This invention relates to propulsion apparatus for trenching or trench excavating apparatus wherein a deep trench is dug and corners are formed, the trench to receive poured concrete as in the formation of an in ground retaining wall.
Propulsion apparatus which is engageable with the side or base walls of a trench is known, and may be used to provide propulsive force within the trench, enabling a relatively light machine to be used for a particular trenching operation. Such propulsion apparatus may have difficulty adapting to varying ground types and may jam due to the ingress of dirt dislodged during the excavation process, or wet concrete, which is often poured immediately behind the trenching arm to minimise the probability of trench collapse in soft ground conditions.
The prior art discloses endless chain excavators together with mobile concrete forms mounted behind the excavator. It is intended that the excavator continuously dig a trench and while the trench is being dug, concrete is poured behind the excavator into the form carried by the excavator. The upper end of the excavator is mounted on a tractor that moves along the ground carrying the excavator with it.
In digging trenches and pouring concrete for retaining walls, it is important for the excavator to maintain a vertical attitude and for the assembly to dig itself into the ground to the proper depth in a vertical attitude. In this way proper corners can be formed.
When excavating a trench that is of considerable depth relative to the length and width of the excavator, it is extremely difficult to move the lower end of the excavator at the same pace as the tractor which carries the upper end. Hence, it is difficult, if not impossible, to maintain the required vertical attitude of the excavator without adding costly and heavy bracing structure between the tractor and excavator.
The specification of GB-A-1372467 discloses apparatus utilizing a supporting foot adapted to resist the considerable downward forces generated by a trenching chain excavator which tends to drive the chain deeper and tip the vehicle. The apparatus is not adapted to advance the lower end of the elongate trenching arm and thus overcome the torsional loads which would be inflicted on the tractor supporting an elongate trenching arm as described above in failing to maintain the required vertical attitude.
US-A-2360316 discloses the use of excavation apparatus which is driven from the base of the apparatus, but this apparatus cannot dig trenches below the level of its tractor and is in any case braced across its excavating chain assembly.
AU-B-41139/85 discloses a trenching arm assembly including a digging device adapted to provide the trenching arm with the ability to dig downward to commence a trench. However, the trenching arm in general and the digging means in particular does not provide propulsion apparatus adapted to prevent the translation of torsional loads to the tractor or resist the trenching arm from straying from its desirable orientation under such loads.
It is an object of the present invention to alleviate the above and other disadvantages and to provide improved propulsion apparatus for trenching apparatus and methods of forming in ground retaining walls which will be reliable and efficient in operation.
In one aspect, this invention resides broadly in trenching arm propulsion apparatus for excavators of the type comprising a tractor (111) supporting an upper portion of an elongate trenching arm (114) which extends to a trench depth and is advanceable by said tractor to form a trench (117), a lower portion of said trenching arm remote from said tractor being provided with propulsion means (121) engageable with a trench wall and cooperable therewith to drive said lower portion of said trenching arm in the direction of the advancing trench, characterised in that said propulsion means comprises a combined digging and propulsion assembly mounted on the lower end of the trenching arm assembly such that the trenching arm assembly may dig itself into the ground in a substantially vertical attitude.
Preferably, the tractor comprises a vehicle adapted to move along the ground on crawler tracks. The tractor preferably mounts a trenching arm comprising an endless chain excavator assembly mounted to the tractor for vertical movement relative to the tractor. Preferably, the arrangement of the tractor and trenching arm assembly includes a U-section concrete form extending vertically along the rear face of the trenching arm assembly. The trenching arm is preferably selected from trenching arms having digging means associated with a lower portion of the trenching arm and conferring thereon the ability to commence a trench by digging substantially vertically down from ground level to a trenching depth.
The propulsion means may take the form of track means, endless belt, drive wheel means or a propulsion foot assembly associated with the lower portion of the trenching arm. The propulsion means may include a flat or curved plate engageable frictionally with said trench wall, or there may be provided propulsion plate inclination means whereby the propulsion plate may be moved between an engagement-drive attitude substantially normal to said trench wall and a frictional-drive attitude substantially parallel to said trench wall. Preferably, the propulsion means comprises a combined digging means and propulsion means assembly mounted on the lower end of the trenching arm assembly such that the trenching arm assembly may dig itself into the ground in a substantially vertical attitude.
Preferably, the propulsion means is powered by drive means deriving energy from the tractor assembly, such as by way of hydraulic drive. In the case of the preferred combined digging means and propulsion means, this may comprise a digging and propulsion assembly including a drive system selected to impart digging motion to a digging element during the digging operation and to provide a propulsion imparting motion to the element during the trench excavating operation. Preferably, the digging and propulsion assembly includes means for thrusting the element downwardly into the base wall of the trench so as to support a portion of the weight of the excavator such that a the propulsion element may get a good grip upon the base wall of the trench. For example, a foot may be mounted at the end of the trenching arm and be operable by a linkage and a propulsion ram to impart a propulsion motion to the foot. A vertical loading ram may be provided to lift the foot as it steps forward and to press the foot down so that it takes part of the weight of the excavator.
Accordingly, there may be provided excavation apparatus having a tractor mounting a vertical endless chain excavator, a form assembly for concrete extending vertically behind the excavator, and an elongated foot mounted at the lower end of the form, characterised in that said elongated foot is operable by foot rotation means for swinging said foot back and forth in a vertical attitude for digging the excavator and form assembly into the ground to commence a trench, by foot displacement means for moving said foot back and forth in a horizontal attitude to drive a lower portion of said vertical endless chain excavator in the direction of the advancing trench, and by preloading means acting on the foot for applying at least a portion of the weight of said excavator onto said foot.
The propulsion means may include a propulsion member, preload apparatus adapted for urging said propulsion member against said trench wall, and drive apparatus for driving the trenching arm forward along the trench relative to said propulsion member from a starting position adjacent said propulsion member.
If required, the propulsion means may also include retraction apparatus for withdrawing the propulsion means into a stowed position free of operative contact with the trench wall or reverse drive apparatus for drawing the propulsion means forward to its starting position, such that the propulsion means may be operated in reciprocating motion for imparting discontinuous forward motion to the trenching arm.
The preload apparatus may include an actuator of any type such as a rotary or linear electric actuator. It is preferred, however, that the preload apparatus include a linear hydraulic preload actuator, and that the preload actuator be a reversible or double-acting type, such that it may also operate the retraction apparatus; although the latter may be operated by an independent hydraulic retraction actuator if desired.
The propulsion apparatus may be attached to the trenching arm by slides along which the propulsion member may be driven by the preload actuator. The latter may be controlled to provide any desired preload function, but it is preferred that the preload actuator be controlled to maintain a substantially constant level of preload during operative movement of the propulsion member such that a substantially constant tractive effort may be obtainable therefrom.
Preferably, the drive means of the apparatus includes a double-acting propulsion actuator for operating the drive means and reverse for reduced component count, although separate actuators may be used if desired. A positioning actuator may also be provided and may be adapted to interact with the propulsion actuator such that the displacement of the propulsion member relative to the trenching arm along and normal to the trench wall may be controlled to any desired configuration by actuator control means. For instance, the actuator control means may control the propulsion and positioning actuators to hold the propulsion member at a desired attitude relative to the wall while it is extended relative to the trenching arm, and may then control the preload actuator to withdraw the propulsion member from the wall before returning it to a position adjacent the trenching arm.
The actuator control means may also be adapted for control of the preload, propulsion and positioning actuators for operation of the propulsion member in an excavating mode for cooperating with the trenching arm to excavate a starting slot for a trench, and in a propulsion mode for urging the trenching arm forward within a trench. Actuator travel sensing means may be provided for feedback of propulsion member position and attitude, whereby the control means may be provided with feedback signals.
Where the propulsion means comprises a track type apparatus, the propulsion means may include a propulsion element frame, a continuous propulsion element movable about said propulsion element frame and having an endless propulsion surface engageable between said propulsion element frame and said trench wall, preload apparatus connected between the trenching arm and said propulsion support frame for urging said propulsion element into engagement with said trench wall, and drive apparatus for moving said continuous propulsion element about said propulsion element frame.
The continuous propulsion element may be divided transversely into a plurality of propulsion segments between which support means for the propulsion element frame may pass. The propulsion segments may be provided with extendible cutter apparatus moveable between an extended position in which material may be cut from outside or between the propulsion segments and a stowed position in which the cutter apparatus is confined within the axial boundaries of the propulsion segments such that material may be excavated adjacent the support means.
The drive means may be formed to drive the propulsion means in a reverse drive mode to function as a supplementary excavation device for cooperating with the trenching arm to excavate a starting slot from which the trench may be cut.
Where the propulsion means includes an endless belt, it may be segmented transversely into belt segments whose travel paths away from said trench wall diverge to form a transverse aperture through which support means for said propulsion element frame may pass.
The endless belt may include a plurality of chain links pivoted together along transverse pivot axes, each said chain link including a front link face and a rear link face adapted for operative sealing engagement with respective rear and front link faces on adjacent ones of said links over a range of angles of articulation between adjacent ones of said links about said pivot axes such that operative sealing is maintained between adjacent links during passage of the chain apparatus about a sprocket.
Suitably, the front and rear link faces are formed of part-cylindrical portions having their cylinder axes substantially coincident with respective pivot axes, whereby they may pivot cooperatively such that operative sealing is maintained therebetween.
In another aspect, this invention resides in a method of cutting a trench using an excavator of the type comprising a tractor supporting an upper portion of an elongate trenching arm which extends to a trench depth and is advanceable by said tractor to form a trench, a lower portion of said trenching arm remote from said tractor being provided with propulsion means engageable with a trench wall and cooperable therewith to drive said lower portion of said trenching arm in the direction of the advancing trench, the method including the steps of inserting said elongate trenching arm into the trench, engaging a trench wall with said propulsion means and operating said propulsion means to advance said lower portion in concert with said tractor to advance said trenching arm.
In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, wherein:-
The propulsion apparatus 10 shown in FIGS. 1 to 9 is enclosed in a housing 11 slidably attached to the rear face of a trenching arm 12 along slides 13. The housing 11 is moveable along the trenching arm 12 by a preloading actuator 14 attached to the trenching arm 13 by a pair of interlocking racks 15 which may be adjusted to obtain the desired range of movement for the housing 11 relative to the base of the trenching arm 12.
Within the housing 11 is a hydraulic positioning actuator 16, the operating rod 17 of which extends through a slide 20 and rod seals 21 attached to the base of the housing 11. The propulsion foot 22 is pivoted to the base of a foot carrier 23 by a foot pivot 24, and the foot carrier 23 in turn has an upper front pivot 25 connected direct to the housing 11 and an upper rear pivot 26, which is connected to the housing 11 through a propulsion actuator 27. A crank arm 30 formed on the rear of the propulsion foot 22 is connected to the operating rod 17 through a link 31. A flexible boot 28 surrounds the lower end of the propulsion actuator 27 to prevent the ingress of dirt or wet concrete into the housing 11.
An endless digging chain 33 passes around the trenching arm 12 and may be utilised for excavating a slot beneath itself when excavating a vertical starting slot for a trench or for excavating a trench in front of itself when forming the trench.
As shown in FIGS. 2 to 5, the trenching arm 12 is operable to excavate a vertical starting slot beneath itself to position itself for the excavation of a trench. During this phase of the trenching operation, the propulsion foot 22 is operated in a slot excavation cycle to scrape material 32 from beneath the propulsion apparatus 10 and deposit it adjacent the trenching arm 12 where it may be picked up by the trenching chain and drawn to the surface for disposal. Firstly, the foot 22 is moved into a raised horizontal position by retraction of the positioning actuator 16 and the preloading actuator 14, as shown in FIG. 2. The foot 22 is then forced downward into the material 32 by extension of the preloading actuator 14, as shown in FIG. 3. While engaged within the material 32, the foot 22 is then swung in an arc of approximately ninety degrees about the foot pivot 24, as shown in FIG. 4, shearing material 32 from beneath the propulsion apparatus 10 and depositing it adjacent the trenching arm 12, from where the digging chain 33 conveys it around the front of the trenching arm 12 to the surface of the ground. The preloading actuator 14 is then retracted to raise the foot 22 clear of the material 32, as shown in FIG. 5, after which the foot 22 is swung back into the horizontal position in which it began the cycle.
Referring now to FIGS. 6 to 9, it will be seen that, when the trenching arm 12 has reached the desired depth for the excavation, the propulsion foot 22 may be operated in a propulsion cycle to force the trenching arm 12 forward into the advancing face of the trench. At the beginning of a propulsion cycle, as shown in FIG. 6, the foot 22 is held in a raised horizontal position with the preloading actuator 14 and the positioning actuator 16 in their retracted positions. Referring now to FIG. 7, the preloading actuator is then extended until the foot 22 is engaged with the base wall 34 of the trench with the desired level of preload applied to it. This preload may be controlled to any desired value, but it is preferred that it attain a significant portion of the weight of the trenching arm 12 and the trenching machine supporting it, whereby significant longitudinal drive force may be generated by the propulsion apparatus 10. The propulsion actuator 27 is then retracted, rotating the foot carrier 23 about the upper front pivot 25 such that the foot 22 is forced rearward relative to the housing 11, as shown in FIG. 8, urging the trenching arm 12 forward. The foot carrier 23 and the link 31 form a linkage which maintains the foot 22 in a substantially horizontal attitude during this phase of the cycle. When the foot 22 has reached the limit of its rearward travel relative to the trenching arm 12, the preloading actuator 14 is retracted, as shown in FIG. 9, raising the foot 22 away from the base wall 34, after which extension of the propulsion actuator 27 drives the foot carrier 23 and the attached foot 22 forward into its starting position.
If the ground conditions are deemed to be unsuitable for force transfer by frictional contact between the foot 22 and the base wall 34, such as in the case of wet clay, the positioning actuator 16 may be extended sufficiently to rotate the foot 22 into a substantially vertical position such that it may embed itself into the base wall 34 to provide the necessary force transfer.
The wheel-type propulsion apparatus 40 shown in FIG. 10 has a support arm 41 pivoted to a support frame 42 attached to a trenching arm 43. A radial-piston hydraulic motor 44 of the rotating-casing type has its shaft bolted to the outer end of the support arm 41, and a wheel rim 45 with cleats 46 is attached around the motor casing 47. A preload actuator 50 extends between the support arm 41 and the support frame 42 to permit the wheel rim 45 to be forced against the base of the trench 51.
The propulsion apparatus 40 may be operated to propel the trenching arm 43 along the trench 51 by rotating the wheel rim 45 forward at the top at a slow rate comparable to the advance rate of the trenching arm 43. Where it is necessary to excavate a slot at the start of a trench 51, the wheel rim 45 may be rotated backwards at higher speed such that the cleats 46 may scrape material from beneath the wheel rim 45 and deliver it to the trenching arm 43 for transport to the surface.
The chain-type propulsion apparatus 60 shown in FIGS. 11 to 14 has a housing 61 which is attached through slides 62 to a trenching arm 63. A chain assembly 64 is attached to the lower end of the housing 61 and comprises a chain frame 65 about which a central chain 66 and outer chains 67 pass. The central chain 66 passes over front sprocket assembly 70 and rear sprocket 71, while the outer chains 67 also pass over upper sprocket assembly 72. The chain frame 65 is connected to the housing 61 via a bifurcated support 73 which passes between the upper portions of the central and outer chains 66 and 67. Roller chains 74 and 75 provide drive from hydraulic motors 76 and 77 to the upper sprocket assembly 72. The roller chain 74 from the upper hydraulic motor 76 passes around idlers 80 to clear the lower hydraulic motor 77.
The chains 66 and 67 comprise links 81 formed with complementary front and rear faces 82 and 83 respectively which slide relative to one another as the links 81 pass around a sprocket such that no significant passages open up for the ingress of dirt or wet concrete. Face seals 85 attached to the chain frame 65 engage with recessed side faces 86 on the links 81 to minimise ingress of dirt or wet concrete through these gaps.
The propulsion apparatus 60 may be operated to propel the trenching arm 63 along a trench by driving the chains 66 and 67 forward at the top at a slow rate comparable to the advance rate of the trenching arm 63. Where it is necessary to excavate a slot at the start of a trench, the chains 66 and 67 may be driven backwards at higher speed such that the cleats 87 may scrape material from beneath the chains 66 and 67 and deliver it to the trenching arm 63 for transport to the surface.
Referring now to FIGS. 15 and 16, it will be seen that the propulsion apparatus 90 is similar to the propulsion apparatus 60, but has a single hydraulic drive motor 91 mounted with its axis vertical and driving a primary drive sprocket 92 through a crown wheel 93 and pinion 94. A roller chain 95 carries the drive from the primary drive sprocket 92 to the primary driven sprocket 93, and the latter comprises part of the upper sprocket assembly 96 which in turn drives the outer chains 97. A thrust actuator 100 mounted between the propulsion frame 101 and the trencher arm 102 permits a desired preload to be applied between the trench wall 103 and the chains 97 and 104. Seal plates 105 extend between the side faces of the sprockets 92 and 93 to seal the crown wheel enclosure 106 from the ingress of dirt or concrete from the chains 97 and 104.
The excavator apparatus 110 shown in FIG. 17 comprises a tractor 111 which may move along the ground 112 on crawler tracks 113. An endless chain excavator assembly 114 is mounted to the tractor 111 for vertical movement relative to the tractor 111, and carries an endless digging chain 115 which may excavate the advancing face 116 of a trench 117. A U-section concrete form 120 extends vertically along the rear face of the excavator assembly 114, and a combined vertical digger and forward propulsion unit 121 is mounted on the lower end of the concrete form 120. Hydraulic power for the operation of the vertical digger and forward propulsion unit 121 is supplied by a hydraulic power pack 122 mounted on the tractor 111, and operation of the vertical digger and forward propulsion unit 121 is controlled by a solenoid assembly 123 under the control of a control computer 124. The hydraulic power pack 122 also provides power to drive the crawler tracks 113 and the digging chain 115.
To form an in ground wall, the excavator apparatus 110 is positioned above the starting point for the wall with the excavator assembly 114 in a raised position fully above the ground 112. The digging chain 115 is energised, and the vertical digger and forward propulsion unit 121 is operated by the control computer 124 in its vertical digging mode. The excavator assembly is then lowered into the ground, and the digging chain 115 and the vertical digger and forward propulsion unit 121 combine to excavate a starting slot for the trench 117. When the starting slot has reached the desired depth, the crawler tracks 113 are energised for forward motion, and the control computer 124 is switched to control the vertical digger and forward propulsion unit 121 in a forward propulsion mode, urging the digging chain 115 forward against the advancing face 116 of the trench 117.
Concrete is poured into the trench 117 behind the concrete form 120 to form an in ground wall 125.
The advantages of the present invention are that it becomes possible to dig straight down with the excavator and accessory equipment, such as a concrete form, and when the desired depth has been obtained to proceed forward, digging a trench, with the excavator maintained in a vertical attitude. At a corner, the excavator is raised, is shifted to the proper angle to form the corner and is driven straight down to begin the excavation of the adjacent wall.