Abstract:
The invention concerns a levelling device ( 10 ) for an impact roller of the type having at least one out-of-round compactor mass which, when caused to traverse a soil surface, applies periodic compacting blows to that surface. The levelling device of the invention is coupled to the impact roller so as to trail behind the impact roller. It includes a support frame ( 36 ) and, for each compactor mass of the impact roller, a ground-engaging levelling blade ( 52 ) fast with the support frame. The levelling blade is arranged to cut soil which has been traversed by the compactor mass and thereby to perform a soil levelling action. A ground-engaging shoe ( 58 ), one for each levelling blade, is connected to the support frame for pivotal movement about an axis transverse to the direction of movement of the impact roller The shoe serves to control the depth of cut achieved by the levelling blade.

Description:
This application is the national phase of international application PTC/GB96/02468, filed Oct. 9, 1996. 
    
    
     This invention relates to a soil levelling device to be used with an impact roller. 
     BACKGROUND TO THE INVENTION 
     The term “impact roller”, as used initially in U.S. Pat. No. 2,909,106 refers to a soil compaction machine including a compactor mass of non-round shape which, when towed over a soil surface, produces a series of periodic blows on the soil surface. The compactor mass of an impact roller has a series of spaced apart, salient points on its periphery. Each such salient point is followed by compacting face with, in most cases, a re-entrant portion of the periphery between the salient point and the compacting face. As the impact roller is towed over the soil surface, for instance by means of a tractor, it rises up on each salient point and then falls forwardly and downwardly as it passes over that point, with the result that the following compacting face applies an impact blow to the soil surface. The coupling between the tractor and the compactor mass is resilient in nature to allow for the necessary forward and downward falling motion undergone by the mass as it passes over each salient point. In practice, as the compactor mass is moved over the soil surface, it produces a series of indentations in the soil surface which are spaced apart in the direction of movement of mass. The longitudinal spacing of the indentations is the same as the peripheral spacing of the compacting faces of the compactor mass. After one or several passes of the impact roller it is necessary to smooth the soil surface. This is typically done with the aid of a motor grader or, in some instances, using the blade of a bulldozer. In either case, the levelling operation requires a separate and expensive piece of equipment. Added to this the efficiency of the compaction operation is considerably reduced by the necessity for the use of levelling equipment after compaction has taken place. It has been proposed in WO 94/26985 to provide, in the case of an impact roller with two side by side compactor masses, a levelling blade arrangement which trails the compactor masses to apply a levelling action to the soil after passage of the compactor masses. With this proposal, it is possible to perform the levelling operation simultaneously with the compaction operation. It is an object of the present invention to provide a modified form of levelling device. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a soil levelling device for an impact roller, the levelling device comprising: 
     coupling means for coupling the levelling device to the impact roller so as to trail the impact roller in use; 
     a support frame; 
     at least one compactor mass; 
     for each compactor mass of the impact roller, a ground-engaging levelling blade fast with the support frame, the levelling blade being arranged to cut soil which has been traversed by the compactor mass and thereby to perform a soil levelling action; and 
     for each levelling blade, a ground-engaging shoe connected to the support frame for pivotal movement relative to the support frame about an axis transverse to the direction of movement of the impact roller, the shoe serving to control the depth of cut achieved by the levelling blade. 
     Means are preferably provided which are operable to vary the elevation of the, or each, levelling blade relative to the support frame. 
     Typically, the device of the invention will be used with an impact compactor having two compactor masses spaced transversely apart from one another, the support frame carrying two transversely spaced apart levelling blades and two transversely spaced apart, ground-engaging shoes, one levelling blade and one shoe being provided for each compactor mass. The support frame will then include a transverse beam mounted for pivotal movement about a fore-and-aft axis, the levelling blades and shoes being supported in spaced apart relationship at opposite ends of the transverse beam. 
     The device may also comprise lifting and lowering means operable to raise and lower the support frame relative to the soil surface traversed in use by the levelling device. The lifting and lowering means may, for instance, comprise a double-acting hydraulic cylinder acting between the coupling means and a bracket to which the transverse beam is pivoted, the pressurisation of the hydraulic cylinder determining the force with which the levelling blades are biased into engagement with the soil surface. In one embodiment of the invention, there may be an hydraulic accumulator connected to the cylinder, the hydraulic accumulator serving to damp reaction forces on the levelling blades. In another embodiment, the cylinder may act via a pressurised air bag on the bracket to which the transverse beam is pivoted, the air bag serving to damp reaction forces on the levelling blades. 
     In the preferred embodiments, each around-engaging shoe has fore and aft portions which respectively lead and trail the associated levelling blade. In one version of the invention, the fore and aft portions of each shoe are in the form of skid, while in another version of the invention, the fore and aft portions of each shoe are in the form of rollers or groups of rollers. According to another aspect of the present invention there is provided a method of compacting and levelling a soil surface, the method comprising the steps of coupling a levelling device according to any one of the preceding claims to an impact roller and causing the impact roller to traverse the soil surface, with the levelling device trailing behind the impact roller, so that the impact roller applies periodic compacting blows to the soil surface and the levelling device then applies a levelling action to the soil surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 shows a side view of a levelling device according to the invention coupled to a dual mass impact roller: 
     FIG. 2 shows an isometric view of the levelling device; and 
     FIG. 3 shows an isometric view of another embodiment of the invention. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     FIG. 1 illustrates a levelling device  10 , according to one embodiment of the invention, coupled to a dual mass impact roller  12 . The impact roller  12  is of conventional design and those skilled in the art of impact compaction will readily understand the operation thereof. For present purposes it suffices to say that the impact roller includes a pair of side-by-side compactor masses  14 , only one of which is visible in the FIG. Each compactor mass has an out-of-round shape with a series of peripherally spaced salient points  16 , each followed, for a direction of rotation  17 , by a re-entrant portion  18  and a compacting face  20 . The compactor masses  14  are spaced apart from one another and are mounted on a common axle  21  so as to rotate substantially in unison with one another. The axle is supported by a wheeled carriage  22 . 
     The impact roller is coupled in use to a tractive vehicle such as a tractor (not illustrated). During towing, each compactor mass successively rises up on a salient point and then falls forwardly and downwardly for the following compacting face  20  to apply an impact blow to the soil surface, thereby compacting it. Thus it will be appreciated that the potential energy of each mass when it is raised up on a salient point is delivered to the soil surface at each impact blow. 
     A coupling bracket  24  of the device  10  is bolted to the carriage  22  through bolt holes  26  (FIG.  2 ). One end of a double-acting hydraulic cylinder  28  is pivoted to the bracket  24  at an axis  30 . The other end of the cylinder  28  is pivoted to a fulcrum bracket  32  at an axis  34 . A transverse shaft  35  carried by the fulcrum bracket  32  is secured rotatably to the rear end of the carriage  22  as illustrated. 
     A transverse beam  36  extends through the fulcrum bracket  32  and is pivoted to the bracket  32  about a fore-and-aft axis  38 . The overall length of the beam  36  is slightly greater than the spacing of the outer surfaces of the compactor masses  14 . 
     The beam  36  carries brackets  40  towards either end as illustrated. Each bracket  40  supports a vertical adjustment mechanism  42  which is operated by a handwheel  44 . The handwheel is used to rotate a threaded shaft  46  coupled via a bracket  48  at its lower end to a levelling blade assembly  50 . Each levelling blade assembly includes an inclined, transverse levelling blade  52  with a cutting edge  54 . It will be appreciated that the levelling blades are carried rigidly by the beam  36  and that rotation of the handwheels  44  serves to raise and lower the cutting edges of the blades relative to the beam. 
     Freely pivoted to the ends of the beam  36 , at aligned pivot axes  56 , are shoes  58 . Each shoe has a front skid  60  and a rear skid  62  joined to one another by side plates  64 . Each skid  60 ,  62  has an upwardly curved leading end as illustrated. The levelling blade assemblies  50  are located in the gap between the front and rear skids and the cutting edges  54  project donwardly below the lower extremities of the skids. 
     The centre to centre spacing of the levelling blades and skids matches the centre to centre spacing of the compactor masses  14  and the arrangement of the device  12  is such that the levelling blades track behind the compactor masses. During forward movement of the impact roller the skids  60 ,  62  contact and slide over the soil surface. They are able to rock freely about the pivot axis  56  to take account of irregularities in the soil surface. High points which are left in the soil surface between the indentations which are created by the action of the compactor masses are trimmed by the blades and the loose soil is then evenly distributed by the action of the blades and of the skids  62  so that a generally smooth soil surface is obtained after each pass by the impact roller. 
     The overall length of each shoe is typically such that, as it traverses an indentation in the soil created by the associated compactor mass, it will span across the indentation, thereby keeping the levelling blades  52  slightly elevated relative to the bottom of the indentation and assisting in the spreading of the loose soil cut from the preceding high point. The necessary downward force on the levelling blades to enable them to perform the desired cutting action is generated by appropriate pressurisation of the cylinder  28  to pivot the main assembly downwardly about the axis of the shaft  35 . 
     It will be appreciated that, for a given setting of the handwheels  44 , the levelling blades will project a given distance below the skids  60 ,  62 . Since the skids  60 ,  62  are in contact with the soil surface, this distance determines the depth of cut achieved by the levelling blades. The depth of cut can of course be varied by appropriate rotation of the handwheels. 
     The beam  36  is able to pivot freely about the fore-and-aft axis  38  to take account of localised variations in the soil surface between one side and the other. The levelling blades  52  will generally have a transverse width which is slightly greater than the widths of the compactor masses, so as to perform a trimming operation both across the full width of the soil surface traversed by the compactor masses and for a short distance to either side thereof. The blades therefore apply a levelling action across the width of the indentations left by the compactor masses and for a short distance to each side thereof. The skids  60 ,  62  will have a width less than that of the blades so as to slide within the indentations left by the compactor masses. 
     Pressurised hydraulic fluid is supplied to the cylinder  28  from an hydraulic pump driven off the tractor or directly from the hydraulic system of the tractor. That working chamber of the cylinder  28  which is used to pressurise the cylinder to apply a downward bias to the levelling blades during levelling can be connected to an hydraulic accumulator (not illustrated) which acts as a damper to cushion the device  10  from shock loads which may arise if the levelling blades strike a hard obstacle such as a rock. For a given extension of the cylinder  28 , the accumulator pressure determines the downward force on the levelling blade. By varying the accumulator pressure, this force can be varied as required. 
     At the end of a levelling operation or when levelling action is not required the cylinder  28  can be retracted to lift the shoes and levelling blades clear of the soil surface. 
     In FIG. 1 it will be seen that the cutting edges  54  of the levelling blades  52  are off-set slightly to the rear relative to the pivot axis  56 . 
     It has been found that this off-set, in the context of the illustrated geometry of the levelling device, provides the device with an advantageous self-adjustment feature. When the shoe  58  is inclined donwardly, i.e. when the skid  60  is lower than the skid  62 , the blade projects further beneath the skids to perform a deeper cutting action than when the shoe is inclined upwardly, i.e. the skid  60  is higher than the skid  62 . With this feature, a substantial amount of soil can be cut by the blade, at appropriate locations, and transferred into the indentations left by the associated compactor mass. This facilitates the filling of each indentation with a sufficient quantity of soil for the formation of a smoothly compacted site. This feature of the illustrated design arises because the levelling blades are connected rigidly to the beam  36  while the shoes  58  are pivotally connected. 
     It will be appreciated that the illustrated device performs a soil levelling action immediately after passage by the compactor masses of the impact roller and can eliminate or reduce the requirement for a subsequent levelling action by a separate grader or other levelling machine. An important advantage is the provision of the shoes  58  which in general determine the depth of cut achieved by the levelling blades and which, with the illustrated geometry, allow for automatic variation of the cutting depth as they traverse indentations in the soil surface. 
     It will also be noted that the device is not an integral part of the impact roller itself, and can be attached or detached as required. 
     FIG. 3 illustrates a second embodiment of the invention. In this FIG. components corresponding to those seen in FIGS. 1 and 2 are indicated with the same reference numerals. One important difference between the embodiment of FIGS. 1 and 2 and that of FIG. 3 is the use, in FIG. 3, of shoes  58  which include fore and aft rollers,  70  and  72  respectively, instead of skids  60  and  62 . The rollers  70  and  72  are freely rotatable on shafts  74  and  76  supported by the side plates  64 . 
     In practice, the rollers  70  and  72  roll over the ground surface rather than sliding over that surface as is the case with the skids  60  and  62 . It is believed that a rolling rather than a sliding action will be preferable in situations where the ground surface is composed of low friction material such as coal or shale fragments. Another advantage of the illustrated rollers as opposed to skids is the fact that the rollers, being of quite small radius and each having only a small portion of its cylindrical surface in contact with the ground at any one time, will be able to follow the ground contour created by the action of the compactor masses more accurately, and hence will be able to control the depth of cut achieved by the blades  52  with greater precision. 
     In FIG. 3 the rollers are illustrated as having smooth outer surfaces. In practice, to improve the purchase of the rollers on the ground and to reduce the chances of the rollers slipping over the ground surface as opposed to rolling over that surface, the roller surfaces may be roughened and may, for instance, include studs or other ground engaging projections. 
     It should also be noted that instead of each shoe having a single fore and a single aft roller, there may be multiple rollers grouped together fore and aft of the levelling blades. 
     Another important difference between the embodiment of FIGS. 1 and 2 and that of FIG. 3 is in the nature of the suspension of the soil levelling device. In FIG. 3 the double-acting hydraulic cylinder  28  is as before, pivoted to a bracket  24  which is bolted to the carriage of the impact roller. Also as in FIGS. 1 and 2, the fulcrum bracket  32  is pivotally connected to the carriage by a pivot shaft  35 . In this case the cylinder acts on a lever  78 . The lower end of the lever  78  is pivoted to the fulcrum bracket  32  at a pivot shaft  80  and its upper end acts on an air bag  82 . Force is transmitted through the air bag  82  to the inclined surface  84  of a bracket  86  on the fulcrum bracket  32 . 
     As in the first embodiment, the downward load with which the levelling blades are urged into engagement with the ground can be varied by varying the pressurisation of the cylinder  28 . However, in this case, a damping effect to protect the levelling device from shock loads as a result of impacts with rocks and the like is provided by the air bag  82 , the inflation pressure of which determines the magnitude of the damping effect. It is believed that in some cases at least the use of an air bag is preferable to the use of an hydraulic accumulator connected to the cylinder  28 , since faster damping and restoration can be expected. 
     In FIG. 3, as in the first embodiment and for the same reasons mentioned above, the cutting edges  54  of the levelling blades  52  are off-set slightly to the rear of the pivot axis  56 .