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RELATED APPLICATIONS 
     This application is based upon provisional patent application Ser. No. 60/056,953, filed Aug. 26, 1997. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to road construction and maintenance apparatus, and more specifically relates to a system for working or generally cutting into the surface of a road, that is, to produce cavities or openings in the pavement surface for various purposes, among them, the installation of reflectors, the formation of rumble strips in the road surface, the boring of holes in the road surface, the cutting of a striping, the milling of potholes or generally to otherwise physically affect the road surface. 
     BACKGROUND OF INVENTION 
     There are many operations that are needed to be performed through working or in some way cutting into or affecting the surface of a road. For example, light reflective lane and border markers have come into ever increasing use on modem roads and highways. These well-known devices are installed in the pavement at spaced intervals extending in the direction of vehicular travel, so that a motorist traveling under darkened or inclement weather conditions may readily perceive the thereby defined lanes and/or borders of the roadway. 
     An example of the type of reflective device which is commonly used for the above purposes may be found in U.S. Pat. No. 4,174,184. Such device includes a pair of parallel elongated, laterally spaced apart keel members and an intervening portion having an arcuate part-cylindrical convex bottom portion, and an upper portion which receives a reflector assembly. The 4,174,184 patent also discloses a typical type of apparatus which can be used to form cavities in the road surface for receiving markers of the type discussed. Such apparatus includes a plurality of circular cutting or milling blades mounted on a common shaft. The outer blades are of an enlarged diameter as compared to the inner blades so that a cut can be formed in the road for matching the bottom shape of the marker. The shaft is in turn mounted on a wheeled cart that is towed to the location of each cut, where the cart is positioned so that the resulting cavity is at the desired locale for the emplaced marker. The assembly of rotatable circular blades (powered by an internal combustion engine, or hydraulic motor or the like) is placed in initial tangential contract with the road surface, and as it rotates controllably descends to the desired depth of cut. Because of this descending action, the assembly is sometimes referred to as a “plunge saw”, a term which at times will be used in the present specification. 
     Particularly in view of increased interest and awareness in road safety measures, the need for installing large numbers of the foregoing road reflectors has risen greatly. This is not to even mention the need to reinstall new reflective markers to replace or augment those which have become damaged as a result of normal weathering and wear and tear, particularly where extensive snow plowing of the road surface is a factor. While towed carts and the like are quite suitable for providing small numbers of installations, they do not lend themselves to large scale activities. The use of such rudimentary apparatus in turn leads to excessive installation costs for the many road building and installation agencies which seek to exploit the many safety advantages of the in-road installed type of light reflectors. 
     In several instances apparatus have been disclosed which endeavor to alleviate the disadvantages of simple towed and similar devices by providing automated plunge saws and the like which are mounted to a truck or similar vehicle. A very simple arrangement of this type is shown in U.S. Pat. No. 4,797,025, where a self-propelled cart carries a series of rotating blades to cut desired pavement slots. The blade drive shaft is powered by an hydraulic motor, and manually adjustable means enable the operator to set the depth of cut. 
     In U.S. Pat. No. 4,463,989 a portable road cutting machine is disclosed which is mounted on the forward end of a conventional truck body. The apparatus incorporates many hydraulic components, such as a large hydraulic reservoir, hydraulic lines and electronic hydraulic valves. 
     In U.S. Pat. No. 5,421,669, a further machine is disclosed for producing cavities in a roadway surface for installation of markers. The machine is mounted on a support base forming part of a powered vehicle that can be driven on the roadway surface where the road markers are to be installed. As in the 4,463,989 patent, heavy reliance is placed on numerous hydraulic components. Malfunctioning of such components can occur all too easily, e.g. a valve may remain open or closed, which can cause serious damage to the equipment or even the operator. Furthermore, in both of these truck associated systems the apparatus is so intimately connected with the vehicular carrier that dismantling of the system is a very complex and time-consuming task. 
     As examples of other functions that work or in some way affect the surface of a road, there is often formed in road surfaces, a series of grooves, commonly referred to as rumble strips, and which are formed by the use of an specially constructed apparatus, one of which is shown and described in U.S. Pat. No. 5,094,565 where a cutting tool is used having a plurality of cutting heads that can be used to form the rumble strip. As can be seen in that patent, a particular machine is dedicated to the formation of the rumble grooves and which forms a plurality of grooves simultaneously by milling the groves into the road surface. 
     As a further example of a road working function and apparatus, various boring machines are currently used to work the surface of a road and may be used to simply bore holes of a desired size to install different styles of reflectors and the like or can be used for the preparation of potholes so that the potholes are bored out to receive and hold the fresh asphalt in the alleviation of the pothole. 
     SUMMARY OF INVENTION 
     Now in accordance with the present invention, a system is provided for working the surface of a road to carry out variety of the aforementioned functions to that road, including the installation of reflectors, the formation of rumble strips, the boring of holes, cutting of line striping, pot hole milling by or for a variety of other functions that cut or work the road surface where the working apparatus requires some vertical adjustment to determine the desired depth of penetration. The system is defined in combination with a vehicle having a motor powered vertically movable rear lift gate which, in use, defines a vertically displaceable substantially horizontal platform. The particular rotating road working apparatus is secured to the upward facing surface of the lift gate with the apparatus itself being mounted on a rotatable drive shaft extending laterally of the gate. In one of the various embodiments, a series of cutting blades can be functionally connected to the rotatable drive shaft, and the cutting blades at least partially projecting below the bottom surface of the lift gate, whereby with the gate in a lowered position, the saw blades can engage the surface of the road on which the vehicle resides. In an alternative embodiment, the rotatable drive shaft may be connected to a differential coupling so that the horizontal rotating shaft can be converted to a vertical rotating shaft and that apparatus used to bore holes in the surface of the road or to mill the asphalt in the excavation of potholes. In any instance, a motor means is secured to the upper surface of the gate, and is connected to power the drive shaft; and means are provided to selectively adjust the vertical position of the lift gate with respect to the surface of said road, to thereby control the depth of cut and thus the degree of excavation produced by the particular road working apparatus. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention is diagrammatically illustrated, by way of example, in the drawings appended hereto, in which: 
     FIG. 1 is a schematic rear view of a system in accordance with the present invention, for producing cavities in a road surface into which reflective road markers are to be received; 
     FIG. 2 is a top plan view of the system of FIG. 1; 
     FIG. 3 is a left end view of the system of FIG. 1; 
     FIG. 4 is a right end view of the system of FIG. 1; 
     FIG. 5 is a perspective, partially broken-away view showing details of the vertical support rails and elevatable lift gate. The gate is shown without the mounted elements present; 
     FIG. 6 is a partially broken away view of the rail slider assembly that lifts the tail gate; 
     FIG. 7 is a partially broken away view of the left side slider assembly with safety switch; 
     FIG. 8 is a schematic left end view of the system showing the embodiment that produces rumble strips in the road surface; 
     FIG. 9 is a schematic rear view of the embodiment of FIG. 8; 
     FIG. 10 is a schematic rear view of a further embodiment of the subject intention that is employed to bore holes in the road or excavate potholes; and 
     FIG. 11 is a schematic rear view of the embodiment of FIG.  10 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1, which may be viewed simultaneously with FIGS. 2,  3 ,  4  and  5  schematically depicts a system  10  in accordance with the present invention for producing cavities in a road surface into which reflective road markers are to be received. System  10  is a combination which includes a vehicle  12  such as a truck, a portion of which is shown at  14  (FIGS.  3  and  4 ), which vehicle is provided with a lift gate  16 . The lift gate  16  is per se a well-known device for use with trucks and other vehicles to aid in loading and unloading. In use, such a conventional lift gate is placed (if not already so oriented) in a horizontal plane to define a platform for receiving loads. The lift gate is movable vertically between desired positions of elevation so that loads may be moved between the truck bed and a loading platform or other surface. This vertical movement is accomplished by electric or hydraulic motors which are actuated by an operator. Various types of lift systems are known for lift gates. A preferred arrangement for the present invention is one based on a rail lift. In this arrangement the platform is supported at the platform&#39;s edge closest to the vehicle by a pair of elevator members which are vertically movable in opposing vertical rails. Support members at or toward the platform&#39;s edge furthest away from the vehicle are attached to a further pair of elevator members which are vertically movable in the said rails. In this manner the platform is raised from each of the platform&#39;s four corners, thereby providing a more uniform lift. 
     In the present invention, a pair of vertical rails  18 ,  20  are secured to the rear of vehicle  12  by being welded or otherwise secured by brackets  22  to upright members  24 ,  26  at the rear of the vehicle  12 . As best seen in FIG. 5, a pair of movable supports  34 ,  36  are received within vertical rails  18 ,  20  for vertical movement. The lift gate  16  is attached at its inner end  32  to movable supports  34 ,  36  movable within the vertical rails  18 ,  20  by the drive chain  31 . Support bars  44  and  46  extend between the movable supports  34 ,  36  and lift gate  16 ; and safety chains  50  are also provided between the same elements to provide an added safety measure. Accordingly the lift gate  16  is movable vertically within the vertical rails  18 ,  20 . Lift gates and chain drive systems for same which are useable in the present invention are available from several sources, such as Thieman Life Gate Company of Celina, Ohio. The motive means for lifting the movable rails and lift gate is generally conventional, and may comprise an electric motor which is powered by the vehicle or other battery, and a chain and gear drive. Noteworthy for the present invention is that such power is only required for elevating lift gate  16 ; the gate descends gravitationally under its own weight and the weight of such load as may be present on the lift gate  16 , which can be regulated by a hydraulic flow controller  33  that is installed in line inside the access panel  35 , the cover  37  of which is removed in FIG. 5 to show the internal components. 
     In accordance with the present invention, essentially all major active elements of the system  10 , including the powering means, are directly mounted on platform  38  of lift gate  16 , so that such major elements may move vertically therewith to effect upon descent the desired action to the surface of the road. More specifically a motor means such as a compact gasoline or diesel driven engine  40  is secured to platform  38  of lift gate  16 . A fuel tank  42  is mounted to the upright member  24  together with fuel lines  101  which connect the fuel tank ( 42  to engine  40 . The drive shaft  52  of engine  40  transfers power through pulley  41  and drive belts  54  to the power shaft  56 , which as best seen in FIG. 1 extends to one side of vehicle  12  and lift gate  16 . In accordance with the first embodiment, the power shaft  56  carries at its projecting end a generally conventional milling saw assembly  58 . Such milling saw assembly  58  includes a series of blades mounted for rotation on the shaft  56 , i.e. an outer pair of blades  60  and  62  of an enlarged diameter, and a series of inner blades  64  of a reduced diameter. The various blades, and the milling saw assembly  58  are per se all conventional, and have been used in the prior art to excavate the cavities which are of interest to the present embodiment. In the system  10  depicted, a single milling saw assembly  58  is shown to reside at one side of the vehicle  12 , although in practice a further assembly can be mounted at the other lateral side of vehicle  12 , and driven by the same power shaft  56 . See FIG. 2, where power shaft  56  (journaled in block bearings  57 ) is connected to a splined adjustable drive shaft  105  (power shaft  56  is shown broken away in FIG. 2) which may be connected to a splined yoke shaft  105 , thence through universal joint  61  and shaft  63  to a removable shaft hold down extension  65 , to support extended shaft and hold down block bearing  57 , to enable different milling lengths for the total shaft length. This enables the user to excavate pairs of cavities simultaneously for selected spacings between the members of the pair, e.g. for 10 or 12 foot wide, etc. traffic lanes. It will be seen in FIG. 1 that two slip couplings  66 ,  68  are inserted in the power shaft drive train, which enables different driving arrangements as required for a given project. A drive shaft lifting adjuster  70  is also provided to enable adjustment for possible differences in roadway distance from the shaft on alternate sides of the vehicle. Side and top blade guards  72  and  74  surround exposed portions of the blades to further protect operators of the present system. 
     In use, the engine  40  is operated via throttle  43  to effect turning of the milling saw assembly  58 . Power is preferably transmitted through the one or more couplings  66 ,  68 , and a clutch may be incorporated in the power train to increase control and safety. Initially the lift gate  16  is in an elevated position whereby the milling saw assembly  58  is out of contact with the road surface. The raised position is of course also appropriate for transport to the work site, and when moving between areas at the site where installation of reflectors is to be carried out. A removable transport locking pin  76  is provided as a safety measure to assure that the raised lift gate is not accidentally lowered prematurely or during transport. A pair of depth adjusters  78  and  80  are mounted through the platform  38 , with the lowermost feet of the depth adjusters  78 , 80  being manually displaceable by the system operator to desired vertical positions. This provides a limiting means for downward descent of lift gate  16  with the milling saw assembly  58 , thereby to control the depth of the cut in the road surface. 
     During the descent of lift gate  16 , the movable lift gate  16  slides downwardly under gravitational force. The rate of descent is controlled by a controlled hydraulic bleed from the piston and cylinder arrangement  59 , the hydraulic fluid displaced from the cylinder during the descent being bled through a control valve at hydraulic flow controller  33 , the setting of which thus regulates the rate of platform descent and thereby the rate at which the rotating cutting blades descend into the roadway surface. During cutting, a stream of cooling water is fed to the cutting blades via a nozzle  82  in order to prevent damage to the expensive (usually diamond studded) cutting surfaces. The water is fed gravitationally from a tank (not shown) mounted in the truck bed. Water flow may be monitored by the water flow meter  86 . Safety mud flaps are also provided at  88  and  102  to prevent throwing off of materials from the rotating blades as the cuts are made. In the absence of these flaps, mud and road materials can be ejected toward operators or other workers resulting in injury or worse. Subsequent to the cut being effected, the movable platform  38  is raised with the lift gate  16 . Upward movement of the lift gate  16  is limited by a limit switch  90  which is actuated by contact with the end face of support bar  44  with the ascending movable support  34 . 
     Since the production of the cuts in the roadway surface is an operation often carried out at night so as to minimize interference with traffic, a series of lights may be provided as at  96 , as well as strobe lights  98 . Reflectors as at  100  are also provided at the rear of the system as an added safety measure. 
     Control of the entire operation of the system  10  may be carried out by a control box  103 , which is connected to the various control switches through a flexible cable  104 . 
     As can readily be seen, the aforementioned embodiment was describes with the use of a milling saw assembly, however, as can also be seen, the milling saw assembly can be replaced with a variety of other rotating apparati, including a narrow rotating saw to cut a narrow strip into the surface of the pavement for use in the installation of a 3M adhesive yellow tape that interfits with the depression cut by the saw. In such case, the depression or taper can be cut into the surface of the road in a width of about one eighth of an inch for the installation of such striping and therefore the milling saw can readily be replaced with the appropriate width saw without departing from the spirit of the present invention. Additionally, other sizes of milling saws can be used and in such case, the milling saws can be readily used to excavate pot holes easily and without the need to provide a separate movable apparatus to move into position, carry out the milling and them be manually movable from the location. 
     Turning now to FIGS. 8 and 9, there is shown an alternate embodiment of the present invention and where the system  10  is used to mill rumble strips into the surface of the road. As shown in this Figure, the power shaft  56  operates a multi-head cutting tool  108  that can be used to mill a plurality of grooves in the surface of the road simultaneously in order to create a rumble strip. In this embodiment, the power shaft  56  can rotate two secondary pulleys  110  by means such as belts  112  which, in turn may operate two cutters each,  114  that, in turn operate additional cutters  114  through a series of belts  116 . In this manner, the power shaft  56  rotating in a horizontal plane can operate the plurality of cutters  114  to mill the grooves in the road to produce rumble strips. Again, in accordance with the spirit of the present invention, the use of the lift gate  16  is utilized to move the multi-head cutting tool  108  vertically to determine the depth of the various grooves and that operation to establish that depth is readily controlled by the operator by means of the control box  103 . 
     Finally. Turning to FIGS. 10 and 11, there is shown a still further embodiment of the present intention and where the system  10  can be used to bore holes in the road for various purposes, such as the securing a variety of structures to the road, such as, but not limited to, different styles of reflectors. In this embodiment, a differential  118  is used to convert the horizontal rotation of the power shaft  56  to a vertical rotation so that the apparatus can bore holes generally vertically into the road surface. A coupling  120  of conventional design allows the attachment of a boring bit  122  of differing sizes to account for the variety of operations on the road that involve the boring process and therefore any number of differing sizes of boring bits can be used. 
     While the present invention has been set forth in terms of specific embodiments thereof, it will be understood in view of the instant disclosure, that numerous variations upon the invention are now enabled to those skilled in the art, which variations yet reside within the scope of the present teaching. Accordingly the invention is to be broadly construed and limited only by the scope and spirit of the claims now appended hereto.

Summary:
An assembly is provided for excavating cavities in a road surface for a variety of purposes, among them, the formation of rumble strips, the installation of light reflective road markers, the milling of potholes, boring of holes for various purposes and the like. The system is used in combination with a vehicle having a motor powered vertically movable rear lift gate which in use defines a vertically displaceable substantially horizontal platform. A cutting apparatus is secured to the upward facing surface of the lift gate with the actual cutting portion being mounted on a rotatable drive shaft extending laterally of the gate, such that the cutting portion projects at least partially below the bottom surface of the lift gate, whereby with the gate in a lowered position, the cutting portion can engage the surface of the road on which the vehicle resides. A motor is secured to the upper surface of the gate powers the drive shaft. The vertical position of the lift gate is adjustible with respect to the surface of said road, to control the depth of cut and thus the degree of excavation produced by the cutting apparatus.