotation A of the saw

bl ade 50 .

In operation, the trench digging saw is attached through the attachment head 20 to the outer or free end of the arm-linkage assembly of the excavator vehicle as illustrated in Figure 2. Hydraulic hoses are connected to the drive 30 for the saw blade as well as the hydraulic motor 66 to drive the auger 65. This combination of trench digging saw 10 with the self propelled excavator and its arm-linkage provides an extremely versatile machine which may be used to accurately cut a trench into a working surface by appropriately manipulating the linkage and fixing the position of the arms relative to one another and with respect to the undercarriage of the excavator such that linear motion of the excavator along a given path enables the cutting of a trench with the saw. The trench depth is easily adjustable by manipulation of the arm linkage, thus obviating the need for an independent drive to adjust the depth of cut of the saw. The saw blade 50 is activated so as to rotate in the direction of arrow D and the cutters 50 are brought into engagement with the ground. The hydraulic excavator is moved along the trench path while simultaneously lowering the trench digging saw 10 until the scraping plate 67 comes to abut on the ground. The debris cut out from the working face at the trench is moved in the direction of arrow D and is imparted with a centrifugal force to move on a superimposed radial-peripheral path to exit through the discharge chute 44. A generally radially directed debris impinges on the deflection plates at the chute 44 and is deflected toward the screw conveyor assembly 60 to accumulate in front thereof. The conveying motion imparted by the auger 65 subsequently moves the debris expelled from the discharge chute 44 along the direction indicated by arrow F out of the trench digging path together with debris scooped off by the semi-circular grating plate 67. Any debris not discharged through the discharge chute 44 follows an

arcuate path along the gap 56 between saw blade 50 and the inner surface of the arcuate housing plate 43 to be discharged at the rearward end into the gap between drag plate 70 and saw blade 50. As is evident, upon forward motion in direction of arrow E, debris accumulated at the lower end of the drag plate 70 is brought into engagement with the cutters 54 and is conveyed in a forward direction for subsequent discharge through chute 44. This avoids accumulation of debris in the trench in front of the drag plate as well as within the housing, thus providing an increased trenching speed without the necessity of a subsequent cleaning operation behind the trench digging saw.

Whilst the invention has been described with reference to a particular embodiment which is, therefore, illustrative only, modifications to the specific features set forth in the foregoing description will be readily apparent to those skilled in the art without departing from the scope of the invention. For example, the screw conveyor assembly 60 may be mounted through its support beams 69a, 69b to pivot with respect to the support beams 32, 33 such that the scraper plate 67 can be brought into abutment with the ground surface and secured against further pivoting, to thereby adjust for different depths of cuts the saw blade 50 may be required to follow along a trenching path.

The auger 65 may also have different spiral blades, i.e. two sections with diverging spiral paths to convey debris to both widthwise sides of the trenching path instead of one side only.

Of course other types of drive systems, i.e. electrical, can be used to drive the saw blade and the auger and it is possible to either incorporate mechanical or pneumatic or electric synchronising means, or a gear chain, if only one drive is to be used for both saw blade and auger.

Also, different types of circular saw blades adapted to earth/rock removal purposes may be employed.

For example, Figures 4-5 show a circular saw blade which can be used with the trench digging saw in accordance with the invention. However, the illustrated saw blade is also applicable to other types of saws, i.e. stone cutting saw devices such as described in AU-A 51946/93.

The saw blade 150 comprises a circular saw disc 152 made of steel having (in a known manner) a plurality of equidistantly spaced mounting slots (not illustrated) on the peripheral, curved outer face 153 of the disc 152. The slots are adapted to receive respective cutters, illustrated schematically at 154 which are removably fixed against movement in the slots (in a known manner) .

The cutters comprise (in a known manner) a tool holder or carrier 154a which supports the actual cutting tool 154b (i.e. typically a cutting chisel or bit) ; the illustration in Figure 5 is only schematical. The tool carrier 154a is mounted in the slot such as to allow individual removal and replacement of cutters when they are worn-off or damaged, thus avoiding necessity of replacing the entire saw blade.

As can be inferred from Figures 4 and 5, the cutters are arranged such as to protrude radially from the outer peripheral face 153 as well as, in alternatingly succession, are oppositely inclined with respect to the axis of rotation A of the saw blade. In other words, successive cutters are mounted such that the cutting tool 154b protrudes laterally from one of the side faces 155a, 155b of the disc 152 while a base portion of the carrier 154a protrudes laterally from the opposite side face 155b, 155a.

As can be further seen in Fig. 5, adjoining or successive cutters alternate in their direction of protrusion from a respective one of the lateral side faces 155 and 155b. Thus, the effective cutting width of the saw is greater than the thickness of the saw disc 152.

To avoid wear/abrasion of the portions of the cutter

carriers 154a which protrude beyond the planes of the side faces 155a, 155b of the saw disc 152, each side face is provided with an annular plate 157a, 157b which extends near the perimeter edge of the disc 152. In the illustrated embodiment, the annular wear plates 157a, 157b are each comprised by a plurality of plate members 158 or platelets of rectangular cross- section and shaped, in plan view, in the form of regular trapeziae. The platelets 158 abut with their shorter sides one against the other to form a regular polygon encircled by the perimeter edge of the disc 152 as illustrated in Fig. 4. The platelets 158 are welded to the steel saw disc side faces 155a, 155b and consist of a base section 159a of mild steel which carries a wear resistant outer face section 159b of e.g. tungsten or molybdenum carbide steel. The thickness of the wear platelets is chosen to be greater than the amount the base of the tool carriers 154a protrude from the respective side face 155a or 155b of the saw disc 152, but smaller than the amount the cutting tools protrude from the opposite side face 155a, 155a.

A typical thickness for the wear plate/platelets would be 20 to 30mm. The wear plates 157a, 157b, apart from providing wear protection for the tool carriers 154a also act as guides during a cutting operation since they increase bending stiffness of the saw disc. The platelets 158 can also be arranged such as to leave radially extending gaps between neighbouring platelets such as to avoid debris entrapment between the lateral cut faces of the trench and the side faces of the saw blade.